Thermic Effect of Food
Thermic Effect of Food — The thermic effect of food (TEF), also called diet-induced thermogenesis, is the energy the body expends to digest, absorb, and metabolize ingested nutrients. TEF accounts for approximately 10% of total daily energy expenditure on a mixed diet, but the percentage varies by macronutrient: protein costs 20-30% of its energy, carbohydrate 5-10%, and fat 0-3%.
What is the thermic effect of food?
The thermic effect of food (TEF) — also termed diet-induced thermogenesis (DIT) — is the increase in metabolic rate that occurs after eating. It represents the energy cost of:
- Mechanical and enzymatic digestion in the GI tract
- Absorption across the intestinal lining
- Hepatic processing of newly absorbed nutrients
- Synthesis of storage forms (glycogen, triglycerides, protein)
On a typical mixed diet, TEF accounts for approximately 10% of total daily calorie intake. It is one of the four components of TDEE, alongside BMR, structured exercise, and NEAT.
How does TEF differ by macronutrient?
TEF is markedly different across the three macronutrients, based on synthesized values from controlled feeding studies (reviewed by Westerterp, 2004):
- Protein: 20-30% of ingested calories spent on TEF
- Carbohydrate: 5-10% of ingested calories
- Fat: 0-3% of ingested calories
- Alcohol: 10-30% of ingested calories
A meal of 100 kcal pure protein delivers approximately 70-80 kcal of net energy after TEF, while 100 kcal of pure fat delivers 97-100 kcal net.
Why TEF matters in weight management
TEF is one mechanism by which higher-protein diets favor body composition during weight loss. A diet of 30% protein vs. 15% protein at the same total calorie intake delivers meaningfully fewer net usable calories, on the order of 80-150 kcal/day for a typical adult diet. Over weeks and months this compounds.
Additional practical implications:
- “Negative-calorie food” claims (celery, lettuce) are largely myth — TEF rarely exceeds the energy content of any whole food
- Frequency of meals does not materially change 24-hour TEF: total daily protein and total daily calories matter, not whether they were split into 3 meals or 6
- Highly processed foods may have modestly lower TEF than less-processed foods of equivalent macronutrient composition, per Barr & Wright, 2010
See related entries on BMR and TDEE.