Energy Expenditure
The total calories burned through basal metabolism, physical activity, and the thermic effect of food. Weight management depends on the balance between energy intake and expenditure. GLP-1 receptor agonists primarily reduce energy intake through appetite suppression rather than increasing expenditure.
Technical Context
Total daily energy expenditure (TDEE) = BMR (60-70%) + thermic effect of food (TEF, ~10% — energy cost of digesting, absorbing, and processing nutrients) + physical activity energy expenditure (PAEE, 20-30% — most variable component). GLP-1 RAs primarily reduce energy intake (appetite suppression) rather than increasing energy expenditure. Some evidence suggests GLP-1 RAs may slightly reduce PAEE (patients are less hungry, potentially less active) while having minimal direct effect on BMR beyond what is expected from weight loss. Triple agonists (GLP-1/GIP/glucagon receptor) are hypothesised to increase energy expenditure through the glucagon receptor component — glucagon stimulates hepatic thermogenesis, fatty acid oxidation, and potentially brown adipose tissue activation. This could provide a metabolic advantage over GLP-1-only approaches.