Energy spent digesting each macronutrient
The thermic effect of food (TEF) is the energy the body burns to digest, absorb, and process a meal. It differs sharply by macronutrient. Protein has the highest TEF, with commonly cited estimates of roughly 20 to 30 percent of its calories used in processing. Carbohydrate sits in the middle at about 5 to 10 percent, and fat is lowest at roughly 0 to 3 percent because it is stored with little metabolic conversion.
Part of protein's high cost comes from the energy needed to deaminate amino acids and synthesize new protein or urea. Alcohol also carries a notable thermic cost but is not a nutrient the body stores efficiently.
How much TEF moves the daily total
Across a mixed diet, TEF accounts for roughly 10 percent of total daily energy expenditure, so shifting macronutrients changes that slice modestly rather than dramatically. A higher-protein diet can raise the TEF component somewhat, which is one reason protein is associated with easier appetite control and weight maintenance, alongside its satiety effect.
These percentages are population averages from indirect-calorimetry studies and vary with meal size and individual metabolism. This is general nutrition information, not medical advice.