Cooking can be an art. Feed and let them be. Some can camouflage e. A tropical horde of counterfeit predator eyes. These cells have very long axons at the end of which are motor end plates where the nerve cell can stimulate the effecter organ.
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The main problem with this most productive avenue of food gathering is protection. Shells and poisons are the major types of defenses, although innovative detoxification metabolism and jaws of various kinds breach the defenses in part. This is an escalating battle in which the defenses, as well as the weapons to penetrate them are continually improving.
Nudibranchs, shell-less marine snails, incorporate the defensive stinging cells of prey cnidarians into their own skin. Poisonous plants are eaten by specialized insects that avoid or detoxify the poison. In fresh water, for reasons not known, the arms race has not proceeded as far as in the sea. Cooperation of individuals enables social animals to obtain food in novel ways. Uncannily like humans, some ants farm and herd other organisms for food.
For example, some cultivate a fungus on leaves they cannot directly digest, while others herd aphids from which they milk nectar actually the phloem sap of plants. Some ants even raid the nests of other species and make slaves of them. Another form of cooperation is the mutualism between species that trade advantage for advantage.
Some fishes feed on parasites on the surfaces of other fishes, which benefits all but the parasites. In many animals, including termites and ruminants, microorganisms thrive in the gut and digest cellulose for them. Coherent movement results only when the muscles receive a sensible pattern of activating signals for example, antagonists must not be activated to contract simultaneously. Animals use specialized cells called neurons to coordinate their muscular activity; nerves are bundles of neurons or parts thereof.
Neurons communicate between cells by chemical messengers, but within a single cell often extremely long they can send high-speed signals through a wave of ionic polarization analogous to an electric current along their membranes, a property inherent in all cells but developed for speed in nerve cells by special modifications.
A system of communication requires three parts: In animals, sensory nerves and organs such as eyes collect the information; associative nerves usually concentrated into a brain integrate , evaluate, and decide its relevance; and effector or motor nerves convey decisions to the muscles or elsewhere.
Although all three parts of the nervous system have kept pace with increases in the size and complexity of animals, the simplest systems found among animals those of parazoans and coelenterates are nevertheless capable of intricate feats of coordination.
All ends of a coelenterate bipolar neuron can both receive and transmit an impulse, whereas the unipolar neurons of more derived animals receive only at one end dendrite and transmit at the other axon.
A neuron can have multiple dendrites and axons. The earliest animals were probably radial in design, so that bipolar neurons arranged in a netlike pattern made sense.
In such a design, a stimulus impinging at any point on the body can travel everywhere to alert a simple array of myofilaments to contract simultaneously. In the case of directed locomotion and relevant sensory input received at the head end of a bilateral animal, unidirectional transmission of nerve impulses to muscles becomes the only way to communicate effectively. The location of the brain in the head also reflects efficiency and the speed of receipt of information, because this position minimizes the distance between sensory and associative neurons as well as concentrates these two functions in a small, protected part of the body.
In most animals nerve cells cannot be replaced if lost, although axons can be. Nerve cells tend to be concentrated centrally in ganglia or nerve cords, with long axons extending peripherally. Although certain animals may lose tails or limbs to predators or in accidents and then regenerate them, loss or damage to the central nervous system means death or paralysis.
The nervous system uses the transmission properties of neurons to communicate. To pass to the next cell at a synapse, where an axon meets a dendrite, a chemical transmitter is required. Although chemical transmission is considerably slower than the ionic wave, it is more flexible. For example, learning involves in part increasing the sensitivity of a particular nerve pathway to a stimulus.
The sensitivity of a synapse can be altered by increasing the amount of transmitter released from the axon per impulse received, increasing the number of receptors in the dendrite, or changing the sensitivity of the receptors.
Bridging the synapse directly by the formation of membrane-bound gap junctions , which connect adjacent cells, enables an impulse to pass unimpeded to a connecting cell. The increase in speed of transmission provided by a gap junction, however, is offset by a loss in flexibility; gap junctions essentially create a single neuron from several. The same result can be achieved more effectively by lengthening the axons or dendrites, making some nerve cells metres in length.
Situations arise where gap junctions become desirable, however. Gap junctions are found in vertebrate cardiac and smooth muscles, both of which transmit impulses along their cells to others. This ability makes these muscles somewhat independent of nervous-system control.
A body can thus be kept partly functioning for some time without the activity of a brain. Nerve impulses travel faster along axons of greater diameter or along those with good insulation against ion leakage except at spaced nodes required for recharging.
Vertebrates use their unique myelinated axons to increase the transmission rate of nerve impulses, whereas invertebrates are limited to using axons of greater diameter. As a result, vertebrates can concentrate more small neurons into a body of a particular size, with the potential for greater complexity of behaviour. Memory is still a poorly understood aspect of the nervous system.
As in learning, both short- and long-term memories seem to involve alterations in the ease with which subsequent impulses travel a particular pathway after it has been used. Transfer of memory through direct ingestion of the brain has not been confirmed experimentally.
Although the underlying mechanisms are only dimly understood, it is known that there is a correlation between learning and memory capacity. The capacities for both increase with the number of associative neurons and the number of branches or interconnections formed.
Since learning is a process of associating incoming cues with appropriate motor or internal response, greater memory capacity of a brain gives a more rapid learning process. Memory of inappropriate responses to an incoming set of cues can be used without motor repeat. The degree to which the neurons of a brain develop interconnections is correlated with the complexity of its environs while growing.
Basic, repeated behaviours are inherited or learned by the development of fixed pathways by which an environmental signal reaches the motor nerves rapidly with little or no variation reflex arcs. Nonreflex behaviour requires a decision to be made in the brain, with the resulting pathway to the motor nerves becoming more fixed habitual as one particular decision seems always to be correct. Reflexes are faster than decisions, but their relative adaptiveness depends on context. Animals vary in the degree to which they use reflexes or make decisions, patterns that are strongly correlated to brain size.
Habitual actions are perhaps the most prevalent response, a compromise between the speed of a response and its appropriateness to context. Appropriate behaviour relies on receiving adequate information from the environment to alert an animal to the presence of food, mates, or danger. Although sensory nerves carry this information to the brain, they do not always directly perceive the external world.
Other modified cells intervene to convert light waves into vision, pressure waves in air or water into sound, chemicals into smell or taste, and simple contact into touch. Some animals have other senses, as for electric or magnetic fields.
In vision , for example, a photosensitive molecule changes shape and thereby sets off a chain of reactions that ultimately depolarize the dendrite of a sensory nerve. The associative neurons in the brain interpret the pattern of incoming impulses into a composite picture.
The accuracy of what is seen increases with brain size and the complexity of the visual gathering system, or eyes. Animal eyes range from being able to discern only the presence or absence of light to being able to see objects in vivid colour and great detail. Some animals see in ranges beyond unaided human vision. Pollinating insects in particular discern the colour of flowers differently than do humans; the ultraviolet reflection patterns of flowers do not always coincide with their coloured ones.
Bees and birds perceive polarized light and can orient themselves by it. Some animals perceive long wavelengths, which are associated with heat infrared , and can locate the presence of warm-blooded prey by such a mechanism. Chemoreceptors are usually little-modified sensory neurons, except for the taste receptors of vertebrates, which are frequently replaced cells in synaptic contact with permanent sensory neurons. Chemoreception is based on the recognition of molecules at receptor sites, lipid-protein complexes that are liberally scattered on the dendrites of a sensory neuron.
When the receptor recognizes one particular molecule by shape and sometimes chemical composition , it fires an impulse. The pattern of firings set off in the receptors of a certain molecule provides the information that the brain interprets as an odour or a taste. The details of how animals smell and taste are not as well understood as are the other senses. In many animals, chemoreceptors are not concentrated into obvious organs as they are in vertebrates, making even their location difficult to discern.
Sounds are waves of molecular disturbance that move through air, water, or solids, and their perception by animals simply uses sensitive mechanoreceptors. Loud sounds can also be felt by the general touch receptors of the body and thereby influence its sense of well-being. Sound receptors are sensitive hair cells or membranes that depolarize a sensory neuron when bent by the passage of a sound wave.
Direct deformation of the dendritic membrane or release of transmitters by the hair cells fire the sensory neurons. Aside from a few insects, only vertebrates have organs with which to hear.
Fishes and aquatic amphibians use a lateral-line system , and other vertebrates use ears; both organs use hair cells as phonoreceptors. Sound waves directly stimulate the hair cells of lateral-line systems, while sound waves only indirectly stimulate the hair cells of ears through an amplifying system of membranes and bones, which reaches a peak of complexity in mammals.
Sound is the preferred medium of communication between animals that hear. It can be used over longer distances than vision, and it can be used when vision is not possible. The signals decay more rapidly than do those of odours, and therefore the information can be more precise. Mechanoreceptors also respond to touch, pressure, stretching, and gravity. They are located all over the body and enable an animal to monitor its state at any moment. Much of this monitoring is subconscious but necessary for normal functioning.
Mechanoreceptors are often just sensory nerves, but other cells may be involved. Unlike other senses, that of touch is found in all animals, even sponges, where it reflects a general cellular trait of eukaryotes. Hormones are the chemical integrators of a multicellular existence, coordinating activities from daily maintenance to reproduction and development. The neurotransmitters released by axons are one class of chemical communicators that act on an adjacent cell, usually a muscle cell or another neuron.
Hormones are a mostly distinct class of chemical communicators secreted by nerves, ordinary tissue, or special glands; they act on cells far removed from the site of their release. They can be proteins, single polypeptides, amines, or steroids or other lipids. Hormones travel to their place of action via the circulatory system and then match their particular configuration with a specific receptor molecule attached to a cell membrane or, more usually, located within the cell.
The nervous system coordinates the more rapid activities of animal life, such as movement, while the hormones integrate everything else.
Only the larger, more complex animals, such as vertebrates and some arthropods, have special endocrine glands to produce hormones; other animals use nerve cells or tissues such as the gonads. Endocrine glands are another example of a partitioning of functions into separate organs, a system that increases efficiency but that requires a relatively large size to maintain. Greater specialization is also associated with greater difficulties in regenerating lost parts or preventing breakdowns in functions.
Although the list of hormones found in the mammalian body may seem large, the numbers are surprisingly low for the variety of functions they influence. Which of the multiple functions any one hormone regulates depends on the specificity of the receptors on or within cells. Because all hormones bathe all cells as a result of their transport by the circulatory system, it is more efficient to have a general messenger transported to a cell, where it elicits only one of many possible outcomes.
As in the nervous system, the specificity of response lies in the organ that responds and not with the messenger that merely commands action. Chemicals that allow communication among individuals are called pheromones. Sexual attractants are the most common, but there are many other kinds. In contrast to plants, the essential nutrients that animals require to sustain life and to reproduce come packaged with their source of energy—the flesh or organic remains of other organisms.
More complex animals tend to shorten and even eliminate many synthetic pathways, because most of the essential building blocks of their own complex molecules are present in their food. Reducing synthetic flexibility, however, inhibits a radical alteration in diet.
The digestive and synthetic chemistry of animals strongly reflects their diets; some of this design may be altered with diet, and some may not. No matter how many leafy vegetables humans consume, for example, the cellulose remains undigested because appropriate microorganisms are not present in the digestive tract and they cannot be obtained at will.
Consequently, essential nutrients are species-specific and tend to include only molecules adequately available in the usual diet. The structure of a digestive system reflects its typical diet. Its purpose is to process food only to the point at which it can be transported to other cells for use as either fuel or structural material. In the simplest animals, such as sponges or some coelenterates, digestion is entirely intracellular, and some of the products of digestion are transported to nondigestive cells.
As animals began to catch larger types of food, more of the digestive process had to be handled extracellularly. At the simplest level, seen in coelenterates or flatworms, large food items are held in an internal cavity the gut or even externally where certain cells release digestive enzymes.
The food is broken down only to the stage at which it can be ingested by cells, which finish the process intracellularly. In more complex animals extracellular digestion accounts for virtually all breakdown of food before the products are transported to nondigestive cells.
Chemical digestion, whether intracellular or extracellular, is a relatively slow way to decompose a large item. Thus, animals begin to break it apart mechanically before exposing it to digestive enzymes.
Teeth, the molluscan radula , and muscular gizzards are organs that speed up the digestive process by macerating food into finer particles. Very early in their evolution animals acquired a one-way gut gastrointestinal system , with the mouth typically armed with the macerating equipment and the terminal stretch sometimes specialized to retrieve excess water or other nutrients.
Often a single passage through the digestive system leaves a great deal of useful material unclaimed. Because food moves along at a characteristic rate, which is sometimes influenced by how much is coming in, not all can be fully digested. Some animals regularly eat their feces to retrieve nutrients that may have escaped during first passage. If not recycled by their owners, feces are consumed by a diverse set of organisms. A common specialization of the gut is the stomach or crop—a highly extensible part of the digestive tract that is used to hold a large amount of food and partially digest it before it enters the intestines, where most of the chemical breakdown and absorption of nutrients occurs.
Most animals eat intermittently; the less often they eat, the larger the relative stomach size. Internalizing as much food as possible when it is available prevents potential food from being taken by a stronger competitor or enables a feeder to retreat to safety while digesting its meal.
Ceca and second stomachs provide symbiotic microorganisms with a safe area within the gut to digest cellulose. Excess microorganisms mixed in with the partly digestible wastes contribute a steady protein-rich fare to the host in exchange for an optimal place to consume cellulose. Stomachs predominate as a gut specialization because they allow animals to keep food from competitors or other dangers, but a few animals have developed ingenious methods of digesting their food before ingesting it.
Humans are latecomers to this practice and have not yet carried it very far. Starfish exploit secondary radial symmetry and tube feet to open bivalved mollusks only enough to inject their stomachs, digest their meal within the protected shell, absorb the products, and leave the wastes behind.
Spiders immobilize prey by silk wrappings and venoms, inject digestive enzymes, and drink the brew. Some primitive animals, like placozoans and certain flatworms, simply hunch over their prey as they digest it externally, a practice that leaves them vulnerable to other predators.
Animals use surfaces in many ways but no more strikingly than in the gut. Nutrients enter the body proper through the surface membrane of the gut; the larger the animal, the larger this surface area must be. The simplest guts, found in animals from sponges to flatworms, simply branch like trees as the animal increases in size; the gut itself reaches all parts of the body to within the distance of a few cells and thus can serve for nutrient transport.
As muscle masses become more prominent, the gut is squeezed into a more compact form. The gut compensates for this lack of space by internalizing its foldings.
For example, the lining of the mammalian small intestine , the major site of digestion and absorption, is not only folded but each cell also has numerous outpocketings microvilli , which increase the surface area fold. Mammals and birds that primarily eat plants have longer intestines than those that favour meat.
Warm-blooded animals, which maintain constant internal temperatures, require a great deal more energy than cold-blooded ones and thus tend to concentrate more surface area into a gut.
Although they are not efficient energy users, it is to their advantage to obtain more usable energy even if efficiency is lost in the process. Animals live in an aquatic environment even on land. Each cell is in contact with the ocean or its aqueous equivalent, which carries food and oxygen to the cells of the animal and carries its metabolic wastes away.
Smaller animals simply use the fluid-filled coelom for transport. Increasing size, however, places too many cells beyond diffusion distance from either the coelom or the outside. A muscular pump attached to muscular vessels has arisen in larger animals to move the interstitial fluid surrounding the cells.
Most animals have open circulatory systems. Those few animals with closed circulatory systems have a continuous series of vessels to circulate fluid to the vicinity of all cells, whereas those with open systems have vessels only near the heart. Actually, no system is entirely closed or open. In open systems the interstitial fluid and the circulatory fluid are the same, but in closed systems the two fluids can differ considerably in composition.
Closed circulatory systems have several advantages that make them more appropriate than open systems for large, active animals: For example, cephalopods, alone among the mollusks, and nemerteans, the most active of acoelomates, have closed systems, as do all annelids and vertebrates. Decapod crustaceans, the largest living arthropods, have nearly closed systems.
The most fully open systems have a heart with a few vessels leading from it, while fully closed systems both leak fluid which is reclaimed by the open lymphatic system and have open sections.
For example, blood flow in the vertebrate liver is partly open. In closed systems, blood flow can be both higher and directed more often to tissues that require a greater perfusion of blood. If blood is confined within discrete vessels, most of which are muscular, contractions can vary the flow rate according to need by altering the amount of constriction.
Thus, the heart beats faster during exercise, when the muscles need more oxygen. Fear changes the distribution of blood flow to ready the muscles for possible imminent action. The more muscular arteries, which carry oxygenated blood to the tissues, can proliferate more finely in active tissues so that more cells are closer to the capillaries, where exchange takes place. Another advantage of a closed system is the ability to carry a high density of oxygen-bearing cells.
Such cells cannot flow smoothly through the sometimes tight interstitial spaces and thus are not much used by animals with open systems. A great deal more oxygen, however, can be carried if the oxygen carrier such as hemoglobin is packed into cells.
The viscosity of the blood is a function of how many discrete particles are contained within it, and size is of little influence. If all the hemoglobin in the blood of humans were released by dissolving the cell membranes, it would be a thick gel unable to flow.
Animals with open systems do aggregate their oxygen carriers into giant polypeptides, but single molecules have limits to their size. Myriapods and insects, highly active arthropods with open systems, circumvented this problem by evolving a tracheal system of respiration, as have some other groups: A few types of cells protect organisms from a potentially hostile outside environment. Internal cells thus can eliminate any unnecessary ancestral life-support components as they specialize for various functions.
Bananas and plantains originally grew wild in damp, warm forest areas. They have probably been used as food by humans since earliest times. Bananas and plantains are now cultivated extensively in many of the humid tropical areas. Some peoples such as the Buganda in Uganda and the Wachagga in the United Republic of Tanzania depend on plantains as their main food. A g portion of green bananas or plantains provides 32 g carbohydrate mainly as starch , 1.
Plantains also have a high water content. Their very low protein content explains why kwashiorkor commonly occurs in young children weaned on to a mainly plantain diet. Bananas usually contain about 20 mg vitamin C and mg vitamin A as beta-carotene equivalent per g. For this reason fresh fruits and vegetables are much less important in the diet for those whose staple food is banana than for those whose staple is a cereal or root. Bananas are, however, low in their content of calcium, iron and B vitamins.
As bananas supply only 80 kcal per g, about 2 kg must be eaten to provide 1 kcal. Plantains are usually picked while they are still green. The skin is peeled off and they are then either roasted and eaten, or, more commonly, cut up, boiled and eaten with meat, beans or other foods. Plantains are frequently sun-dried and made into a flour. The trees are widely grown in Indonesia, but sago as a food is particularly popular in certain Pacific islands.
Sago has low protein content. Sugar, as sold in shops, is almost percent sucrose and is essentially pure carbohydrate. In Africa, Asia and Latin America nearly all locally produced sugar comes from sugar cane, while in Europe and North America some comes from sugar beet. In areas where much sugar cane is grown, the consumption of sugar or sugar-cane juice chewed cane is often high. In other parts of the world the consumption of sugar tends to rise with economic advancement.
In the United States and the United Kingdom in about 18 percent of energy consumed came from sugar sucrose , mainly in sweetened foods. In contrast, in many African countries less than 5 percent of energy comes from sucrose.
Sugar is a good and often inexpensive source of energy and can be a valuable addition to bulky energy-deficient diets. Contrary to popular belief, customary consumption of sugar is not related to obesity, diabetes, hypertension or any other non-communicable disease. Frequent sugar consumption can be associated with dental caries when coupled with poor oral hygiene, but sucrose is no more cariogenic than other fermentable sugars. White sugar contains no vitamins, protein, fat or minerals.
Many people find that its sweet taste adds to the enjoyment of eating. The yields of energy per hectare of land are very high on productive sugar estates. From time immemorial honey has been extensively gathered in developing countries from wild hives. Now more and more hives are being kept, often in hollowed and suspended pieces of tree-trunk or in other more managed ways. The incentive to keep bees tends to be the high price of beeswax rather than just the honey. Honey has gained the false reputation of being of special nutritive value.
In fact it contains only sugar carbohydrate , water and minute traces of other nutrients. Although merely a source of energy, it has sensory value as a pleasant food for humans.
Beans, peas, lentils, groundnuts and their like belong to the botanical family of Leguminosae. Their edible seeds are called legumes or pulses. Agriculturally the plants of this group have the advantage of being able to obtain nitrogen from the air and also add some to the soil, whereas most other plants take nitrogen from the soil and do not replace it.
Legumes usually thrive best when they can get water early in their growth and then have a warm dry spell for ripening.
They are therefore often planted at the end of the rains to ripen early in the dry season. In Africa, Asia and Latin America the seeds are usually left on the plant to reach full maturity and are then harvested and dried.
Some may be picked earlier and eaten while partly green, as in Europe and North America. Some varieties are susceptible to attack by weevils; spending a small amount of money on insecticides to prevent this is definitely economically sound.
However, care must be taken to ensure that an excess of insecticide is not applied, that the insecticide is relatively safe and that the beans are well washed before cooking. The legumes are very important from a nutritional point of view because they are a widely available vegetable food containing good quantities of protein and B vitamins in addition to carbohydrate.
Some legumes, such as groundnuts and soybeans, are also rich in oil. They usually supplement very well the predominantly carbohydrate diet based on cereals. Most legumes contain more protein than meat, but the protein is of slightly lower quality because it has less methionine.
However, when pulses and cereals are eaten together at one meal they supply a protein mixture containing good quantities of all the amino acids, which improves the protein value of the diet. Legumes also contain some carotene provitamin A and ascorbic acid if eaten green. Similarly, dried legumes allowed to sprout before eating have good quantities of ascorbic acid. Some legumes contain antivitamins or toxins see Chapter Unless there is a very good reason for introducing a new crop such as soybeans, it is more sensible to encourage increased production and consumption of whatever legume is already grown and popular in any area.
The local people will have a taste for it, and agricultural conditions are usually suitable. It is also highly important to try to introduce beans and other pulses into the diet of children at an early age. Children are just as able as adults to digest beans easily. A wide variety of beans, peas, lentils, grams, etc.
All three regions have indigenous legume varieties but also grow varieties that originated on other continents. There are many kinds of beans. Haricot or kidney beans Phaseolus vulgaris were originally from the Americas but are now widely grown in Asia and Africa. Broad beans Vicia faba are more common in temperate areas.
Lima beans Phaseolus lunatus originated from Peru but are eaten all over the tropics and subtropics. Mung beans Phaseolus aureus , indigenous to the Indian subcontinent, are small seeds but very popular. Scarlet runner beans Phaseolus multiflorus are popular as a fresh vegetable in Europe and North America, but the large mature seeds are eaten dried in many countries. Lentils Lens esculenta and some similar legumes often known as grams are very important in the diets of people in many developing countries.
Lentils have been cultivated for food by humans for thousands of years. The plants are of small size, as are the seeds. Grams include the important pigeon pea Cajanus cajan , chickpea Cicer arietinum and green gram or mung bean Phaseolus aureus. In many South Asian countries various dhals made from these legumes form a significant part of the diet, providing important nutrients to supplement the staple food, which may be rice or wheat.
In many parts of Africa both cowpeas and pigeon peas are grown and consumed. The pigeon pea is perennial and relatively drought resistant. Lathyrus sativus, another drought-resistant legume, is grown widely in India, but consumption of large amounts can lead to the severe toxic condition called lathyrism see Chapter Winged bean Psophocarpus tetragonolobus is another important legume with a very high protein content 35 percent , but it is not yet widely grown.
Peas are commonly consumed as a green vegetable fresh, canned or frozen in Europe and North America and by more affluent people elsewhere. In developing countries the seeds are allowed to mature and are dried and consumed in the same manner as other legumes. These legumes excluding soybean all have a somewhat similar nutritive value, but the mature beans are eaten in a variety of ways and have different flavours and other culinary qualities.
Most legume seeds usually contain about 22 percent protein as opposed to 1 percent in cassava roots and 10 percent in maize and good quantities of thiamine, riboflavin and niacin; in addition they are richer in iron and calcium than most of the cereals.
The large number of other legume seeds of various shapes, colours and sizes on sale at food shops or marketplaces in almost any village or town in tropical countries is evidence of an appreciation of dietary variety and culinary finesse. Culture and local taste importantly determine how these foods are eaten.
However, the soybeans produced by these countries are mainly used commercially for oil and as animal feeds. Asia still produces much of the soybeans for direct human consumption. They are not widely grown in Africa or Latin America. Soybeans contain up to 40 percent protein, 18 percent fat and 20 percent carbohydrate. The protein is of a higher biological quality than that from other plant sources. Soybeans, used in a wide variety of ways, are very important in the diets of the Chinese and in those of some other Asian countries.
In China soybeans are made into a variety of tasty dishes which supplement the staple food of rice or other cereal. Soy products such as tofu soybean curd and tempeh a fermented product are important in Indonesian cuisine and popular elsewhere. Soybeans have not become a popular food in Africa or Latin America, where there is little local knowledge of the best methods of preparing them.
People lacking experience with soybeans find them difficult to prepare and cook. Where soybeans are grown they can be locally processed for use in the country as an enrichment of cereal flours, as an infant food or for institutional and school-feeding purposes. The oil can be exported and the protein-rich residue cake can be utilized in the country. The term "groundnut" is a misnomer since, although botanically a nut, the groundnut Arachis hypogaea is a true pulse, a member of the Leguminosae family.
It originated in Brazil but is now extensively grown in warm climates around the world. It is an unusual plant in that the flower stalk bearing the ovary burrows into the ground, where a nut containing the seed or seeds develops.
Groundnuts contain much more fat than other legumes, often 45 percent, and also much more niacin 18 mg per g and thiamine, but relatively little carbohydrate 12 percent. The protein content is a little higher than that of most other pulses 27 percent. Groundnuts are an unusually nutritious food with more protein than animal meat. They are energy dense because of their oil, and they are rich in vitamins and minerals. As suggested in Chapter 9, if every child, woman and man in Africa ate a handful of groundnuts per day in addition to their normal diet, Africa would be rid of most existing malnutrition.
Groundnuts are fairly widely grown in the tropics. Farmers should produce them for home consumption as well as for cash crops, since they form a very useful addition to the primarily cereal or root diets of many poor families. They supply much-needed fat, which is high in energy and assists in the absorption of carotene as well as serving other functions. In predominantly maize diets, relatively small quantities of groundnuts, with their high content of niacin and also of protein including the amino acid tryptophan , can prevent pellagra.
When groundnuts are added to children's diets, their high protein and energy content serves to prevent protein-energy malnutrition. However, groundnuts are often grown mainly as a cash crop even in developing countries.
The world's largest producer is the United States. Groundnuts are usually utilized for oil extraction, and the residue, groundnut cake, is used for animal feed. In the United States a good proportion is consumed as peanut butter. In many countries groundnuts are consumed roasted, boiled or cooked in other ways.
Groundnuts, if damaged during harvesting or if poorly stored in damp conditions, may be attacked by the mould Aspergillus flavus. This fungus produces a poisonous toxin known as aflatoxin, which has been shown to cause liver damage in animals and to kill poultry fed on infected groundnuts.
It may be toxic also for humans and may be a cause of liver cancer see Chapter The bambara groundnut Voandzeia subterranea originated in Africa and is grown widely.
It resembles the groundnut physically but is not nutritionally similar, having only 6 percent fat. Its protein content of 18 percent is a little lower than that of most other pulses, but it has about the same mineral and vitamin content as beans. Because of the lower fat content the crop is not in great demand for oil production.
Therefore, instead of being sold as a cash crop, it is more often used locally for food. Coconut is the most important nut crop in Africa. Its origins are uncertain. The nut, being light and impervious to water, no doubt drifted across many seas to germinate on a new shore. It is now extensively cultivated.
The tree that bears it is a picturesque and highly useful plant, apart from the food it provides for humans. When it is green, the nut contains about half a litre of water; this is a very refreshing and hygienic drink, but apart from a little calcium and carbohydrate, it has no nutritive value.
The white flesh, however, is rich in fat. The flesh of the coconut is usually sun-dried into copra. The oil from copra is used both for cooking and for making soap. Copra itself is used in the tropics and elsewhere as an addition to many dishes.
It is an important ingredient in a variety of cuisines from Thailand to Saudi Arabia. Coconut oil has the disadvantage of containing a relatively high proportion of saturated fatty acids. The coconut sap in many countries is fermented to yield alcoholic beverages.
The cashew nut is produced on a small tree that originated in dry areas of the Americas. It is widely grown in the tropics, and the nuts are mainly exported. They are rich in fat 45 percent and contain 20 percent protein and 26 percent carbohydrate. The edible swollen stalk of the nut contains good quantities of vitamin C. Cashew nuts are a useful local food but too expensive for most people. Sesame, or simsim benniseed in West Africa , is grown fairly widely throughout the world and is largely used for oil extraction.
The seeds, which are of various colours, contain about 50 percent fat and 20 percent protein. They are also rich in calcium and contain useful quantities of carotene, iron and B vitamins. Sesame seeds can form a nutritious addition to the diet.
Sunflowers are grown mainly as a cash crop, but some of the seeds and some of the oil are eaten locally. The oil has the advantage of being relatively high in polyunsaturated fatty acids. The seeds contain about 36 percent oil less than sesame , 23 percent protein and some calcium, iron, carotene and B vitamins.
The product from oil-palm Elaeis guineensis is discussed in Chapter 30 with other oils and fats. A number of other oil-rich seeds are eaten or used for oil extraction. These include pumpkin seeds, melon seeds, oyster nut Telfairia pedata and cottonseed. The last is a major source of oil in the cotton-growing areas of Asia, Africa and Latin America.
In West Africa and elsewhere, shea butter Butyrospermum parkii , butternut and several other oilseeds are used in the diet. Most of these grow on indigenous trees. The foods called vegetables include some fruits e. Many of the plants from which these various edible parts are taken are unrelated botanically. However, "vegetable" is a useful term both in nutrition and in domestic terminology. In developing countries, nearly all types of vegetables are eaten soon after they are harvested; unlike cereals, tubers, starchy roots, pulses and nuts, they are rarely stored for long periods with a few exceptions such as pumpkins and other gourds.
It is not uncommon for rural people in parts of Asia, Latin America and Africa to forage for an important proportion of the vegetables they consume. With increasing population, however, the availability of wild fruits and vegetables is decreasing. Therefore vegetables are obtained from the farm or the household garden or from the marketplace, neighbours or small stalls along the roadside.
When rural families with low income move to an urban environment they may resent having to purchase vegetables, because they are used to being able to gather wild ones or grow their own. They may therefore spend relatively little on this component of the diet. In any case, vegetables are rarely a prestige food, and in few societies are they high on the list of food preferences. Vegetables are a very important part of the diet. They are nearly all rich in carotene and vitamin C and contain significant amounts of calcium, iron and other minerals.
Their content of B vitamins is frequently small. They usually provide only a little energy and very little protein. A large proportion of their content consists of indigestible residue, which adds bulk or fibre to the faeces.
In many tropical diets the dark green leaves are the most valuable vegetables because they contain far more carotene and vitamin C, as well as more protein, calcium and iron, than pale green leaves and other vegetables. Thus amaranth is much superior to cabbage or lettuce. Leaves from pumpkin, sweet potato and cassava plants, as well as many wild edible leaves, are also excellent. An increase in the consumption of green leaves and other vegetables could play a major part in reducing vitamin A deficiency, which is often prevalent in children, and could contribute to lessening the prevalence of iron deficiency anaemia in all segments of the population but especially in women of child-bearing age.
Increased vegetable consumption would also supply additional calcium and vitamin C which would prevent the rare disease scurvy and perhaps also assist the healing of ulcers and wounds. Vitamin C also enhances iron absorption.
It is not possible here to describe the individual properties of the many vegetables commonly eaten in developing countries. A few, such as pumpkins, can be stored for several months with little loss of nutritive value; others, such as leaves and even tomatoes, are frequently sun-dried, but with considerable loss of vitamin content.
The vitamin C content of vegetables is also lowered by prolonged cooking. Vegetables grown in home and school gardens could be a valuable source of food for the family and the school and could make an important nutritional contribution, particularly to micronutrient intake. Home gardens can be raised with spare family labour and the participation of women and children.
It is therefore important for most rural households and virtually every school to devote more time to growing vegetables. A community garden near the village source of water is often a useful adjunct to the villagers' own backyard gardens. In towns, even the smallest piece of land behind a house could, with the assistance of waste water, yield a valuable supply of vegetables all year round. The allocation of allotment plots for vegetable growing deserves serious consideration by town councils and other urban authorities.
Even people living in flats can grow certain varieties in pots kept on their verandas. A wide variety of fruits grow wild or are cultivated in tropical countries. The varieties available at any one time in a given area depend on the climate, the local tastes for fruit, the species cultivated and the season. The main nutritive value of fruits is their content of vitamin C, which is often high.
Some fruits also contain useful quantities of carotene. Fruits except the avocado and a few others contain very little fat or protein and usually no starch. The carbohydrate is present in the form of various sugars. Fruits, like vegetables, contain much unabsorbable residue, mainly cellulose. The citrus fruits, such as oranges, lemons, grapefruits, tangerines and limes, contain good quantities of vitamin C but little carotene.
In contrast, papayas, mangoes and Cape gooseberries Physalis peruviana contain both carotene and vitamin C. Papayas are a useful fruit, especially for those who cultivate a piece of land for a few years and then move on to new land. The papaya grows rapidly and may yield fruit after one or two years. The mango, on the other hand, grows slowly, but once established and it may establish itself needs no care and yields fruit for half a century. Guavas, which are quite widely grown, contain five times as much vitamin C as most citrus fruits, as well as useful amounts of carotene.
The avocado requires special mention because, unlike other fruits, it is rich in fat, a substance that is lacking in many tropical diets. It could with benefit be much more widely grown and eaten and fed to children. Bananas are widely grown and eaten in tropical countries. They contain fair quantities of carotene and vitamin C, and they are rich in potassium.
In East Africa plantains or bananas are commonly picked when green. Cooked and eaten as a mainly starchy food, they form the staple diet of many people. When bananas are ripe their starch is converted into other sugars. A few fruit-trees would be a useful addition to all households, both urban and rural. Foods of animal origin are not essential for an adequate diet, but they are a useful complement to most diets, especially to those in developing countries that are based mainly on a carbohydrate-rich staple food such as a cereal or root crop.
Meat, fish, eggs, milk and dairy products all provide protein of high biological value, which is often a good complement to the limiting amino acids in plant foods consumed. These products are also rich in other nutrients. The iron provided by meat and fish is easily absorbed and enhances the absorption of iron from common staple foods such as rice, wheat or maize.
However, foods of animal origin are usually relatively expensive and not within the purchasing power of poorer families. Some wealthier people in both developing and industrialized countries consume large quantities of these foods; in consequence their intake of fat, especially saturated fat, may become excessive, increasing the risks of heart disease and obesity. Americans consume about 80 kg of meat per person per year - almost 0. Meat is usually defined as the flesh mainly muscles and organs for example, liver and kidneys of animals mammals, reptiles and amphibians and birds particularly poultry.
Meat is sometimes subdivided into red meat from cattle, goats, sheep, pigs, etc. The animals providing meat may be domesticated or wild. The amount of meat consumed often depends mainly on cultural factors, on the price of meat in relation to incomes and on availability. Meat contains about 19 percent protein of excellent quality and iron that is well absorbed.
The amount of fat depends on the animal that the meat comes from and the cut. The energy value of meat rises with the fat content. The fat in meat is fairly high in its content of saturated fatty acids and cholesterol. Meat also provides useful amounts of riboflavin and niacin, a little thiamine and small quantities of iron, zinc and vitamins A and C.
Offal the internal organs , particularly liver, contains larger quantities. Offal has a relatively high amount of cholesterol. In general all animals - wild and domestic, large and small, birds, reptiles and mammals - provide meat of rather similar nutritional value. The main variable is the fat content. Worldwide, a vast range and variety of animal products are eaten. Not all of them are popular everywhere, of course.
Certain foods that are popular in some parts of the tropics and East Asia - such as locusts, grasshoppers, termites, flying ants, lake flies, caterpillars and other insects; baboons and monkeys; snakes and snails; rats and other rodents; and cats and dogs - are not found in European or North American diets. Similarly, the French liking for frogs' legs and horse meat and the English and Japanese taste for eels and raw oysters are not shared by many people living elsewhere. Liked or disliked, however, all these foods are nutritious and contain protein of high biological value.
Contaminated meat can lead to disease. There is a need for improvements in conditions associated with production of meat both for local or family consumption and more importantly for commercial sale. For meat to be safe for human consumption, hygienic practices are essential at all levels, from the farm, through the slaughterhouse, to the retailer and into the kitchen.
Most countries have regulations governing meat hygiene and authorities responsible for applying the regulations, but their effectiveness varies widely. Fish and seafoods, like meat, are valuable in the diet because they provide a good quantity usually 17 percent or more of protein of high biological value, particularly sulphur-containing amino acids.
They are especially good as a complement to a cassava diet, which provides little protein. Fish varies in fat content but generally has less fat than meat. Fish also provides thiamine, riboflavin, niacin, vitamin A, iron and calcium. It contains a small quantity of vitamin C if eaten fresh. Small fish from the sea and lakes such as sardines and sprats dagaa in the United Republic of Tanzania, kapenta in Zambia are consumed whole, bones and all, thus providing much calcium and fluorine.
Dried dagaa, for instance, may contain 2 mg calcium per g. Fish offal is not usually consumed as part of any diet anywhere. However, fish liver and fish oils are very rich sources of the fat-soluble vitamins A and D. The amount varies, usually with the age and species of fish. Wherever water is available, fish provide a simple way of increasing protein consumption. The stocking of dams, the construction of fish ponds and better and more widespread fishing in rivers, lakes and the sea should all be given greater encouragement.
There is much regional variation in the variety of sea creatures people will eat. Encouraging children in coastal districts to collect sea urchins, sea slugs, limpets and the numerous other edible sea creatures, just as inland children collect locusts and lake flies, would considerably improve poor diets.
The introduction of swimming lessons in youth clubs and as a community development activity would encourage development of this pastime as well as fishing both for pleasure and for profit; fear of the water because of inability to swim is a deterrent to these activities, particularly among people who do not live beside water.
The egg is one of the few foods containing no carbohydrate. Just as the foetus in the mother's uterus draws nutrients from the mother's blood in order to grow and develop into a human being, so the bird embryo draws all its nutrients from within the egg. It is not surprising therefore that eggs are highly nutritious. Each egg contains a high proportion of excellent protein, is rich in fat and contains good quantities of calcium, iron, vitamins A and D and also thiamine and riboflavin.
Eggs are an essential part of the reproductive cycle of birds, so it is hardly surprising that their consumption, particularly by females, is forbidden by taboos in many societies. The irony is that eggs are often more easily available than most other high-quality foods. In developing countries it is not often that a family can afford to kill a cow or even a goat for food, but eggs are small and frequently laid.
They are also an easily prepared, easily digestible, protein-rich food suitable for children from the age of six months onward. Eggs do have a nutritional disadvantage: The cholesterol is present in the yolk.
Production of eggs for family use should be encouraged wherever possible, even in the small garden or yard of an urban dwelling. Toddlers should be given priority in eating the eggs.
Cattle blood, which is regularly consumed raw by many pastoral peoples, particularly in Africa, is highly nutritious. It is rich in protein, has high biological value and contains many other nutrients.
It is a particularly valuable source of iron. It is also a good source of nutrients in its processed form, usually a type of sausage. Animal milks and other dairy products are highly nutritious and can play an important part in human diets for both children and adults.
The composition of milk varies according to the animal from which it comes, providing the correct rate of growth and development for the young of that species.
Thus, for human infants, human milk is better than cows' milk or any other milk product. Exclusive breastfeeding without other foods or liquids is the optimum means of feeding for the first six months of an infant's life see Chapter 7.
Continuing breastfeeding for many more months is of great value, while the baby is introduced to other foods. If breastmilk remains an important food for the child into the second or even third year of life, then animal milk is not necessary in the child's diet.
The composition of human and cows' milk is compared in Chapter 7 Table 7. Except for certain vitamins, the composition of human breastmilk is fairly constant, regardless of the diet of the mother.
Maternal malnutrition will not cause a mother to produce milk of markedly lower nutrient content, but it will reduce the quantity she can produce. A few nutrients such as thiamine and vitamin A may be low if mothers are deficient in these nutrients. Caseinogen and lactalbumin, proteins of high biological value, are among the most important constituents of cows' milk. The carbohydrate in cows' milk is the disaccharide lactose. Fat is present as very fine globules, which on standing tend to coalesce and rise to the surface.
The fat has a rather high content of saturated fatty acids. The calcium content of cows' milk mg per ml is four times that of human milk 30 mg per ml , because calves grow much more quickly and have a larger skeleton than human babies and therefore need more calcium.
When a human infant is fed entirely on cows' milk the excess calcium does no good but causes no harm. It does not produce a rate of growth beyond the optimum. The excess is excreted in the urine. Milk is also a very good source of riboflavin and vitamin A. It is a fair source of thiamine and vitamin C, but it is a poor source of iron and niacin. The mother usually provides her infant with a store of iron before birth. However, this store is exhausted by about the sixth month of life, and if feeding of milk alone is prolonged, iron deficiency anaemia may develop.
The amount of thiamine in human milk varies more than the other constituents and is largely dependent on the mother's intake of this vitamin. Infantile beriberi may occur in infants breastfed by thiamine-deficient mothers. The vitamin A content of human milk is to some extent dependent on the diet of the mother. Despite the variation in the composition of milk from different animals, all milk is rich in protein and other nutrients and constitutes a good food for humans, especially children.
Although most animal milk for human consumption comes from cows, in certain societies the milk of buffaloes, goats, sheep and camels is important. Some peoples have taboos against milk. In many parts of the world, milk is more often consumed sour or curdled than fresh; in fact, some people dislike fresh milk.
There is no need to alter this habit, for curdled milk keeps longer, retains its nutritive value and may be more digestible and more hygienic than fresh milk. However, it is much safer to drink milk that has been boiled and kept in a clean container, because milk can provide a vehicle for the transmission of some disease-causing organisms.
Pasteurization of milk carried out efficiently in a large, well-run dairy greatly reduces the risk of pathological organisms spreading, provided that the milk is placed in clean containers destined for direct delivery to the consumer.
However, in many small towns where pasteurization is not well controlled, the milk may be insufficiently heated, the containers may not be well cleaned, and the milk may go from the plant into large churns for bottling elsewhere in insanitary surroundings. The consumer should not be overconfident in all milk labelled "pasteurized", since it is not necessarily free from pathological organisms. In many countries where cows' milk is a normal item of the diet, it is customary to wean infants from breastmilk on to a diet in which cows' milk plays an important part.
This is a valuable practice, for it helps ensure that the child will receive a balanced diet that provides all the requirements for growth, development and health. Some people limit their milk consumption because of lactose intolerance, a condition resulting from low levels of the digestive enzyme lactase, which is responsible for digesting lactose, the main carbohydrate in milk. It is probably normal for human adults to have low levels of intestinal lactase, and the condition is very common in non-white peoples.
Research shows that most lactose-intolerant persons can in fact consume milk in moderate quantities perhaps three to five cups of milk per day without developing symptoms.
Skimmed milk is milk from which the fat has been removed, usually for making butter. In its dried form DSM , it is a familiar product in many countries.
It contains nearly all the protein of milk, as well as the carbohydrate, calcium and B vitamins. It is an excellent food, especially for those on predominantly carbohydrate diets and those who have extra needs for protein. In some places DSM is supplied to those with special needs through clinics and health centres. It is extensively used in hospitals and dispensaries as the basis for the treatment of protein-energy malnutrition PEM.
It is also issued at child-welfare clinics to prevent this most devastating form of malnutrition. Skimmed milk is an excellent food to add to any diet, but it is particularly useful in the diets of children and pregnant and lactating women. However, it is not a suitable substitute for whole milk for infants. This product, as the name implies, is whole milk that has been dried. Unlike DSM, it contains fat. It is suitable for infants when no breastmilk is available.
These are milks that have had much of their water removed but that are still liquid. Condensed milk is sweetened by the addition of sugar, whereas evaporated milk does not contain added sugar. Many brands of condensed milk have vitamins added. These brands should be preferred to those that do not have vitamins added, especially if they are used in the diets of young children.
They are not suitable as breastmilk substitutes for infants. Many different organisms are used in the process of making yoghurt and fermented milks. These products are easy to prepare, are highly nutritious, have enhanced keeping quality and are a little less likely than fresh milk to harbour pathogenic organisms. Their use should be encouraged. Casein is the protein from milk. It tends to be rather expensive. It is commonly mixed as part of a formula or mixture for treatment of children with PEM see Chapter The making of cheese no doubt arose from the desire of farm people to preserve some of the excess milk of the summer.
Numerous processes are used, but essentially cheese is made by letting milk clot and subsequently removing some of the water. Salt and other flavourings may be added. Cheese-making is an excellent way of using any excess milk produced during the seasons when milk yields are high.
Butter and ghee are both milk products, but being mainly fat they are discussed in Chapter 30, "Oils and fats". In general adults should consume at least 15 percent of their energy intake from dietary fats and oils, and women of childbearing age should consume at least 20 percent. Active individuals who are not obese may consume up to 35 percent and sedentary individuals up to 30 percent of energy from fat as long as saturated fatty acids do not exceed 10 percent of the energy intake and cholesterol intake is limited to mg per day.
Annex 1 gives levels of fat intake for low-income countries calculated according to the recommended range 15 to 35 percent of dietary energy from fat. Infants fed human milk or formula usually receive 50 to 60 percent of their total energy from fat. Infants should receive breastmilk, but if they do not, the fatty acid composition of infant formula should correspond to the range found in the breastmilk from omnivorous women.
During complementary feeding up to two years of age or beyond, the diet should provide 30 to 40 percent of energy from fat. To achieve the recommended levels of fat intake, poor people, particularly in developing countries, would need to increase their intake of fat and oils.
In contrast, most people living in rich industrialized countries would need to reduce their consumption of fat and oils, which now often provide 40 percent or more of the energy they consume. The fat consumed in human diets is often divided into two categories: Persons in developing countries who may get only 15 percent of their energy from fat will often obtain two-thirds as invisible fat and one-third as visible fat or fat added to food.
In contrast, in North America and Europe, where mean intakes of fats are high, some 70 percent may be visible fat and 30 percent invisible fat. A diet very low in fat tends to be unpalatable and dull. It is difficult to cook a really good meal without any fat or oil, although the desired amount is largely a matter of habit and taste. However, like animal proteins, fats are relatively expensive, so the diet of poorer people is often short of fat. Fat is important because weight for weight it provides more than twice as much energy as carbohydrate or protein, thus reducing the bulk of the diet.
Fats and oils may be good sources of fat-soluble vitamins, and they assist with the absorption of other nutrients.
Recent work has established that certain unsaturated fatty acids are essential for pre- and postnatal development of the brain in children and are also essential for health in adults. Fats contain a variety of fatty acids.
Fats derived from land animals e. Fats derived from vegetable products and marine animals e. Coconut oil is an exception in that it contains mainly saturated fatty acids. A high intake of saturated fatty acids may contribute to raised serum cholesterol levels, which in turn may increase the risk of coronary heart disease. Butter consists mainly of the fat from milk.
It usually contains about 82 percent fat, with a trace of protein and carbohydrate; the rest is water. Butter is rich in vitamin A and has a small amount of vitamin D, but the content varies with the time of year and the diet of the cow from which it was derived.
Usually about mg of retinol and 50 IU of vitamin D are present in g of butter. Butter and margarine are increasingly used in diets in developing countries as the use of bread increases. Developed as a substitute for butter, margarine is made from various vegetable oils that are partially hydrogenated to give a product with a consistency similar to that of butter. In most countries vitamins A and D are added so that the final product is nutritionally very similar to butter.
If these vitamins have been added, they will usually be mentioned on the margarine container. Ghee is made by heating butter to precipitate the protein, which is then removed. Ghee contains 99 percent fat, no protein or carbohydrate, about 2 IU of vitamin A per g and some vitamin D.
It has good keeping qualities and is much used in tropical countries in place of butter, because butter soon goes rancid if kept unrefrigerated in warm temperatures. Lard is collected during the heating of pork. Like other similar animal fats e. Vegetable oils are the cooking fats most commonly used in Africa, Asia and Latin America, and there are many different kinds.
Except for red palm oil, they have the disadvantage of containing no vitamins except vitamin E. They are mainly low in saturated fatty acids. Commonly used vegetable oils are soybean, olive, maize, groundnut, sunflower, sesame, cottonseed and coconut oils. In their pure form, they are percent fat and contain no water or other nutrients. Red palm oil is widely produced in West Africa and in certain Asian countries e.
In West Africa it is important in human diets, but elsewhere it is exported for soap production and not much consumed locally. It is therefore a very valuable food wherever a shortage of vitamin A occurs in the diet. Vitamin A deficiency will not be a problem in areas where all members of the family consume even small quantities of red palm oil.
Encouragement should be given to its wider cultivation and consumption. It is essential that the human body receive water, yet the human taste prefers that much of this water be obtained in the form of beverages. These include beer, wine, spirits, fruit juices, tea, coffee, cocoa, synthetic sweetened soft drinks and aerated waters. Some of these beverages contain small amounts of drugs such as caffeine tea, coffee and some colas or alcohol in varying amounts beer, wine and spirits , and some are sources of minerals and vitamins.
In most countries there are traditional beverages of great variety. In Africa many of these are made from cereal grains that have been soaked and sprouted. These beverages may or may not be alcoholic, and some are useful sources of B vitamins.
In other parts of the world local beverages may be made from honey or coconut or any number of local products. In the industrialized countries aerated soft drinks, often called "sodas", many with a cola base, are highly popular and consumed in huge quantities.
In many parts of Africa, Asia, Latin America and the Near East, manufactured soft drinks and sodas are replacing traditional beverages. Most of these sodas provide no significant nutrients other than carbohydrates. In contrast, fruit juices, either purchased or home-made from fresh fruit, usually contain useful amounts of vitamin C, and some provide carotene.
They are good beverages, especially for children. It is not uncommon to find mothers giving their babies and children orange squash or fruit-flavoured sodas because they were told at the clinic to give them fruit juice. These manufactured beverages are no substitute for fruit juice and will do the child no good; they are simply a waste of money. Certain vitamin-rich proprietary beverages have been designed for infants and children. Their vitamin content is nearly always clearly stated on the label.
They need to be used with caution, however. They are not necessary if the child is getting fresh fruit and vegetables, and they are often a very expensive way of providing vitamin C to a child. The advertising promoting them is pervasive, however, and can persuade mothers that they are useful.
Another major group of beverages comprises those usually consumed hot. Tea, which was probably first drunk in China, is now the favourite beverage of many people in Africa, the Near East and Europe. The two main types are Arabian, Coffea arabica, and robusta, Coffea canephora.
In all regions of the world tea, coffee and to a lesser extent cocoa are popular beverages. All three provide small amounts of caffeine, which is a mild stimulant. None have any great nutritional significance. Tannin and polyphenols in tea may reduce iron absorption. For thousands of years people from all continents have produced beverages that contain ethyl alcohol. Usually certain yeasts are used to ferment a local carbohydrate-rich food for example, cereals or root crops , but fruits, palm sap, honey and other raw ingredients are also used.
In the industrialized countries beer often made from barley , wine made from grapes and various spirits drinks with a relatively high alcohol content made by distillation are very widely consumed, and this practice has spread to many countries of the South. Alcohol produces a good feeling for many who drink it, but it also impairs the senses, and it can be addictive.
It can be claimed that alcohol consumed in moderation provides a sense of well-being and may improve social interaction; but alcohol in excess is a serious cause of automobile and other accidents, and alcoholism is a highly prevalent and very damaging disease in all continents of the world.
Animals and primitive men and women obtained most of their fluids in the form of water; then for thousands of years other beverages became the favourite drink for humans; and now there is almost a craze to drink "natural" or "spring" waters, either aerated or still. Many consumers believe that these waters, coming from springs, lakes, rivers or wells, have near-magical qualities and great nutritive value. This idea is false.
Bottled water may contain small amounts of minerals such as calcium, magnesium and fluoride, but so does tap-water from many municipal water supplies. A study comparing popular brands of bottled water showed that they were in no way superior to New York tap-water. They have only the advantage of being safe in areas where tap-water may be contaminated. However, for low-income people bottled waters are very expensive, and boiling local water renders it safe at a much lower cost.
Salt consists mainly of sodium chloride. It is the only mineral salt that humans customarily consume in a chemically pure form. The body has a definite need for sodium and chlorine.
The amount of sodium chloride in the body is regulated by the kidneys. In hot countries a person doing heavy work may lose 15 g of sodium chloride in body sweat in one day. Urinary excretion ranges from 1 to 30 g or more per day. Despite this loss, salt is not essential in the human diet unless sweating is profuse, because sufficient sodium and chlorine can be obtained from food alone. Nevertheless, nearly all people use salt, obtaining it by digging, making or buying it, however small the income.
Certainly a salt-free diet is unpalatable. Adults usually consume about 10 g of salt a day, but there are enormous variations. A high intake of salt may contribute to the development of hypertension or high blood pressure in some individuals.
Other spices and flavourings are of less physiological or nutritive importance. In all countries, in all ages, people have added such items to their food to improve and vary its taste.
In Africa, Asia and Latin America a variety of wild leaves are used, partly for flavour, partly as vegetables per se; hot chilies, both red and green, are frequently used; and pepper and curry powder are popular additions to the sauce or stew accompanying the staple food. Few of these flavourings have much nutritional importance, but all serve to make the food more pleasing to the taste. They therefore both increase the appetite and assist digestion by stimulating the secretion of saliva and intestinal juices.
With the march of so-called civilization, many of the traditional and natural condiments and herbs are being replaced by proprietary sauces and flavourings. Some of these are artificial chemical agents for example, monosodium glutamate and some are based on traditional spices garlic, cloves, ginger, etc. Humans are unique in the animal kingdom in that they harvest, store and process food that they have grown.
Almost all animals harvest food, and many animals store it for later consumption, but they do not grow it or process it. In their evolution from the apes humans learned to grow food for their own sustenance and then to develop many processes to preserve the food or to increase its desirable characteristics, sometimes thus decreasing or improving its nutritional value.
People seek to preserve food and to improve its quality using a variety of techniques such as drying, canning, pickling, adding chemical preservatives, refrigeration, freezing and irradiation.