The thermic effect of food (TEF) is the energy your body spends digesting, absorbing and storing what you eat. It is why expenditure rises for a few hours after a meal, and over a day it comes to roughly a tenth of what you ate. It is real, it differs by macronutrient, and it is already inside every TDEE estimate you have ever been given — which is the part most explainers leave out.
TEF defined
Researchers call it diet-induced thermogenesis; nutrition writers call it the thermic effect of food. Same thing. Westerterp's review defines daily energy expenditure as three components — basal metabolic rate, diet-induced thermogenesis and the energy cost of physical activity — and describes TEF as the increase in energy expenditure above basal metabolic rate after eating1. The FAO/WHO/UNU expert consultation calls it the metabolic response to food and puts a number on it: it increases total energy expenditure by about 10 percent of the BMR over a 24-hour period2.
Two ways of stating the size, then, and they agree closely:
| Source | Statement | On our 85 kg example (BMR 1,830; TDEE 2,837) |
|---|---|---|
| FAO/WHO/UNU 20042 | ≈ 10% of BMR over 24 h | ≈ 183 kcal/day |
| Westerterp 20041 | 5–15% of daily energy expenditure on a mixed diet at energy balance | ≈ 142–426 kcal/day |
| Textbook rule of thumb | ≈ 10% of intake | ≈ 284 kcal/day at maintenance |
The spread is honest. TEF depends on how much you eat (more food, more processing), what you eat (next section) and how it is measured — the review notes that the measuring conditions themselves, including how long the observation runs, change the figure1. Somewhere between 150 and 300 kcal a day is the right mental size for most adults.
In plain terms: eating costs a little energy, and that little energy is about a tenth of the meal.
By macronutrient
Not all calories cost the same to process. The review's finding is a clear ranking: the hierarchy of macronutrient oxidation after a meal is reflected in diet-induced thermogenesis, in the sequence alcohol, protein, carbohydrate, fat — with values higher on a relatively high-protein or high-alcohol intake and lower on a high-fat one1.
| Macronutrient | Energy per gram (the factors our calculator uses) | Relative thermic cost |
|---|---|---|
| Alcohol | 7 kcal | highest |
| Protein | 4 kcal | high — the main dietary determinant of TEF after total energy |
| Carbohydrate | 4 kcal | moderate |
| Fat | 9 kcal | lowest |
The reason is mechanical. Protein has to be broken into amino acids and either rebuilt into tissue or converted before it can be used for energy, both of which cost ATP. Fat is already close to its storage form and slides into adipose tissue cheaply. Carbohydrate sits between: cheap to burn, more expensive to store as fat.
What this means in practice is smaller than the marketing around it. Swapping a slice of a 2,800 kcal day from fat to protein raises TEF by tens of kcal, not hundreds. The review's more interesting point is about satiety — protein's thermic effect is linked to feeling full, which affects how much you eat next1 — and how much you eat is the term that actually moves the equation. Our macro calculator sets protein first for reasons of tissue retention and appetite, not because of the thermic bonus.
Why it is already inside your TDEE
This is the practical point of the article. Every TDEE estimate is built as BMR × activity multiplier, and the multipliers — ours run from 1.15 to 1.825 — were fitted to total daily expenditure, measured in people who were eating. The multiplier is not "exercise plus NEAT"; it is "everything above BMR", and TEF is in there.
| Layer of the estimate | Contains TEF? |
|---|---|
| BMR (Mifflin-St Jeor) | no — by definition, fasted and at rest |
| activity multiplier (1.15–1.825) | yes — fitted to total expenditure including meals |
| TDEE = BMR × multiplier | yes, once |
| "add 10% for TEF" | counts it twice |
So the arithmetic 2,837 + 10% = 3,121 is wrong by about 284 kcal — roughly the size of a modest deficit — and it is a common mistake in spreadsheets and forum posts. The same goes for adaptive expenditure estimates: a number read from your intake and weight trend (see how apps estimate energy expenditure) is a total, and totals include digestion.
The one place TEF legitimately enters a decision is at the margin: two diets at identical calories with very different protein will differ by a few tens of kcal in true expenditure. That is real, it is small, and the weight trend will absorb it without anyone doing the sum.
This is arithmetic on reference values, not medical advice. TEF is a component of expenditure to understand, not a lever to pull; the lever is intake.
The short version
The thermic effect of food is the energy cost of processing a meal — about 10% of BMR by the FAO/WHO/UNU figure, 5–15% of daily expenditure on a mixed diet by the research review, so roughly 150–300 kcal a day for most adults. Alcohol and protein cost the most to process, fat the least. It is already inside every TDEE estimate because activity multipliers were fitted to total expenditure — adding it again is a 250–300 kcal mistake. Educational overview only — not medical advice.