The traditional units of measurement of energy or caloric value of food are kilocalories (Kcal), popularly known as calories and represent the amount of heat needed to raise the temperature of a Kg of water by 1 ° C.
Energy can be obtained from carbohydrates, lipids, proteins, and alcohol, present in food and beverages for the maintenance of vital functions of the body.
The raw energy of a food depends on its energy nutrient content and can be determined from a calorimetric pump, which quantifies the heat produced by the combustion of nutrients in the presence of oxygen. Thus, for different carbohydrates, it ranges between 3.9-4.2 kcal / g, in proteins between 5.2-5.9 kcal/g and in lipids between 9.2-9.5 kcal / g, while Alcohol contributes between 7.1 kcal/gram.
The reactions of a transformation of energy from food, take place in different compartments of the body and are intended for the maintenance of bodily functions, different physical activities, the use and use of nutrients and an important part is dissipated in a way of heat
The total energy contained in food, in addition to being used in the production of ATP, necessary for different cellular functions, is also consumed in the processes of use of nutrients, such as digestion, absorption or assimilation by the body and in the replacement processes of components and body structures.
At rest, the body obtains energy primarily by oxidation of fats with a low consumption of carbohydrates; However, at the beginning of the exercise and during a prolonged exercise, the proportions of glucose, fatty acids and other energetic substances consumed can be modified depending on the duration, intensity, and type of activity, as well as the training and the previous diet followed.
In situations of fasting or caloric restriction, the organism depends on its own energy deposits. Thus in fasting periods of 12-18 hours, the body initially uses glucose and circulating fatty acids in the blood, as well as liver and muscle glycogen. Subsequently, if the fast is prolonged, the body obtains energy from the amino acids, which are used directly as energy substrates. Prolonged use of lipids as an energy source leads to the appearance of ketone bodies with a reduction in glucose utilization.
The vital functions of the organism require a certain energy expenditure, which must be compensated by food and beverages from the diet. Thus, energy needs are defined as the amount of energy needed to maintain health, growth and an appropriate level of physical activity.
In equilibrium situations, the adjustment between ingested energy and the daily energy consumption is achieved through different mechanisms, which regulate appetite and energy expenditure, avoiding large variations in weight over time and, therefore, the caloric malnutrition and obesity.
In certain circumstances a part of the energy contribution of the diet can also be used for the growth of body structures, milk production or the development of the fetus during pregnancy. However, mental activity hardly influences energy expenditure.
Components of energy expenditure
- The concept of basal metabolism encompasses that energy expenditure destined to the maintenance of vital functions such as cardiorespiratory activity, excretion, maintenance of body temperature, maintenance of muscle tone, etc.
- Physical activity: it is usually classified according to the cardiac or respiratory activity and through oxygen consumption. With these criteria, energy expenditure for different activity levels is estimated at:
- Sedentary activity: 2.5 kcal / min.
- Light activity: 2.5-5 kcal / min.
- Moderate activity: 5-7.5 kcal / min.
- Heavy activity: 7.5-10 kcal/min.
- Very heavy activity: more than 10 kcal/min.
- Thermogenic action of food: the energy consumption used in the digestion, absorption, distribution, excretion, and storage of nutrients is called. In a mixed diet, food-induced thermogenesis is not more than 10% of total energy expenditure, with proteins that carry most of the consumption.
Body composition depends on different factors such as age, sex, etc. It can be affected by physical exercise, which favors the deposition of proteins and the reduction of fatty deposits, as well as certain hormonal alterations.
The human organism is mainly formed by water (50-70%), proteins (12-20%), fat (10-30%), minerals (5-10%) and carbohydrates (1-2%).