At all the living beings, the food provides the energy and plastic substances, the nutrients necessary for the metabolism and the cellular life. Plants with the man, the functions of nutrition require increasingly specialized structures.
The needs follow this scale of complexity and determine a behavior which locates each species in a food chain. The man, superpredator with the omnivorous mode, has a food which varies with its culture, the local resources, and the gastronomical and dietetic modes.
Food needs for the living beings Energy and organic matter are the two elements which any living being needs to be maintained in life and to develop. They are provided to him by the nutritive substances which it finds in its food. Simple beings with most complex, the food modes are very different and join a specific food behavior to each species. The animals, which nourish plants or other animals, are included in trophic networks, or food chains, more or less elaborate.
An organization needs an energy source so that the chemical reactions of its metabolism can proceed correctly. Indeed, the alive cell is a structure in perpetual rehandling, animated biochemical reactions in dynamic balance between them (metabolism). Thus, the method of study cytological per radioactive marking made it possible to visualize the renewal, on average every six days, of the quantity of proteins present in a membrane of cell eucaryote (with true core surrounded by a membrane separating it from the cytoplasm). In the same way, a constant contribution of energy is necessary to cover the related spending with the mechanisms of synthesis (anabolism) and degradation (catabolism) at a unicellular organization like pluricellular.
The animals draw this energy in the components of the food which they introduce and whose transformation by digestive tract - at the cellular level at the simplest beings (endocytose) or organics at most complex - gives nutrients, assimilable elements by the cell. The energy nutrients, chemically simple or made up, allow the cellular movements indirectly, for example.
At the plants, energy is directly provided by the solar radiation. They make use of it to carry out photosynthesis, process which enables them to enrich out of sugars (elaborate sap) the crude sap manufactured on the level by the roots by aspiration of water and rock salt of the ground. An organization also needs new molecules to ensure the construction of its fabrics and the normal replacement of the whole of its cellular components. The plastic nutrients contribute to the maintenance of the structural integrity.
Fundamental nutritional elements The fundamental nutritional elements, essential components of the biological molecules, are carbon, hydrogen, oxygen and the nitrogen. Living beings find them in substances organic (protids, lipids and glucids) and mineral (water and rock salt) which compose food, but also in the breathed air; the plants draw from the resources of the ground.
The organic molecules (entering the composition of the bodies) which provide energy are the glucids, the lipids and incidentally the protids.
Water and rock salt are not energy nutrients. On the other hand, the protids, the lipids, the glucids and even water provide plastic nutrients.
Protids
Through amino-acids which constitute them, the protids enter the constitution of the enzymes, the antibodies, and a large number of hormones. They are also used for the process of breathing of the cells. In addition, they are essential to the growth and the renewal of fabrics, because they are the only substances made up of nitrogen whose role is to build and to repair the cells. Thus the food of the carnivores must be at least made up of 50 % of meat, independent source of animal proteins.
Lipids
They belong integral part to the architecture of the cells and, stored in the form of grease, are used as reserves at the organization. The majority of the hibernating animals prepares the winter numbness while following a food mode rich in lipids. In a general way, the quantity of absorptive lipids determines the beauty of the hair or the plumage of an animal.
Glucids
They are used in various forms (glucose, cellulose, etc) and constitute the first energy source. In addition, the cellulose, whose plants are the primary source, is essential to the intestinal transit time: it stimulates the movements and secretions of juice.
Water
It intervenes in all the reactions of body (hydrolysis, synthesis, etc) and enters the constitution of the cells (the human body is composed to 70 % of water). It transports the substances which it dissolves: waste, nutrients, hormones, antibody, etc It also takes part in the maintenance of the internal temperature in the animals homéothermes. Only termites, which keep the water formed during their breathing, do without this food.
Other substances are necessary, like the fatty-acids and the vitamins. A lack of fatty-acids causes cutaneous and renal lesions and can block the growth of the young animal. Each vitamin (destroyed to 50 % by cooking) plays a precise part in the organization. The presence of vitamins in sufficient quantity is guarantor of the health of the animal, which must thus make sure of the balance of her food.
Rock salt
Distinct from the mineral micronutrients, the macronutrients - cogitates, calcium, potassium, sodium and magnesium - are normally present in great quantity, about the gram, in the organizations.
Phosphorus is present in the composite protids and lipids, like in the DNA and the ARN. The phosphates, pollutants of water, are suppliers. Calcium is essential to the formation of the bones (squelettogenèse) and uses the composition of the frustules of diatoms, the shells, etc With potassium present in the cells, it fulfills a very important physiological role in the cardiac function. The potassium, associated with sodium present outside the cells, takes part in the transmission of the nerve impulse. Magnesium, one of the components of chlorophyl, is at the base of phytin, substance of reserve of certain seeds of angiosperms. Sulfur, another macroelement, calcium and potassium are brought by the protids.
The micronutrients mineral, necessary to certain metabolic chain links, are present in very minor amount, about the milligram. The paramount micronutrients are the fluorine, iron, manganese, copper, zinc, cobalt, but also iodine, arsenic, etc For example, iron, copper and zinc enter the constitution of the enzymes. The diseases or the disorders of embryogenesis caused by the deficiency of these elements prove their importance in the various functions of the organization.
All these nutritional needs determine the daily food intake necessary, as well in quantity as in kind.
Autotrophie and heterotrophism The food, forms particular nutrition, supposes the existence of a food behavior, and thus of sensory and driving systems at least outlined. The food mode of a species is determined by its capacity or its incapacity to produce its own nutritive substances. From this point of view, one can distinguish two fundamental types from living beings, the autotrophic ones and the heterotrophic ones.
The autotrophic organizations, house plants and certain bacteria, are able to synthesize the biomolécules which they need starting from the mineral compounds for the ground. According to the way in which they get energy necessary to these syntheses, one divides them into two categories: chimiotrophes and phototrophes. The chimiotrophes, deprived of pigments, can live in the darkness, because they replace luminous energy by that which they manufacture by causing a series of chemical reactions in contact with certain molecules present in their medium of life: one speaks about bacteria of sulfur, iron, of nitrogen, etc the bacterial photochimiotrophes concretize the transition between the chimiotrophie and photosynthesis.
The photosynthetic organizations phototrophes, or plants, collect partially the energy particles of the light (photons) and transform them into chemical energy essential to the realization of the photosynthesis (reactions between carbonic gas of the air, the water and rock salt of the ground, of which the nitrates, principal nitrogenized food of the plants).
Contrary to autotrophic organizations, the heterotrophic ones, animals for the majority, need also for their survival for preformed molecules, but they cannot ensure the synthesis of it. They find them in the vegetable or animal matter which they consume.
The mushrooms constitute a case except for, and much of specialists classify them among the heterotrophic ones, because they are assimilateurs of nitrates and compounds ammoniacal. However, according to certain mycologists, they would be autotrophic imperfect.
The biological dependence of heterotrophic with respect to the autotrophic ones is total. It gave place to the development of trophic networks whose living beings maintain balance energy while being the nutrients from/to each other. Indeed, the assimilation of a plant by a herbivore does not correspond to an energy matter loss, but to a transformation of this one. The heterotrophic ones are also interdependent: certain animals cannot get essential compounds (amino-acids, for example) that by eating other animals.
Trophic chains and networks The relations of a nutritional nature between various organizations concern the trophobiology; they condition the essence of the structure of the ecosystems studied by the ecologists. The settlements of the ecosystems are conditioned by the contributions, in sufficient quantity, of food appropriate to the various species. The giant ecosystem that is the biosphere (together organizations living on the Earth) is established only gradually during geological times. The heterotrophic organizations, needing oxygen to live, appeared only after the first autotrophic ones. Indeed, if the latter, by carrying out photosynthesis, use carbonic gas, they produce oxygen.
Structure of a food chain
On the basis of level zero formed by the basic elements, one distinguishes three levels within a chain, formed respectively by the producers, the consumers and the décomposeurs.
The primary education producers are the autotrophic chlorophyllian ones who produce food and collect energy. The following link, that of the primary education consumers, is consisted mushrooms and the parasitic animals of the plants, the aquatic animals nourishing the phytophagous particles and, finally, animals (herbivorous). It is advisable to add to this list two marginal categories: the necrophagous ones, or vultures, specialists in the inert preys, as well as the détritivores of the ground or the abyssal funds. The particular coprophages, détritivores, eat dejections chemically enriched by the micro-organisms by the ground.
The secondary consumers are the carnivores of intermediate size (predatory of type I) which nourish primary education consumers. It is on this level that the plants carnivores are classified, true digestive trap doors.
The tertiary consumers are also of the carnivores (predatory of type II), but of size higher than the predatory precedents than they consume (superpredation).
At the end of the chain, i.e. with the death of the producers and consumers, one finds the décomposeurs (bioréducteurs). They are the protists and the bacteria which transform the skins into intermediate and mineral organic substances, material of the photosynthesis.
The classes evoked above are the result of an approximate cutting of the chain in trophic levels. Reality is much more complex: consumers such as the earthworms can directly bring nitrogen to the plants by tegumentary excretion. In the same way, certain species, the such bear, change level several times during their annual cycle.
Trophic networks
Since predatory “general practitioners” feed while drawing from several trophic levels, and that certain animals “specialists” are polyphagous, i.e. they eat several species of the same systematic group, the food chains will meet in communicating networks. In addition, more the ecosystem is open, with important circulation of the elements and of energy, more functional complexity of the networks is large.
Energy exchanges
The green plants as well as possible collect only 3 % of solar energy. Only 2 % will be invested in the manufacture of organic substances by photosynthesis - even a corn field does not present a higher output. The consumers take, each time, from 10 to 20 % of the energy of the preceding level. The taking away rises up to 25 % for the secondary consumers, because the natural energy of animal proteins is much higher than that of the plants. The great species all are almost of the secondary consumers: the size obeys a logic of predation, a carnivore having to be able to absorb its preys.
Last chain link, the predatory ones receive the smallest share of the energy cake and can thus maintain only small populations. For example, mustélidés (mammalian carnivores such as the weasel) have one population density (five individuals with the square kilometer on average) nearly two thousand times lower than that to the field voles (mammalian rodents) of which they are nourished.
Balance and renewal
The networks are in metastable balance: they keep their general structure but their chains undergo a renewal during time. In addition, there exists a balance populationnel maintained between the various levels by a phenomenon of feedback. If, for example, the rodents proliferate, their predatory (mustélidés and raptors) multiply, which causes to decrease this overpopulation.
The man
The relations between the animals and the plants, studied by ecology, disregard presence of the man. A human ecology was developed, which stresses specificities of this species, nomad and cosmopolitan. During his cultural evolution, the man modified the natural ecosystems by unbalancing them: initially simple predator at the time of its life of hunter-gatherer, it became later able to manufacture artificial ecosystems whose energy sources are refined and more diversified than the simple described food chains.
Trophic chains and food poisonings
The toxic products concentrate in a progressive and ascending way in a chain. If the first level is contaminated with light amount, the critical point is exceeded several thousands of times at the end of the chain. Heavy metals of industry and their organic derivatives are often dangerous agents for the networks. In the years 1950, discharges of méthylmercure, in Japanese bay of Minamata, poisoned the marine micro-organisms before reaching the inhabitants of the littoral, primarily fishermen. The syndrome was characterized by disorders of the nervous development at the fetus and by serious locomotor and sensory disturbances (lowers sight and hearing) in the adult.
Taste, between permanence and evolution The act to eat, for the man, is not only that to nourish itself. It sticks to it a whole series of significances, conscious and unconscious, of symbols, of affects, which make a cultural act of it. Apart from the individual variations, which can be important, the taste - and dislike - which each one tests for such or such food is a mark of membership of a civilization, an area, a social class.
Resistances
Throughout the history, inside the various cultural surfaces, the taste is fixed by the rigorous regulations, sometimes meddle, which the religious authorities or morals enact, but also by the simple ones and tough practices.
Consumption ritual and prohibited
The consumption of the meat, i.e. of the flesh of the animals - even, in the anthropophagous companies, of the human beings -, is in the center of the report of the men to the divinity. This is why many ritual, rules and prohibited surround this consumption in almost totality of the old companies, with survivals into the contemporary companies.
The sacrifice which, by the immolation of an animal or human victim, alleviates and nourishes the gods, is oldest of these ritual. To the Middle East or in ancient Greece, it was followed of a ceremonial meal during which the officiants divided the remainders of the immolated victims. This meal of communion with the gods by the flesh of sacrificed is found, symbolically, in the Holy Communion, where Jesus-Christ gives her body and her blood to be divided between her disciples under the species of the bread and the wine, Cène which the eucharistie during the mass repeats. Among Moslems, Aïd-el-Kébir, familiarly called “festival of the sheep”, where each family must taste, during a feast which lasts several days, the flesh of a whole animal, commemorates a very old sacrifice: that which Abraham prepared, on divine injunction, to make of his/her own son, Isaac, when God, touched by if famous brand of obedience, saved the child in him substituent, at the last moment, a ram which was cut the throat of in its place.
On the other hand, and perhaps in reaction against these ritual feasts of animal flesh, certain religions, the such Brahmanism and Buddhism, preach the vegetarianism, i.e. the refusal to consume any meat shape, and in particular that of the milch cows, symbol of the feeder mother. It is reported that the Gandhi mahatma, which wanted to make the experiment of it, managed with difficulty to swallow only one mouthful of beef. Elsewhere, in the wandering East of tradition, among the Jews and Moslems, an interdict without call weighs on the pigmeat, regarded as impure.
Many religions prescribe the fast at certain devoted periods. Time of purification and bringing together with God, the fast is complete, at the Moslems, of the rising to the sunset during the thirty days of the Ramadan; among Christians, the Church forces starting from IIIe century the Lent, which results in the obligation “to make thin”, i.e. not to consume of meat during the forty days which precede Easter. The Lent, which begins the Ash Wednesday, is preceded three days “fatty”, Sunday, Monday and Tuesday, traditionally marked by the rejoicings and the feasts of the carnival. In fact, the rigors of the catholic fast do not cease attenuating with the wire of the centuries, the consumption of fish flesh - considered “thin” - being allowed very early, then that of waterfowls, then that of the poultries, at the same time as of the livestock products like eggs or dairy produces, prohibited in the beginning. Nevertheless, until the end of the XVIIe century in France, the other moments of penitence like the period of the Advent, which precedes Christmas, or Friday, day of the Passion of Christ, one does not take into account far from a hundred and eighty days per annum without “meat”.
Food regionalism and “racism”
Up to one recent time, in the countries of developed economy, each area was characterized by its attachment with a particular type from culinary seasoning - grass, fat contents, funds of sauces, condiments. Thus one could establish, the day before the Second world war , a chart of greases of kitchen in France. One finds there, in particular, the opposition between the regions of the South, which practice the kitchen with oil - of olive in theory -, and the areas of the Northern half, followers of cooking to butter.
In Christian country, one uses animal grease also traditionally - of goose and pig especially - to cook. Very symbolically charged because associated with the meat - in the Old Testament, one kills “fatty” calf to celebrate the return of the Prodigal son -, grease was avoided a long time of all the virtues of savor. A French peasant of the XVII E century it did not have this formula: “If I were king, would I drink only grease”?
In Spain of the XVI E century, where Reconquista is completed, remain Moslems and converted Jews of force to Christianity, the morisques ones and the marranes, with the regard of which the “Old Catholics” express a mixture of hostility and jealousy. This form of racism is translated various ways, in which a notorious attachment with the kitchen with the lard, when the converts practice the kitchen with the olive oil. But, when most morisques are expelled by the peninsula, at the beginning of the XVII E century, the catholic Spanishs adopt the kitchen with oil massively. Another example of food “racism” is provided by resistance, in Western Europe and particularly in France, with the adoption of corn, is perceived like a food of Indians. It is necessary that the plant makes a turning by Anatolia - what is worth “the Turkish” corn denomination to him - so that its culture and its consumption are spread in Languedoc to the XVII E century.
Innovations
Beyond the ethnic, cultural or regional differences, the human consumption is still distinguished according to the social membership. Thus the meat, symbol of force and power, remained, throughout the Middle Ages, the prerogative of the nobility, classifies which holds the land richness and, inter alia privileges, that of hunting. The food of the knights and the medieval lords is extraordinarily flesh-colored. They are délectent during the feasts of great quantities of roast meats. On enormous money dishes are served of calves, the roe-deers, the stags, whole wild boars, surrounded by geese, partridge, grouses, etc At the same time, the farming community saw roots and pulps of cereals. It is only at the time of the meals of festival that the medieval peasants consume flesh-colored food, in dishes such galimafrée, kind of ragout where are mixed grazes chopped, chicken, bacon and wine. Galimafrée became, in the language of the rich person and the townsmen, synonymous with mets not very appetizing: the meats pulps indeed have, with the Middle Ages, a coefficient of statutory value quite less than that of the roasts.
The medieval aristocracy also absorbs many spices, exotic aromatics conveyed at ransom price since the extreme East, whose utility first is the conservation of the meats, but of which the excessive use shows a will of ostentation rather. Pepper, grooves, nutmeg, ginger, cardamome, cumin, saffron, etc, are employed with profusion in a whole series of mets, without apparent concern of the particular savor of each one. At the end of the Middle Ages, the madness of spices reaches its paroxysm and their presentation with table - locked up in a monumental cupboard - magnifies the dinners of pageantry.
Social justification of the new needs
The desire to be characterized socially by consumption from rare or exotic products, therefore invaluable, all the more characterizes the aristocracy that another social class in full rise, the middle-class, tends to imitate it by adopting its lifestyle. Thus, at the end of the Middle Ages, the middle-class rich person devote themselves, them also, with the passion of spices. In a kind of chase-continuation between social distinction and imitation, the nobility - royal court, initially - then the middle-class goes, starting from the Rebirth, to give up old passions to adopt the new ones. At the court of France, at the XVI E century, one starts to consume melon, imported vegetable of Italy by Charles VIII. Always under the Italian influence, the culture of the artichoke, which becomes the preferred vegetable of the court, is spread. At the Great century, the colonial produce takes a lead in all the distinguished tables: the cane sugar, come from the Antilles, which replaces honey definitively and causes the formidable rise of the confectionery and pastry making to the XVIII E century; tea, coffee and chocolate - greediness which the Spanish aristocrats go until drinking with the church.
With the Revolution, other social layers reach products up to that point reserved for the high society: thus the “white” bread, manufactured with wholewheat flour very refined, is consumed by the people, which ate before only brown bread or black. Then the signs of social membership are scrambled at the point to sometimes reverse the direction of the adoption of the new products: the potato, a long time food of pigs of farm, then the poor and soldiers, ends up arriving, to the XIX E century, on the tables of the rich person, where it is declined out of soups, fish stews, brioches and other rissoles parmentières.
New food ideologies
The facility of the international exchanges of goods and the multiplied by ten possibilities of conservation or artificial ripening practically made disappear, in the field of food, the scarcity. The pineapple, for example, formerly article of great luxury - at the end of last century, when the workman gained 25 centimes of the hour, the fruit cost 25 gold francs -, sest from now on usually consumed: between 1977 and 1987, in France, the pineapple consumption was multiplied by eighty.
The desire of social distinction thus passes hardly any more by the adoption of rare and expensive foods. On the other hand, from new signs came to invest food from now on offered in infinite variety to the choice of the consumers. Carried, after 1968, by the vagueness of the “return to nature” and the natural products, the brown bread and the farmhouse bread dethroned, in the average and higher layers of the company, the rod of white bread, which however symbolized during centuries refinement and opulence. White sugar knows a similar evolution. Fustigated by the dietetic regulations, the sugar consumption singularly decreased in the last quarter of the XX E century. To start again it, the sugar industries “reinvented” of the products, known for a long time but abandoned in consequence of improvement of the standard of living: sugar is thus become again of the “true” little refined cane sugar.
By the means of the media and publicity, other ideas were essential in the public, in particular the concern of the “line” and the “form”. In Occident, animal greases - which would dangerously increase the cholesterol level of a population become too sedentary -, oils, the starchy foods and sugar, all things which has the reputation to make grow bigger, are avoided more and more. The animals for slaughter must imperatively be “thin”: one cannot appreciate any more the hazel nut taste of the ham fat. Much more, one less and less eats beef in France where its sale dropped by 2.3 % in 1987, of 3.8 % in 1988 and 5.2 % in 1989. At the end of the years 1990, the French do not consume any more, on average, that 18 kg per annum, that is to say a steak of 150 G every three days. Unlike times spent, this fall of consumption of the “red” meat, which is the fact of the easiest social categories, is a sign of prosperity. The roast or the leg of the middle-class tables disappeared with the profit from chicken. The very fatty butter and cheeses are also scorned. All a series of “reduced” food knows the favor of the public today, and the margarine, lubricates vegetable origin, competes with butter. Other product whose consumption does not cease decreasing in France: bread. If, in 1850, the French ate on average 800 G of bread daily, they do not consume of them already more but 320 G in 1950, and only 180 G in 1990. The lenses, split peas and noodles are forsaken, victims at the same time of their nature of starchy foods and their image of proletarian food.
Tastes and colors
Certain reactions to the taste of food are innate. The newborn reacts by mimicry of repulsion for the bitter taste, of pleasure for the sweetened taste. In many languages, moreover, the word which indicates sweetened savor is also used to express the pleasure or of morals qualities. But, essentially, the food tastes are acquired during a training where the mother plays a determining role. They thus diverge much according to the individuals and the cultures. Thus the hot red pepper, which causes a feeling of burn due to the capsine, is appreciated in many countries, but not in Northern Europe. This last area knows many other resistances as regards taste: in 1878, the senator de Fonvielle proposes without success, within the framework of a parliamentary debate on the eradication of vermin, a receipt of soup to the cockchafers; in 1885, does the Holt English publish a work entitled Pourquoi not to eat insects? with a comparable failure. Nutritional qualities of the flesh of the insects are however undeniable. Hundred grams of African termites contain 610 kcal, 38 G of proteins and 46 G of lipids, whereas the same hamburger weight conceals only 245 kcal, 21 G of proteins and 17 G of lipids. But what is biologically edible is not always culturally edible. One consumes dog in Korea, in China. One refuses to eat horse in Great Britain or North America. The French divide with Asian unquestionable taste for frogs, but not with other Europeans nor with the Americans of North. In the Far East, one cannot support the strong cheeses whose the Westerners délectent themselves; on the other hand, one appreciates the fruit of the dourian there, with the fecal odor, which causes the nausea of the precedents.
Towards the universalization of the food?
All the year push tomatos, strawberries and melons d.ns the heated greenhouses of Iceland, Sweden or Belgium. All the year, of hens raised out of battery large eggs from 60 to 65 G lay. “No more season ago” to consume the products. The time of foods, in the developed countries all at least, is standardized.
The contact between civilizations causes changes with double direction in the dietary habits. If Europeans adopt many exotic products, one notes that the immigrant Africans in Europe generally replace the mashed potatoes of yam by potato starch, the sheets of manioc or baobab tree by lettuce, those of amaranth by spinaches in branch. Will the food of the men finish, it also, by being standardized from one end to another of planet?
Needs for the modern man The man, like any living being, must have a balanced food likely to bring the energy resources and plastics to him which it needs. Is the basic nutritional contribution estimated at approximately 2? 400 kcal/j for a sedentary individual, but it varies with the sex, the age and the activity. It corresponds to the energy losses and plastics that the organization undergoes during twenty-four hours. The food must cover this expenditure by respecting the proportions of the glucidic components (from 50 to 60 %), lipidic (from 30 to 35 %), proteinic (from 10 to 15 %) and essential minerals.
The World Health Organization defined a minimal proteinic contribution of safety are equivalent to 25 g/j, but the contribution being of unequal quality, it is necessary to envisage from 70 to 80 g/j, also divided between animal and vegetable proteins, to obtain various amino-acids. For glucids, the contribution must reach 350 g/j, of which 10 % only are provided by sweetened food. The lipidic contribution, about 90 G, must be of quality, because it gets for the organization certain fatty-acids that this last is unable to synthesize.
To define the needs for the organization out of rock salt and vitamins, one determines the average minimal amount as a preliminary allowing to avoid the signs of deficiency. It is then multiplied by two factors, one fascinating of account the variation of sensitivity between the individuals and the other ensuring a comfortable safety margin. The quantities (about the milligram) thus defined are higher than those naturally necessary to the organization, but remain deprived of toxicity. In the same way, water is vital for the human organism, of which it composes two thirds, and ensures the transport of rock salt and the products of excretion. The daily requirements out of water for an adult are estimated at 2 L and must be covered by drinks and solid foods.
These estimates are worth only for one young, in good health and alive man under a moderate climate. It is thus often difficult to apply them to populations from which the living conditions and the dietary habits differ too radically. They should be used as indicators of an order of magnitude.
Metabolism and activity
The basal metabolism corresponds to the minimal energy expense to maintain a body at rest. It has been the energy consumption of an individual with jeun for at least twelve hours, whose muscular rest, the calm emotional one and thermal neutrality (18 °C) avoid the additional expenditure. This measurement is expressed in calories, unit traditional in physiology, or consumed liters of oxygen per hour and body unit of area. The basal metabolism corresponds to an average loss of 40 kcal/h/m ² for a 20 year old man, and a little less for one woman. From 25-30 years, it decreases regularly with the age.
Generally, basal metabolism, or metabolic activity, is measured by a technique of indirect calorimetry respiratory; the measuring unit is expressed in liter of consumed oxygen. Indeed, the oxygen uptake provides a relatively reliable estimate of the intensity of the metabolism. One liter of oxygen makes it possible to extract on average 4.85 kcal from food. The spirometers are the apparatuses making it possible to know instantaneously the volume of oxygen consumed by an individual, and thus the level of its metabolism.
The energy contribution must take into account the related spending with the activity of day before: is it at least of 800 kcal out of the 2? 400 kcal, but its value depends on the work carried out by the individual (of the activity of office to the sports activity). In addition, the energy of the nutrients not being completely reconverted in mechanical energy, the output of the effort is not total. There exist in particular losses of heat. Thus, work required is six times higher than effective work. Even at a well trained subject, the physiological output of work can hardly exceed 25 %.
The animals at constant temperature (homéothermes), the man forms part, devote a fraction of the additional energy expenditure to their thermoregulation. To maintain a temperature body stable, particularly if the environment is at a lower temperature, the organization “burns” more nutrients to produce heat. The man, whose capacities of thermoregulation are largely lower than those of the species living in cold zones, lives more easily in moderate country.
The emotions, their physiological and behavioral consequences, are also likely to modify the energy expenditure of an individual. The feeling of fear is often generating of “cold sweat”. During an examination, it is advised to provide itself with an energy in-case to compensate for the losses of heat caused by the concentration: the chocolate, which provides 500 kcal for 100 G consumed, is most effective.
Specific needs
The nutritional needs are very dependant on the age and the physiological state of the individual.
In an expectant mother, the growth of the fetus orders an increase in the food supplies naturally. The energy needs increase during the second and by the third quarters of the pregnancy to reach 350 kcal. This increase relates to all the nutrients, especially the iron, whose deficiency is announced at 30 % of the expectant mothers in the developed countries, and 60 % in the countries in the process of development. In the case of twin pregnancies, a particularly rich food is recommended. The food needs are further increased during breast feeding, the additional ration being estimated at 550 kcal/j.
The daily needs for the infant are of more than 110 kcal/kg during the first year, period of growth important. The requirements out of proteins and essential amino-acids, directly related to the increase in the body mass, are proportionally more important than those of an adult. Moreover, the new-born babies, whose system of thermoregulation does not function yet perfectly, know sometimes considerable energy expenditure. By its richness, the mother's milk allows a normal development of the child up to 6 months. Lastly, the hydrous needs for the baby are rather raised, up to 120 ml/kg/j.
The needs for the children are very different from one individual to another, of 1400 to 2200 kcal up to 9 years. But, generally, the growth like the multiple play activities or sporting require a food adapted to this energy expenditure. The needs, calculated proportionally with the weight, are in general more important than at all the other stages of the life. Do they pass to 2? 600 kcal for the boys from 10 to 12 years and to 2? 400 for the girls of the same age. The food must be varied and enriched in vitamin D in the countries slightly sunny.
The growth of the teenagers is less considerable than that of the children, which resounds on their food needs: the boys, who generally “are spent” more, ask for 2900 kcal. But this period of the life can be marked by problems of a psychological nature to the fatal consequences on food (bulimia, anorexia, etc).
The malnutrition of the elderly is often a real problem, even in the companies known as “advanced”. Indeed, at this stage of the life, several factors contribute to decrease the food intake day laborer: difficulties of chewing related to the loss of teeth limit the consumption of certain food as the meat. More generally, the major reduction in the incomes has consequences on the quality and the quantity of bought food. Living often alone, the elderly are hardly incited to take regular and balanced meals.
Classification of food
The food is divided into five or six groups, according to their nutritional value or their chemical composition, their character aperitif and their economic and cultural value.
The first group
The first group understands rich foods in proteins such as the dry meat, fish, eggs and vegetables. The meat counts on average 20 % of proteins rich in essential amino-acids. Its content of lipids is very variable. The lean meats (horse, game) contain some less than 5 %, while the fatty meats (pig, hear) can contain some from 20 to 30 %. On the other hand, the glucids are practically absent from this food, where it is not practically found that vitamins of the group B. the egg is very rich in iron and in vitamin A. the fish contain less lipids (between 1 and 20 %), but their rate of beneficial polyunsaturated fatty-acids is higher. The vitamins has and C are concentrated in the liver, while the vitamin D is distributed in the flesh. The shellfish have a close composition, with a lower content of lipids. The dry vegetables contain very little water and lipids, whereas their content glucids is important.
The second group
The food of the second group understands milk and the dairy products. They are rich in proteins, in vitamins (has, B and D), out of calcium, and the lactose is the independent source of glucids. They are almost complete food, only overdrawn out of iron and vitamin C. Their proportion in lipids varies between 80 % for butter and 99.9 % for plant oils. The protein average rate in milk is of 3.5 % compared with 2 to 8 % for the lipids, according to the animal origin. The yoghourts or the cheeses (fresh, fermented or cooked) are manufactured starting from milk, but during the preparation part of the vitamins and rock salt are lost. Their content of lipids is extremely variable (of 0 with more than 75 % of the matter dries) and depends as much on the manufactoring process as of milk used.
The third group
The third group understands greases, heating sources the most condensed. They improve the consistency of food and saturate the appetite long enough. Good market, butter except, they pose problems of digestibility; this is why they belong to the current medical concerns, in particular for the people suffering from a too high cholesterol level. Oils and the vegetable fats and animal are practically deprived of glucids or proteins (approximately 1 %), and rock salt are there often only with the state of traces.
The fourth group
In the fourth group, one finds rich foods in glucids: cereals and their derivatives (bread, cookies, flour, pasta products, etc). The glucids are presented primarily in the form of starch (from 65 to 70 %) and very little in free form. The cereals contain relatively little water (14 % to the maximum). The cereal proteins (from 6 to 12 %) are not excellent biological value, because they always do not contain the whole of the essential amino-acids. The lipids, contained in the germ, are in small quantity (3 %). Lastly, the major part of rock salt is made up of calcium, potassium, phosphates and magnesium, but the presence of phytic acid in the cuticle of certain cereals blocks the absorption of calcium and iron.
The fifth and sixth groups
One in general gathers food of the fifth and sixth groups, which understand the fruits and vegetables believed and cooked. This food, of very diverse botanical origins, has jointly to be very rich in water, rock salt and vitamins (especially in vitamin C). The lipids are generally slightly represented, except in the oleaginous fruits (nut and almonds), and proteins, although of good biological value, are represented only to 1 or 2 %.
Physiology of the need
A center of the hunger and a center of satiety, localized in the brain, intervene on the hypothalamus after having detected the metabolic signals (glycemia or insulin) of one of these two states, but also the sensory signals (olfactive, gustatory) and mechanics (slack stomach). The center of satiety stops the food catch by inhibiting the action of the center of the hunger which had started it. These centers are of permanent connection and undergo sometimes the risks of the emotional sensory component, which can start a followed excessive food catch by symptoms of obesity.
Food in the world The economic factors and cultural, very variable of an area with another and a fortiori of a continent with another, are at the origin of a large variety in the modes of food consumption.
Food and climate
The temperature and altitude are the two essential climatic factors which have repercussions on the food needs. The room temperature influences the quality of food to be consumed, but also their quantity. When the temperature drops, the metabolism of the individual increases. An investigation made it possible to estimate that to a fall of 10 °C of the temperature corresponded an increase in the heating needs for 5 %. Moreover, the wearing of heavy clothing, the difficulties of displacement caused by the bad atmospheric conditions (wind, snowing up) increase the heating expenditure. The basal metabolism of the Lapps is thus from 15 to 20 % higher than that of the inhabitants of the moderated areas, even when those take part in a forwarding in cold zone. Do the specialists in polar forwardings advise a ration day laborer of 3? 500 to 4? 500 kcal, very rich in lipids. Perspiration, the diuresis increased because of the cold and the great quantities of steam dissipated with the expiry strongly increase the requirements out of water.
In the countries with tropical climate, where the temperature is raised, one observes on the contrary a fall of the appetite and food intake. The basal metabolism is also decreased by 5 to 10 %. The salt and water losses by perspiration are particularly important, and these elements must be quickly replaced.
Does altitude cause a modification of the food needs only beyond 3? 000 Mr. This change is related to three factors: the rarefaction of oxygen, fall in the temperature and physical effort imposed by the broken nature of the grounds. Because of the fall of oxygen content of the atmosphere, the food must be rich in glucids, nutrients of which heating profitability is largest. The hydrous losses, also important in altitude, are due to the increase in ventilation and the very small relative humidity of the air. Part of the symptoms of the evil of the mountains is consecutive with this dehydration.
Classification by heating structures
The modes of food can be classified according to their heating structure. Eight groups of food are then defined: cereals, roots and tubers; fruits and vegetables; sugars and honey; dry vegetables; the fish and seafood; meat and eggs; milk and dairy products; fat contents and oilseeds. They are then divided into eight fundamental models of consumption: Anglo-Saxon, European continental, Scandinavian, Japanese, Mediterranean, Eastern-European, Uruguyan and traditional. If this classification highlights a similarity of food mode between country geographically or culturally close relations, it also underlines analogies between countries located at the antipodes from/to each other.
Another classification, making the share of the energy contributions of vegetable or animal origin, can, for example, being considered. Two great groups of country are then observed: one joins together Europe and North America, where the animal products bring from 30 to 35 % of the consumed calories; the other gathers the countries of Africa and Asia, South America, where this same food brings only from 7 à15 % of the consumed calories. This distinction corresponds to that existing between rich countries and poor countries. Meat consumption of the industrialized countries is of ten to twenty times higher than that of the countries in the process of development.
In the food model of the poor countries, only one basic food, generally rich in complex sugars, provides the main part of the energy contributions (from 60 to 90 %). The proteinic contributions are weak and primarily of vegetable origin. One thus observes proteoenergetic malnutritions associated with mineral and vitamin deficiencies.
Artificial recharge
The incidences of a hospitalization (increase in the basal metabolism, loss of appetite, digestive disorders or loss of conscience) can involve the malnutrition of the patient. It is thus sometimes necessary, even essential, to establish a nutritional assistance by digestive tract (entérale) or intravenous (parenteral). In the first case, a probe, passing by the nose, goes down to the stomach. The semi-fluid food, liquids or, are injected in a slow and continuous way by an electric pump. This method is used in the event of unconsciousness of the patient, serious ignition or obstruction (tumor, contracting) of its higher digestive tracts. The food by parenteral way, carried out thanks to a large catheter (hollow stem being used to dilate a blood-vessel), is exceptional. From short duration, it is used to put back the digestive tract, to treat a denutrition, etc
Food new technologies
Among the novel methods of agroalimentary, the treatment by ionizing rays makes it possible to destroy the pathogenic germs without deteriorating organoleptic qualities of food. In freeze-drying, the food products are quickly dehydrated vacuum, at low temperature (of -50oC with -60oC), and can be consumed after rehydration.
Used to improve appearance, savor, consistency or conservation of food, the additives are of natural or artificial origin. Chemicals can be used in France only if it is the subject of an interministerial decree, after opinion of the Superior council of the public health and the national Academy of medicine, in connection with the Scientific committee of the human consumption in the European plan (decree of February 12th, 1973). In Europe, 827 additives (of E 100 to E 927) are authorized - nearly 3000 in the United States - and approximately 200 additives or treatments after harvest were it in France in 1990, other than the physical treatments. Their membership, their name or their symbol IT must be indicated on prepackaged food.
A many food contains additives, and the legislation, different in each country, authorizes the use of these substances after tests of harmlessness on the animal.