Determination of the optimal calorie number requires determination of the daily energy expenditure. For basic metabolism, in normal course of basic life processes (including work of the respiratory system, blood circulation, maintaining a constant body temperature, tissue regeneration), body composition (the non-fat body content, fat level in the body and age) have the decisive influence. Muscles require constant delivery of nutrients necessary to work and, hence, the more muscle tissue, the greater the metabolic rate. Lower rate of metabolism is associated with higher levels of body fat and old age. 24-hour energy expenditure is significantly affected by physical activity – it can absorb 30-50% of the energy obtained from food. Some of the energy (about 10%) we lose also due to the processes related to digesting and absorbing food.
In the case of women, daily energy demand is on average 2000 kcal/day, in the case of men – 2500 kcal/day. These values apply to adults with low or moderate physical activity. When you weigh too much and you want to lose weight, you should reduce the calorific value of the diet by 20-30%, which in practice means usually 1500-2000 kcal/day. In turn, very active, regularly exercising people, depending on their body weight, time and intensity of the training need from 2500 kcal/day up to 8000 kcal/day.