Energy Requirement and Basal Metabolism

For further information: food energy released from the in vivo oxidation of macronutrients corresponds to approximately:

• 4.00 kcal for each gram of protein
• 3.75 / 4.00 kcal for each gram of carbohydrates
• 9.00 kcal for each gram of lipids.

While carbohydrates and lipids are completely demolished during oxidative catabolism, not all the energy contained in the amino acid molecules is released. In fact, the nitrogenous part of the amino acid, called the amino group, is previously removed and destined for a particular metabolic pathway (formation of ammonia , urea cycle and subsequent urinary elimination of nitrogenous waste). The remaining part of the amino acid, called the carbonaceous skeleton, is used to produce energy.

The energy coming from the catabolism of macronutrients is used by the body to support the energy demands deriving from:

• basal metabolic rate (60-75%)
• Diet-induced thermogenesis or TID (10-15%)
• physical activity (not necessarily sports (15-30%)
• thermoregulation and other causes.

Basal metabolic rate (BMR) is defined as the energy expended by the body to carry out normal vegetative functions and stay alive. These functions, vital because they cannot stop, include:

• breathing
• heart rate and blood circulation
• renal filtration
• hepatic activity
• brain activity
• glandular secretions
• the maintenance and renewal of body tissues.

and the height of the subject, returning the corresponding extension of the body surface.

At the same weight, a taller subject has a greater body surface area and, consequently, a higher basal metabolic rate than that of a shorter subject.

Basal metabolic rate is influenced by many factors:

sex by virtue of the greater muscle mass, the basal metabolic rate is higher in men than in women. Muscle tissue is in fact very metabolically active and, both during physical activity and during rest, it allows us to burn many calories. age the basal metabolic rate reaches its maximum values ​​in the first years of life; just think that a baby triples its weight within twelve months of birth; after 10 years, even if very gradually, the basal metabolic rate tends to decrease, decreasing more and more with the passing of the years nutrition a malnourished person has a lower than normal basal metabolic rate; this phenomenon is responsible for the failure of many slimming diets which, due to "excessive caloric deprivation, depress the metabolism of those who follow them fitness physically active people have a higher basal metabolic rate, since energy consumption remains high even after several hours from the end of physical exercise climate people living in warmer countries generally have a slower metabolism, presumably due to "lower thyroid activity body temperature when the body temperature rises all the chemical reactions of the organism undergo an acceleration; in particular, for each degree of temperature above the norm, the metabolism undergoes a "surge of 13% hormones thyroid hormones, testosterone, growth hormone and catecholamines have the ability to accelerate basal metabolism pregnancy especially during the last trimester of gestation, there is a greater energy expenditure to support the growth of the fetus; this also applies to nurses, who need more energy for milk production sleep

during peaceful sleep the metabolism is essentially lowered for two reasons: in similar conditions the sympathetic activity ceases and muscle tone decreases (even at rest, as long as awake, a small part of muscle fibers is contracted; this phenomenon takes its name muscle tone).

During sleep, however, all the fibers are completely relaxed and muscle tone is lost. For this reason, the basal metabolic rate should never be measured during sleep

some medications and supplements amphetamines, caffeine, ephedrine, guarana, thyroid hormones and the like, appreciably raise the basal metabolism

The measurement of the basal metabolic rate is useful in the sports field, but also in the medical one, for example in the evaluation of some metabolic diseases, such as thyroid dysfunction, obesity and diabetes.

For further information: Diet-induced thermogenesis