Protein Burns More Calories Than Carbs. The Long Run Is Less Clear.

Protein burns more calories to process than carbohydrates or fat. The numbers have circulated through fitness content for years: roughly 20 to 30 percent of protein's calories are spent during digestion, compared to 5 to 10 percent for carbs and close to zero for fat. Those are the figures usually quoted. The 2024 review of 52 studies this Short draws on never gives one for protein; it says digesting food, of every kind, accounts for about 10% of the calories burned in a day.

Nobody asks what happens after the first week.

Does Protein Burn More Calories Than Carbs?

After a meal, yes. A 2024 meta-analysis of 52 studies found that higher-protein meals produced significantly more heat after eating than lower-protein meals, and raised the total calories burned in tests lasting a day or two. The studies disagreed widely, though: the extra heat was significant in the leaner half of the studies and in the younger half, but not in the other halves.

What happens on longer diets is where the evidence thins.

In the short term, the extra burn appears to come from handling the meal itself. One explanation the authors offer is that a protein-rich meal sets off protein building in muscle and other tissues, which takes energy and shows up as heat in the hours after eating. This is the thermic effect the infographics describe: the immediate, per-meal burn.

On longer diets, the picture changes. In 13 studies of longer-term diets, the extra heat after a meal was no longer significantly higher on the higher-protein diet. The authors raise the possibility that the body adapts, and say more studies would be needed to confirm it. If the story ended there, the talking point would be half-true: protein burns more per meal, and on a longer diet that edge no longer shows.

How big could that be in calories? The review points to one trial whose effect size was similar to the pooled result for longer diets; it measured a day in a respiration chamber, and total daily burn was 72 calories higher on the higher-protein diet, about 3%. Researchers estimate that 10 to 20 extra calories a day explain the average yearly weight gain of US adults, so that one trial's gap is 3.6 to 7.2 times larger. The authors conclude a protein-rich diet could help limit weight gain if the extra burn is not fully offset by eating more.

One caveat the data earns: the extra heat after a meal was significant in studies of people at a normal weight, not in studies of people with overweight or obesity, and the authors say it is not clear whether that is a true difference or a result of how the studies were run. On longer diets, the rise in resting metabolism was significant only in studies with an average BMI below 29.75, not at or above it.

A second finding from the same review: it found no evidence that the type of protein changed energy expenditure. That rests on a few small comparisons (whey against no whey, fish against red meat, mixed animal and plant protein against plant protein alone), and the authors ask for caution. The supplement shelf implies a hierarchy; this evidence does not show one.

So the infographic's headline holds for a single meal: protein costs more to process. The part nobody included was the timeline. On longer diets the evidence is thinner and less certain, and the move from digestion to resting metabolism is the authors' hypothesis, not a measured result.

One trial raises the next question. Resistance-trained men and women who pushed their protein to 4.4 g per kg of body weight a day, eating about 800 more calories a day, for 8 weeks showed no significant change in body fat. The authors suggested protein's high thermic effect might be one reason, but they measured body composition, not calories burned, and food intake was self-reported. That open question sits behind what happens to protein the body can’t use.