Thermogenesis
The body's production of heat, notably during digestion (the thermic effect of food) and through brown fat, contributing to daily energy expenditure.
Thermogenesis is the production of metabolic heat. It contributes to total energy expenditure through several mechanisms:
- Thermic effect of food (TEF): the energy spent digesting, absorbing and metabolising what you eat
- Adaptive thermogenesis: heat production in response to cold or overeating
- Brown fat thermogenesis
An original angle (protein “costs” energy to digest): the thermic effect varies enormously between macronutrients:
- Protein: 20 to 30% of its calories are burned just digesting it!
- Carbohydrate: 5 to 10%
- Fat: 0 to 3%
In other words, out of 100 kcal of protein eaten, about 25 are spent on digestion, leaving only about 75 “usable”. This is one of the mechanisms that makes high-protein diets effective for weight loss (beyond satiety).
Brown fat, a fascinating angle: unlike white fat (storage), brown fat (brown adipose tissue) BURNS energy to produce heat, thanks to a protein (UCP1) that “uncouples” the mitochondria. Babies have a lot of it (to keep warm); adults keep pockets of it (neck, shoulders).
Cold exposure (cold showers, cool temperatures) activates and develops brown fat, increasing energy expenditure. This is a promising area of research, although the effects on weight loss remain modest in humans.