WHAT IS ENERGY BALANCE AND HOW IS BODY WEIGHT REGULATED?
Energy Balance
Energy Balance (EB) is defined as the result of the following equation:
EB= Energy intake – Energy expenditure
Energy intake is provided by means of nutrients in the diet: fats (9 Kcal/g), proteins (4 Kcal/g), carbohydrates (4 Kcal/g) and fiber (1.5 Kcal/g). Energy expenditure results from the addition of a) basal energy expenditure (BEE): consumption of energy while at rest, calculated according to sex, age and body weight. It represents 50 to 70% of the energy expenditure; b) energy expenditure while performing physical activity: calculated according to sex, age and level of physical activity (mild, moderate, intense or exceptional); and c) food-induced thermogenesis: consumption of energy produced against several stimuli such as the ingestion of foods, cold, stress, etc. It accounts for 10% of the total energy expenditure.
The basal energy expenditure is calculated using different valid formulas and determination of a correction per activity.
When the energy intake is greater than the energy expenditure, there is a positive or surplus energy balance and this excess causes fat deposits and increased body weight. However, when the energy expenditure exceeds the energy intake, there is a negative balance producing a decrease in fat deposits and thus decreased body weight. In normal situations, this balance fluctuates without any significant changes taking place in the fat deposits or body weight, as a number of mechanisms act to equate intake with expenditure. When the positive or surplus balance is maintained over a long period of time, obesity may result.
Regulation Of Food Intake And Appetite Control
Food behaviour is a very complex phenomenon in which external or environmental factors as well as other intrinsic factors of hormone, nervous or metabolic nature intervene.
Intrinsic factors include those that are under the control of the central nervous system and those that are under peripheral control (mainly gastrointestinal fat tissue).
a) Peripheral control mechanisms: Hunger and satiety are regulated by short-term control mechanisms (which regulate the duration and amount of foods) and other long-term control mechanisms (that regulate stores and energy balance).
Short-term satiety factors are explained by a large number of more or less complex metabolic theories. Some theories attempt to explain satiety as a function of the amount of protein ingested in the diet (aminostatic theory) or as a function of the use of glucose (glycostatic theory). Apart from these theories, it is well known that secretion of different gastrointestinal hormones (such as bombesin, glucagon, somatostatin, cholecystokinine, GIP, among others) at the time of digestion make it possible to reduce food intake.
The existence of signals that control food intake and body weight at long term is becoming of increasing importance, in part after the discovery of leptin.
Leptin is a protein synthesised in adipose tissue and is closely correlated with the contents of fat body mass. When fastening it decreases rapidly, making the individual feel hungry.
b) Central control mechanisms: The central nervous system plays a role in the control of food intake by means of at least three mechanisms: control of hunger and satiety, control of energy expenditure and secretion of hormones that regulate energy storage. Through several of its nuclei (arcuate nucleus and paraventricular nucleus), the hypothalamus acts direct and indirectly on food intake, appetite, and control of body temperature, and thus controls food intake, energy expenditure and body weight. A number of substances are capable of stimulating or inhibiting hypothalamic responses, influencing food intake and body weight. An important substance in this group is the neuropeptide Y (NPY) that stimulates appetite and decreases calorie expenditure.