Some of the calories in the food you eat are used to digest, absorb, metabolize, and store the remaining food, and some are burned off as heat. This process is known under various names, notably diet-induced thermogenesis (DIT), specific dynamic action (SDA), and the thermic effect of food (TEF).
The TEF represents about 10% of the caloric intake of healthy adults who eat a standard mixed-macronutrient diet, but your actual number will depend on several factors, including your age and the meal timing, and macronutrient composition — carbs, fat, and protein — of your meal. The energy required to digest each macronutrient (its TEF) can be expressed as a percentage of the energy provided by the macronutrient:
Fat provides 9 calories per gram, and its TEF is 0–5%.
Carbohydrate provides 4 calories per gram, and its TEF is 5–10%.
Protein provides 4 calories per gram, and its TEF is 20–30%.
Resting metabolic rate (RMR) refers to the amount of energy used while the body is at rest. To put it another way, it’s how many calories your body would use if you were lying down all day. The TEF is related to this measure, as it refers to the increase in RMR after the consumption of food and accounts for about 10% of daily energy expenditure, as we noted above.
There are several methods used for measuring the TEF, as seen in the table below. All come with varying degrees of complexity, cost, accuracy, and reliability. These measurements must be done in a laboratory or clinical setting with specialized equipment and trained technicians.
Adapted from Calcagno et al. J Am Coll Nutr. 2019.
Aside from a protein supplement, such as whey protein, no other supplements we’ve reviewed have had a notable effect on the TEF in either direction — increase or decrease. The table below displays an analysis of human studies and indicates how supplements may affect the TEF.
A common claim is that more frequent meals create a higher total TEF over the course of a day, which can lead to greater fat loss. Consuming a single, giant meal will produce a greater thermogenic response than having a smaller meal, but if the TEF of all the small meals were added up, there looks to be no meaningful difference from a single, giant meal.
This has been demonstrated with one vs. two meals, two vs. three meals, and two vs. seven meals. A study in humans — and an earlier study with dogs — showed a thermogenic benefit from higher meal frequency, but the bulk of evidence shows no TEF difference among meal frequencies.
In one study (analyzed here in NERD), 20 healthy volunteers consumed a standardized meal at 8 a.m. or 8 p.m., and their metabolic response was measured. Eight hours before having the meal, participants consumed a slightly smaller standardized meal and were asked to spend the following six hours in bed. Values for the TEF were higher after the morning meal (328 kcal) compared with the evening meal (237 kcal).
This is consistent with previous research that reported a 31% relative decrease in the TEF after an evening meal, compared with one in the morning.
As expected, meals higher in protein produce a higher TEF compared with those lower in protein. But what about high-carb vs. high-fat meals? Most evidence, though scarce, points to high-carb meals producing a greater thermic effect when compared with high-fat meals.
The TEF response may actually be blunted in people with obesity or insulin resistance (which excess body fat can contribute to). These small differences can add up over time. It is not clear just how much these conditions affect the TEF, though, as the research to date is not sufficient to confidently answer this question.
One study has suggested that physical activity, regardless of age or body composition, can increase the TEF. The study compared active and sedentary men in a younger and older population. The TEF was higher in the active, younger group (323.42 vs 222.17 kcal) and the active, older group (292.04 vs 215.47 kcal) compared with their respective sedentary age counterparts.
Three studies have shown that the TEF may decrease as you age. The largest, which had 123 participants, found that the TEF was about 1% lower in older subjects (60–88 years old) compared with younger ones (18–35). Two smaller studies have also produced similar results.