Nutrition (Latin nutrire: food) refers to the processes by which a living thing transforms food to ensure its operation. Nutrition is also a multidisciplinary science, with two main thrusts. Physiology of Nutrition deals with how the organization operates food processing, that is to say metabolic processes. This includes the study of the role of macro-and micronutrients in cellular biochemical mechanisms, and consequences on the tissue of an imbalance between energy absorbed and the energy expended by the body. The psychology of nutrition analysis feeding behavior of the individual or group. It focuses on issues such as "Why do we eat? Or "How do we choose our food? . In humans, these issues are related to environmental factors such as the built environment, media and health policies, as well as its characteristics such as income or culture.

Definition of food
Nutrition concerned with the relationship between living organisms and foods, it is necessary to define what is included as food. There are two definitions, according to the physiological or psychological approach. In the first, the food includes everything that is nutritious, that is to say that "ingestion is necessary for survival, good health and growth of youth". The psychological approach is more restrictive, considering that "the substance most nutritious food can hardly count as if nobody eats it [because] people do not usually think about what they eat in terms of nutrients. In other words, a food within the meaning of everyday life depends on cultural context: for example, whale eyes are nutritious because they contain protein and vitamin A , but an individual may not consider this an acceptable food.

There are many different nutrients, divided into two categories: macronutrients and micronutrients.

The organization draws its energy from sugars (or carbohydrates), fats (or lipids) and proteins. These three energy nutrients form the class of macronutrients. The organization may also draw its energy from alcohol (or ethanol), but it is not necessarily a recommended diet, unlike the previous three nutrients. Energy is measured in joules or calories, which are respectively the symbols J and cal. The conversion is 1 kcal 4.186 kJ, or 1 kcal 0.289 kJ. Energy is supplied to the body by reacting with oxygen, that is to say, by oxidation, which generates 9.44 kcal per gram of fat, 5.6 kcal per mL of alcohol, and varies with the type of carbohydrate: 4.18 kcal per gram of starch, 3.94 kcal per gram of sucrose and 3.72 kcal per gram of glucose. The energy obtained by oxidation of a gram of protein is 5.6 kcal but that does not match what the body withdraws, which is 4.70 kcal for this particular case. All organs for extracting energy is the digestive system, which converts sugars into glucose (or galactose), protein amino acids and fats into fatty acids. Each of these transformations is divided into several functional blocks: for example, the transformation consists of glucose digestion, hormonal regulation (that is to say the hormones present in plasma), use and storage ( in the liver, adipose tissue and muscle).

Sugars (or carbohydrates)
Carbohydrates are found in foods such as rice (up to 79.95 g per 100 g of long grain white rice, uncooked) or bread. According to the British Nutrition Foundation, the three main sources are cereals and 45%, potatoes and salty snacks to beverages and 12% to 10%. Carbohydrates are divided into categories depending on the number of sugar units: monosaccharides (or dares) to a unit, disaccharides (such as sucrose or disaccharide) to two, and polysaccharides (or glycans) beyond. A similar classification is obtained by considering the degree of polymerization DP: DP monosaccharide for 1 to 2, for oligosaccharide DP 3-9 polysaccharide and beyond.

The site of absorption of carbohydrates depends mainly on the class but also other factors related to the subject or quantity. For example, monosaccharides such as lactose is normally absorbed in the small intestine, but if the subject has an intolerance to lactose (carbohydrate in milk) lactose then continue his run of the small intestine to the large intestine where it is fermented to produce volatile fatty acid, the gases from this process include bloating generate, and are used for diagnosis of lactose intolerance by testing the presence of hydrogen. About 75% of adults have lactose intolerance, for example in Asian populations, and other problems related to the absorption of sugars exist such as sucrase-isomaltase deficiency affects 10% of Inuit in Greenland.

Carbohydrates are necessary for the body, and the concentration in the blood (usually between 70 mg / dl and 100 mg / dL) should be maintained at a fairly high level because the brain depends entirely. According to the average required by the brain, a daily intake of 130 g is recommended for adults. In practice, this contribution is easily exceeded, with a median of 220 g to 330 g in men and 180 g to 230 g in women. One of the interests of the physiology of nutrition is to see how the body adapts depending on the amount of nutrients provided. In the case of carbohydrate, if the quantity is low then the body tries to save the drawing more energy from fat, otherwise, energy can be taken from carbohydrates, which are then transferred from the blood into cells by insulin, and excess can be converted by the liver through a process called de novo lipogenesis (DNL). The excess is stored as fat and not carbohydrates, an explanation for the change being that the energy density of fat is higher than that of sugars, thereby minimizing the weight gain to maintain the mobility of the body.

Fats (or lipids)
Most fats are not soluble in water, which distinguishes them from carbohydrates and proteins. The classification of lipids Bloor distinguishes four categories. Simple fats are fatty acids linked by an ester bond to alcohols. For example, the result of a triglyceride molecule of glycerol esterified to three fatty acid molecules, and it is in the vegetable oil and animal fats. The fatty complexes have the same composition but with additional molecules: by esterifying glycerol with two fatty acid molecules and a phosphate complex is obtained phosphoacylglycerol. The derivatives are obtained by hydrolysis of the previous two, and what does not fit into any of the three categories is another (such as squalene). The structure of fatty acids is also classified according to the length of their carbon chain (short, medium, long, long) and the presence of at least one carbon-carbon double bond (unsaturated acid was then and this class contains the trans fatty acid).

It is considered acceptable that 20-35% of energy comes from fat. The role of all fatty acids is not yet well understood, and it is not possible to determine appropriate levels for their consumption in general. However, levels are considered adequate (which is not a recommendation) for certain essential fatty acids: the α-linolenic acid, omega-3 group, it is 1.6 grams per day for young men and 1.1 g for young women, and γ-linolenic acid, omega-6 group, the amounts are respectively 17 g and 12 g per day. Unlike the previous group Omega-9 does not contain essential fatty acids, but more research is needed on the health benefits.

During digestion, fats are emulsified in the stomach. The emulsifier is bile produced by the liver and stored in the gallbladder. The emulsion then enters the small intestine where the lipids are degraded by a process called lipolysis, associated with other molecules in a lipoprotein to be transported in the blood. A lipoprotein is shown in the diagram cons: lipids are inside and the outside is formed of different types of apolipoprotein, Apo noted, and phospholipids.

There are five classes of lipoproteins, various functions. For example, high density lipoprotein HDL avoid noted that cholesterol accumulates in blood vessels leading to the liver for disposal, these lipoproteins are called good cholesterol, and those doing the opposite is the bad cholesterol, LDL noted. The concentration of LDL increases with the intake of saturated acids or trans fatty acid, which also increases the risk of cardiovascular disease. Remove these acids from the diet may require fundamental changes that could give place to deficiencies, but it is possible to reduce the quantity, eg in the Mediterranean diet.

Proteins of animal origin are the main source in North America and Western Europe. The animal includes both the meat that is produced by animals, such as eggs (13.62 g protein per 100 g of fried egg) or cheese (19.80 g protein in 100 g Camembert). Vegetarians do not consume meat, and vegans rejecting all animal products, their proteins must come from vegetables and grains, which are also the two main sources in Africa, Asia and Latin America.

A protein consists of amino acids linked by bonds petptiques. These amino acids are separated into two categories: essential, that is to say, those that the body can not synthesize and must be supplied by food or non-essential. What is essential depends on the organism: for example, arginine is necessary for the survival of a cat but not for man past the infant stage. These categories are further refined by considering the essential amino acids under certain conditions. Indeed, some amino acids can be synthesized but with limited capabilities in general and variants under the conditions of the subject: for example, the synthesis of proline is limited in burn patients.

Proteins are an essential component of the body and perform a large number of roles. For example, a hair consists of keratin, a protein and is involved with another protein, collagen, in the strength and elasticity of the skin. Problems related proteins may also be associated with diseases, such as glutamate is involved in the crises of epileptic seizures. An inadequate intake of protein may therefore have strong and diverse body. The recommended amount of protein is given empirically to 0.80 each day per kilogram of body weight. It is recommended that the diet does not exceed 35% protein.

The PDCA (protein digestibility corrected amino acid scoring pattern) summarizes the quantities of amino acid, but due to controversies and technical developments, the amounts recommended by FAO and WHO can differ greatly according to reports. In 1985, he was advised to take each day less than 10 mg / kg threonine, and almost 30 mg / kg in 1991 to about 15 mg / kg in 2001. Technical Report 935 FAO / WHO is compiling an inventory in 2007. The digestion of proteins takes place primarily in the small intestine and releases the amino acids that continue to other organs. In case of under-nutrition, certain amino acids can be converted to glucose by gluconeogenesis.

A vitamin is a compound necessary for the metabolism of an organism, in the sense that a "about being deprived develop deficiency diseases and signs of abnormal metabolism, and restore the missing components will prevent or cure diseases and make the normal metabolism [B 1]. The fact that a vitamin is a compound distinguishes eg minerals, and necessity means that it can not be synthesized. Organisms are capable of various syntheses, the name vitamin is on the organism. Thus, vitamin C can be synthesized by most animals from glucose, and is therefore regarded as a vitamin for the synthesis of this species can not as humans and other species of the taxon Haplorrhini, bats -mouse or guinea pigs [B 2]. The reason for this deficiency in humans comes from the inactivity of the gene for the enzyme L-gulonolactone oxidase, necessary for synthesis from glucose, on chromosome 8.

Vitamin C is found in vegetables and fruits such as kiwi fruit (105.4 mg per 100 g) or cantaloupe (36.7 mg per 100 g). Vegetables and fresh fruits and raw are the best source, since the vitamin C content decreases sharply with age or cutting, and cooking strongly in [B 1].

The sensation of thirst can be understood by studying the mechanisms of red blood cells. The interior of a red blood cell, called cytoplasm, is separated from the outside by a membrane that allows water to pass, and for this reason is called semi-permeable. There is pressure from within and outside the cell, according to the respective concentrations of solutes. If the concentration outside is lower than in the cell, then it begins to swell because of osmosis and can eventually explode because the membrane does not stretch. The exterior is to say, the plasma is then described as hypotonic. Conversely, it may be hypertonic and the cell then tries to restore the pressure by letting the water out. This second scenario arises when there is not enough water in the body, less water means a higher concentration of solutes outside the cell. This pressure is a highly sensitive mechanism to trigger feelings of hunger: an increase of 2 to 3% is enough to feel a strong need to drink as well in humans as monkeys or rats. This effect is verified by injecting a solution with a high salt concentration, and intensity of thirst is proportional to the pressure.

However, the body also has its regulatory mechanisms: the base of the brain responds by secreting antidiuretic hormone that acts on the kidneys to conserve water by filtering urine. This pressure increases when a person eats, and this action also affects the kidneys, which need more water to waste. So drink before or during a meal helps to balance. Moreover, another body's response to increased pressure is a dry mouth due to reduced saliva. However, it can be concluded that having a dry mouth is a body mechanism to ensure that the individual drink: a cons-simple example is that individuals with salivary gland failing drink appropriate amounts, and thus feeling they feel does not push them to drink.

Understanding of the osmotic pressure provides an overview of basic mechanisms, but many problems remain open, such as how an organization determines the amount of water to drink.

Nutrition is defined here as the science which examines the relationship between food and health: a study of food composition, properties, and their use by the body. These studies lead to the diet. It also takes into account as part of nutrition, eating behavior of individuals, especially during meals or when snacking.

However, from clinical observation of disease whose origin was a dietary deficiency (eg scurvy), nutrition for today also diseases such as cardiovascular problems and cancer (with the method Kousmine example), osteoporosis and hypertension (excessive salt in particular), type 2 diabetes, obesity, autoimmune diseases, Alzheimer's disease.

Nutrition plays a vital role in preventing many diseases. For example, more than 100,000 cancer cases could be prevented each year in France, by simply changing eating habits.

We must also remember that nutritional status is a prognostic factor in the evolution of cancers. An undernourished person is at greater risk of complications that a person receiving a power supply to the body's needs.

The complex processes which nutrients are - interactions between food, degradation, transformation of energy and release this energy, transport and use of chemicals for construction (anabolism = construction catabolism = waste disposal) and specialized tissues maintaining good overall health - are only partly understood. Significant nutritional choices, however, must be made to ensure the good health of individuals, such as very young children and the elderly, and whole populations suffering from malnutrition.

Adaptation of feeding practices to the satisfaction of physiological needs is dietetics.

See also Protein