Nutritional status

Energy is necessary to maintain the different bodily functions (respiration, circulation, digestion and metabolism of nutrients,...); also to carry out the different physical activities. Food provides the substrate to obtain this energy, which is achieved in living beings through chemical reactions of oxidation of the nutrients present in food.

Although proteins can also provide energy, the main energy sources are usually considered to be carbohydrates and fats.

The energy needs of an individual are those that allow him to reach a height in correspondence with his genetic potential, a weight appropriate to his size, a body composition within normal parameters and a physical activity appropriate to his age.

It can also be said that this level of energy intake allows the individual to achieve a good state of health in the long term.

When the weight is normal and stable, it means that the individual is in energy balance, that is, a neutral balance between energy expenditure and energy intake. When this balance is usually positive, there is a tendency to obesity, and when it is negative, weight is lost but there is also a risk of malnutrition.

The relationship between energy intake and body weight is not linear, but parabolic. This is because body composition is modified according to intake and body weight variation. In other words, weight gain does not only mean accumulation of fat mass, but also of fat-free mass (muscle mass, bone, blood, etc.). This is the reason why overweight people usually have higher energy needs than people of the same size, age and sex, with a normal body weight.

When energy intake is reduced, weight loss is more noticeable initially, slowing down later due to loss of fat-free mass.

Basal energy expenditure (BEE)

This is the energy needed to maintain the metabolic processes of cells and tissues and to carry out different body functions. It is obtained by extrapolating to 24 hours the amount of energy consumed at rest and fasting (after 12 to 18 hours from intake) at a neutral temperature.

The main determinant of GEB is