Metabolism defines all of the linked reactions which occur in body cells. It involves two opposing mechanisms:
- catabolism: this enables energy to be extracted from foods by degrading energy- providing molecules (carbohydrates, lipids etc.) ;
- anabolism: this enables the synthesis of the constituents required for the structure and correct functioning of cells.
Basal metabolism is also distinguished from active metabolism.
Basal metabolism is the set of reactions which keep the body alive and therefore cannot be further reduced. It provides for respiration, heart beats, the feeding of the brain, body temperature, digestion etc.
Basal metabolism depends on many factors:
- age ;
It is generally around 1,200 to 2,000 kilocalories per day, which must be obtained from the diet. Excess consumption of kilocalories is then stored or must be removed by physical activity. Basal metabolism changes in nutritional deficiency (such as an excessively severe diet). It learns to consume less and store more, hence the greater weight gain which occurs at the end of a diet.
Active metabolism is the increase in energy requirements to enable the correct function of the body duringphysical exercise. Additional energy is consumed by active muscles although the amount of energy depends on the level of activity.
Active metabolism is far higher than basal metabolism. © KJohansson/Licence Creative Commons