Human Nutrition

Human Nutrition. Nutrition is the science that studies the relationship between food and health, especially in determining a diet.

It is the process by which the food eaten by living beings is digested, absorbed and the products of its degradation are stored in the tissues and organs of the body , or circulate through the blood to fulfill different essential functions for life .

The correct diet, or better, the healthy diet, will be different according to age, nutritional needs, physical activity or specific periods such as those of rapid growth or pregnancy . For any age, the diet must be varied, balanced, pleasant and hygienically prepared. Varied when foods of the different basic groups are present: cereals and viands , fruits , vegetables , beans, meats , fish , eggs , dairy products, fats , sugars and sweets; and balanced because it includes the necessary quantities and proportions, distributed throughout the day.


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  • 1 Background
  • 2 Object of study
  • 3 Nutrients
    • 1 Macronutrients and micronutrients
  • 4 Bioavailability of nutrients
    • 1 Definition
    • 2 Influence of factors
  • 5 Dietary recommendations
  • 6 Nutritional requirements
  • 7 Recommendations for ingestion
  • 8 Sources


The essentiality of specific food constituents for human health and survival was discovered during the 19th and mid- 20th centuries . Previously, through trial and error observations, the safe sources of nutrients present in the vast amount of products available in nature were identified .

The nutrition of the superior animals had the bases of its knowledge in the consideration of three main components:

  • carbohydrates;
  • fats;
  • proteins.

The contribution of various sciences to nutritional studies has led to a breakthrough in knowledge regarding the role of nutrients in metabolism , nutrient deficiency and excess diseases , and their requirements.

The alarming increase in so-called chronic non-communicable diseases, in which nutrition and eating habits play an important role, has also been a stimulus to the dissemination of knowledge to broad sectors of the population .

The specialty of nutrition for athletes and for individuals subjected to intense physical exertion has also made progress from the diets that Greek athletes will have ingested in the year 776 ANE to current dietary planning.

Study object

Nutritional pyramid.

Nutrition is the process by which the food eaten by living beings is digested , absorbed and the products of its degradation are stored in the tissues and organs of the body, or circulate in the blood to fulfill different essential functions for life.

Nutrition, as a branch of biological sciences , studies the individual in relation to the food they eat, both healthy men and women , as well as those who have deviated from the normal pattern due to insufficient or excessive intake of nutrients.

The study of nutrition is the design of methods and strategies that allow early detection of malnutrition situations, by default or excess, and the ways for the recovery of malnourished individuals. It studies the possibility of influencing the prevention and treatment of diseases susceptible to dietary management, although its origin is not inadequate nutrition.

Nutrition is also aimed at studying the quality of food, its chemical composition , the bioavailability of the nutrients that make it up, and determining the requirements of each nutrient to propose dietary recommendations.

Advances in genetics and molecular biology have also allowed the study of the interactions between genes and nutrients to be incorporated into this science . On the one hand, the study of the influence of nutrients on gene expression, and on the other, the influence of genetic variations on the body’s response to nutrients.

Although nutrition has a body of knowledge that identifies it, scientific development has conditioned it to be closely related to other biological, physical , mathematical and social sciences .


Food is made up of a wide variety of compounds with different chemical structures, however, not all of these components have been classified as nutrients.

What elements determine that a chemical entity is classified as a nutrient?

A nutrient is a constituent of the diet, sufficiently characterized, natural or designed; It functions as a substrate that provides energy , a precursor in the synthesis of macromolecules, or other components that are required for cell differentiation , growth, replacement, repair, defense or maintenance, a signaling molecule , cofactor or a determinant of the structure, or normal molecular function and promoter of the cellular integrity of an organ.

Nutrients have been classified according to the amount in which they are found in food, and the amounts in which they are required by the body, in macronutrients and micronutrients.

Macronutrients and micronutrients

Macronutrients are those nutrients that supply most of the body’s metabolic energy. The main ones are carbohydrates , proteins , and lipids . Others include alcohol and organic acids. They differ from micronutrients like vitamins and minerals in that they are needed in small amounts to maintain health, but not to produce energy.

Macronutrients are made up of low molecular weight structures, some of which are essential for life. The essentiality of these simpler constituents ( amino acids in the case of proteins, fatty acids in that of lipids, and monosaccharides in that of carbohydrates ), lies in their impossibility of synthesis by the organism or in the importance of their function.

In addition to nutrients, food contains other non-nutrient compounds, some of which may be of importance to health. Nutrients are required in amounts determined by the body; if for long periods of time this requirement is not covered, symptoms of deficiency of that nutrient or of several that may be related to metabolism will manifest. In some cases, excessive intake of a particular nutrient can also lead to health disorders.

Nutrient bioavailability

It is said that in nutrition “not always the whole, is equal to the sum of its parts” ; This statement is based on the fact that, on the one hand, not everything that is ingested is used optimally, and on the other, the components of the food interact with each other, and can enhance or decrease the expected effect.


The bioavailability of a nutrient is defined as the amount of it, which reaches its target or target cell. It is generally accepted that it is the quantity or fraction of the administered quantity that reaches the circulation, and that it is not metabolized, complexed or excreted before exerting its biological effect . This definition is applicable to nutrients, drugs or other substances with biological activity.

For nutrients in particular, which are usually metabolized and the route of administration is through the diet, the notion of bioavailability is simply defined as the amount or fraction of the ingested dose that is absorbed. Actually the definition must include, in addition to absorbed, used, but the reason for the simplification is that the use of nutrients is a function of the nutritional situation and physiological state of the individual.

Influence of factors

There are many factors that influence bioavailability, such as:

  • nutrient interactions;
  • protein-protein interactions;
  • competition by structural analogy;
  • destruction of the compound by enzymes.

Dietary recommendations

Dietary recommendations are the conceptual basis on which the design of diets for the different age groups and physical activity conditions in normal individuals is supported. The most recent recommendations have been prepared by the Food and Nutrition Borrad of the United States and the FAO / WHO / UN Energy and Protein Expert Committees .

Nutritional requirements

Concepts of human nutrient needs have undergone variations at expert meetings on the subject, held by FAO and WHO since 1962 .

The requirement of a nutrient is defined as the quantity necessary for the maintenance of the bodily functions of the human organism, directed towards optimal health and performance.

The nutritional requirements of the human being have 3 components:

  1. the basal requirement;
  2. the additional requirement for growth, pregnancy, lactationor physical activity;
  3. adding safety to consider nutrient losses from handling and processing.

The nutrient requirement of the human being is influenced by the essentiality and function of the nutrient, by individual differences, environmental factors and by adaptation to the variable food supply. The absence of specific deficiency manifestations at certain levels of ingestion has been the structural basis on which a large part of the establishment of human nutrient requirements has been based. Additionally, the values ​​of the normal concentration of different nutrients in the body, their estimated daily losses and the calculation of a relative reserve capacity have been measured, established or reported for human beings with an acceptable state of health and good nutrition. These values ​​have been used as a basis for establishing intake recommendations.

Ingestion recommendations

Nutritional recommendation is understood as the quantity of a specific nutrient, capable of facilitating a normal functioning of the human metabolism, which is for practical purposes and has a purely population-based approach.

  • Recommended Dietary Supply (RDA):is the average daily dietary intake of a nutrient sufficient to supply the requirements of 97.5% of healthy individuals in a particular age and sex group of the population.
  • Adequateintake (AI): is the average daily dietary intake based on observed or experimentally determined approximations or estimates of the level of nutrient intake in apparently healthy groups of people, which is assumed to be adequate and used when it cannot be determined the RDA.
  • Average Estimated Requirement (REP):is the average daily dietary intake level that is estimated to be able to maintain the requirements of half of healthy individuals of a certain age and sex group.
  • Safe and Adequate Intake Levels (NSA):This term had previously been established when the existing evidence was sufficient to establish a range of requirements, but insufficient to structure its own recommendation. This category, together with the observation of maintaining the maximum level for the trace elements in the appropriate safety range, has been maintained in the recommendations since 1985 . Since vitamin K and selenium have already advanced from this level to established recommendations, they were moved to the main table of nutritional recommendations.

The establishment of NSAs for sodium , potassium and chlorine has been considered difficult to justify and only “minimum desired requirements” were estimated for these electrolytes. Sodium from 120 in the first 6 months of life to 500 mg / day in the adult, Potassium from 500 to 2000 mg / day for the same groups, and it was considered that 3500 mg / day of potassium could reduce the prevalence of hypertension and conditions cardiac.

  • Estimated energy requirement (REE):in the particular case of energy, the Defined Estimated Energy Requirement is established, as the average daily dietary intake level predicted to be capable of maintaining the energy balance of a healthy adult of a certain age, sex, weight, height and level of physical activity, which, in turn, is consistent with good health. In children, pregnant and lactating women, the REE is established to include the needs associated with tissue deposition and breast milk secretion at a rate consistent with good health.
  • Maximum Tolerable Intake Levels (TI): Themaximum average daily dietary intake level that is proposed without risks or adverse health effects for almost all individuals in a population. When ingestion exceeds this limit, health risks increase.


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