Protein and the Thermic Effect of Food

The Thermic Effect of Food (TEF) is one of the three major components of daily energy expenditure, the other two components being a) Basal Metabolic Rate and b) the energy cost of activity.  

The energy expenditure from TEF is related to the stimulation of obligatory energy-requiring processes associated with eating, digesting, absorbing, and storing food (as well as the facultative energy expenditure associated with hormone secretion, sodium-potassium ATPase pump activity, protein synthesis, and substrate recycling).

The TEF raise in metabolism spikes after meals, and gradually declines over ~10 hours (as determined by the return to Basal Metabolic Rate). The main determinant of TEF is the total energy content of the meal (total calories consumed), followed by the protein fraction of the meal.

When consuming a mixed diet TEF averages at about 10% of calorie intake.

For a "balanced" high-protein diet (35%/30%/35%, protein, carbohydrate, and fat respectively) TEF will be ~12% of calories ingested. (For perspective, 35% of calories as protein is the top end of the "acceptable" range for protein set by the National Academy of Sciences.) The TEF value for a more "extreme" high-protein diet (less carbohydrate and more fat) will lower total TEF, because fat has a lower TEF than carbohydrate.

The theoretical TEF values for separate nutrients are actually ranges, as TEF varies greatly between different sources of carbohydrate, protein, fat and alcohol:

Fat: 2 to 3%
Carbohydrate: 5 to 10%
Protein: 20 to 30%
Alcohol: 10 to 30% 

Some early data was mixed on how an energy deficit, or overage, affects the relative TEF following a meal. It has been theorized that excess energy intake raises TEF beyond what the calorie increase would seem to account for. Others have speculated that a predisposition to weight gain may include a suppressed TEF response. The majority of research on these questions has failed to to support either of these early theories.

Many authors of high-protein/low-carbohydrate diets claim that there is a "metabolic advantage" due to the higher TEF of protein. While it is true that for an equal number of calories the TEF will be higher on a high-protein diet, the difference is arguably not of practical significance because reduced-calorie diets have small TEF values.

For example, in the chart below for 1400-calories, the TEF would be 33-calories higher per day on a high-protein diet (35%Pro/30%Carb/35%Fat) versus a balanced diet (20%Pro/50%Carb/30%Fat). Based on that difference it would take around 100-days to lose one additional pound. (Calculations based on the average TEF values of the ranges noted above.)

The exaggerated claims regarding a "metabolic advantage" for high-protein diets may be based on confusion between postprandial thermogenesis (a single measurement 2.5-hours after eating) and the TEF response for the full meal which requires multiple measurements over 8- to 10-hours. Only the full meal TEF can reveal the actual magnitude of difference between two dietary regimes.

Please note that protein intake during weight loss (reduced energy intake) is of critical importance despite its modest effect on TEF. For details see: 5 Things you need to know about protein for healthy weight loss.

Other terms for the Thermic Effect of Food (TEF) are, Diet Induced Thermogenesis (DIT), and the now seldom used term: Specific Dynamic Action (SDA).

All the Best!
-Dorene

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References:
-Westerterp KR. Diet Induced Thermogenesis. Nutr & Metab 2001;1(5).
-Owen OE, et al. A reappraisal of caloric requirements in healthy women. Am J Clin Nutr 1986;44:1-19.
-Golay A. Similar weight loss with low- or high-carbohydrate diets. Am J Clin Nutr 1996;63:174-178.