The thermic effect of food describes how much energy the body spends purely on digesting, transporting and processing a nutrient. This energy expenditure is, in effect, deducted from the calories consumed and differs markedly between nutrients. For carbohydrates the value is usually around 5 to 10 percent, and for fat it is lower still, which illustrates the differences between nutrients.
For protein, the thermic effect is the highest compared with carbohydrates and fat. In nutrition science, figures of around 20 to 30 percent of the energy consumed are often cited, while for carbohydrates and fat it is clearly less. In practical terms, this means that of 100 calories from protein, a larger share is used up in processing itself than with other nutrients. For the total energy balance of a day, the thermic effect plays a minor but measurable role alongside physical activity and basal metabolic rate.
The thermic effect is often considered together with the satiating effect of protein, and more on this can be found in the entry Satiety. Context on weight loss is provided by the guide Protein for weight loss.
