Diet-induced thermogenesis means the energy that the body spends more each time food is taken. This is also why overweight people are often advised to split their daily calorie intake into many small meals.
Energy expenditure related to food thermogenesis corresponds, on average, to 10% of daily caloric consumption. It is given by two components: mandatory thermogenesis and optional thermogenesis.
Part of the energy expended is destined to the physiological and metabolic processes linked to digestion,
Part of the energy is spent as a result of sympathetic nerve activation, induced, for example, by nervine substances (Optional thermogenesis)
The thermogenic effect of food varies according to the nutrients that make it up:
Protids: they have by far the highest thermogenic value; the energy expended for the various processes described above amounts to 30% of the caloric intake provided by the proteins taken with food
Glucides: low thermogenic power (7% of the energy supplied)
Lipids: very low thermogenic power (3% of the energy supplied)
The thermogenic effect of proteins is higher than that of other nutrients, since the deamination of amino acids and the subsequent production of urea, costs a lot of energy to the body.
Even nervine substances, such as caffeine and related molecules (contained in tea, cocoa, guarana, etc.), have a fairly good thermogenic power.
Physical activity is the most variable item of energy expenditure, since it depends on the work habits and lifestyle of the subject.
In general, in a sedentary individual, the energy expenditure related to physical activity corresponds on average to 30% of the daily calorie expenditure.
It should however be kept in mind that the energy consumption related to physical activity is closely related to the subject's body mass. The more this is the greater and the higher the caloric expenditure associated with physical effort. This is obviously due to the greater energy demand required to move the high body mass; moreover, it must be remembered that the adipose tissue acts as a thermal insulator, preventing the dispersion of the heat produced. Overweight people are therefore forced to spend more energy to eliminate the heat developed during physical activity.
Humans are homeotherms, that is, they must maintain their internal temperature within a fairly constant range of values. All this costs the body a lot of energy, necessary for:
maintain internal homeothermies despite fluctuations in the external temperature
eliminate internal heat produced by metabolism and muscle activity