Fig. 1: Physiological regulation of energy metabolism.
From: On the pathogenesis of obesity: causal models and missing pieces of the puzzle
Humans eat food primarily to meet the body’s energy and nutrient needs for life-sustaining functions (basal metabolic rate, BMR) and all body movements (physical activity energy expenditure, PAEE) and, in some cases, thermoregulation. Food passes through the gut, and nutrients are absorbed into the systemic circulation, affecting secretion of gastrointestinal and pancreatic hormones (for example, insulin). Energy expenditure increases because of the thermic effect of food (TEF), and energy-yielding substrates are partitioned among tissues and intracellularly between oxidation and storage pathways, depending on their availability and demand, under the influence of many hormonal and neural signals. Energy can be stored in and mobilized from various organs and tissues. The brain can sense signals relaying information about energy and nutrient needs, body energy stores and circulating fuels and adjust food intake and peripheral metabolism accordingly by various efferent neural signals (for example, via the autonomic nervous system (ANS)) and by modulating the secretion of neurohormones. Physical activity and many other factors (genetic, behavioural, psychosocial and environmental) can modulate these pathways.
