TEF

TEF — thermic effect of food, sometimes called diet-induced thermogenesis — is the energy your body spends digesting, absorbing, and metabolising the food you eat. Eating costs calories. Roughly 10% of a typical mixed-diet intake is expended this way, with the remainder going to BMR, NEAT, and exercise.

TEF by macronutrient

• Protein: 20–30% of calories consumed. Protein is expensive to process — deamination, urea synthesis, and gluconeogenesis all cost ATP.
• Carbohydrates: 5–10%. Lower for simple sugars, higher when carbs are being converted to glycogen or (rarely, at large surplus) to fat.
• Fat: 0–3%. Dietary fat has the lowest metabolic cost to store as body fat, which is why the "a calorie of fat is easier to store" folk claim contains a grain of real physiology.
• Alcohol: around 15%. Higher than you'd expect because ethanol metabolism is unusual.

How this adds up

A sedentary person eating 2,400 kcal/day from a typical Western diet (around 15% protein, 50% carb, 35% fat) spends roughly 240 kcal processing food — so the intake that "counts" against their TDEE is around 2,160 kcal.

Shift to a high-protein diet — say 35% of calories from protein — and TEF rises to around 14–15% of intake, adding roughly 100 kcal/day of extra expenditure at the same total intake. This is a real effect and is one mechanism by which high-protein diets modestly favour fat loss beyond the satiety and lean-mass effects.

Why tracking apps don't show TEF separately

Most consumer apps — MyFitnessPal, Cronometer, Lose It!, MacroFactor — fold TEF implicitly into their TDEE estimate by using predictive equations that were fitted against real-world caloric balance. The "calories you burned today" number on your wearable also folds TEF in through the BMR component.

This means the calorie deficit displayed by your app is already accounting for TEF on average. You are not missing calories.

Where TEF drift can matter

If you make a large macro shift — going from 15% protein to 35% protein overnight — TEF rises noticeably and your real maintenance calories rise with it. An app that re-estimates TDEE adaptively from your weight trend will catch this. An app that sticks to the initial predictive-equation TDEE will slightly underestimate your maintenance going forward.

The practical leverage

The strongest lever on TEF is total protein intake. Moving from a low-protein diet (around 0.8 g/kg) to a high-protein diet (around 2.0 g/kg) at the same calorie target produces a real expenditure bump of 50–100 kcal/day and a measurable satiety improvement. This is why "eat more protein" keeps reappearing as an evidence-based recommendation across deficit, maintenance, and surplus contexts — the TEF effect compounds with the satiety effect and the lean-mass-preservation effect, in the same direction, for essentially no side-effect cost.