Thermic Effect of Food (TEF)
The calories your body burns digesting what you eat
Plain English
Thermic Effect of Food is the energy cost of digesting, absorbing, and processing the food you eat. Every meal requires a calorie investment to break down and metabolize its nutrients, and that investment varies significantly depending on the macronutrient composition of the meal. TEF accounts for roughly 10 percent of total daily energy expenditure for most people on a mixed diet.
The Mechanism
Not all macronutrients cost the same to digest. Protein carries the highest TEF, requiring 20 to 30 percent of its calories just to be processed: a 100-calorie portion of protein yields only 70 to 80 net calories after the cost of digestion. Carbohydrates cost 5 to 10 percent to metabolize. Fat is the most efficient, costing only 0 to 3 percent, meaning nearly all of its calories pass through digestion with minimal energy lost as heat.
The mechanism behind protein's high TEF is primarily the energy cost of amino acid metabolism, urea synthesis, and gluconeogenesis. Protein breakdown and reconstitution into new tissue or fuel is metabolically expensive compared to the relatively straightforward oxidation of glucose or fat. This is one of the contributing mechanisms behind the body composition advantage of high-protein diets, separate from satiety and muscle-preserving effects.
TEF is measured as the heat generated during digestion, which is why it is sometimes called diet-induced thermogenesis. In practical terms, a person eating 2,500 calories per day can expect roughly 200 to 300 calories of that total to be expended just in the process of digestion, with the exact number shifting upward as protein intake rises and downward on high-fat, lower-protein diets.
Why It Matters
Your food choice changes how many calories actually reach your tissues.
TEF is the reason that a 200-calorie serving of chicken breast and a 200-calorie serving of olive oil do not contribute equally to your energy balance: after digestion, the protein has surrendered 40 to 60 calories in the process while the fat has surrendered almost none. This is not enough to override overall calorie intake, but it is a meaningful edge that compounds over time on a high-protein diet. For someone eating 180 grams of protein per day versus 80 grams, the TEF difference alone can represent an additional 100 to 150 calories of daily expenditure, equivalent to a 10 to 15 pound difference in body weight per year if all else is equal.
Common Misconception
A common misconception is that TEF is negligible or not worth considering. At 10 percent of total daily expenditure, TEF is roughly equivalent to most people's formal exercise contribution, and it is entirely passive: no gym session required. The error cuts the other way too: some people overcorrect and assume high protein intake dramatically raises metabolism. The TEF boost from protein is real, but it works in the background as a modest, persistent edge, not a dramatic calorie-burning mechanism to rely on independently.
How to Improve It
3 Things to Remember
TEF accounts for roughly 10 percent of total daily calorie expenditure on a mixed diet, making it roughly comparable in size to most people's formal exercise contribution, completely passively.
Protein has a thermic effect of 20 to 30 percent, meaning up to 30 calories per 100 calories of protein are burned just in digestion; fat costs 0 to 3 percent, making macronutrient composition a meaningful lever on net calorie intake.
High-protein diets provide a compounding TEF advantage: 180 grams of protein daily versus 80 grams can produce 100 to 150 additional calories of passive daily expenditure through digestion alone.
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