TEF or the thermic effect of feeding is the increase in your body’s thermogenesis following a meal. Every time we eat a meal our basal energy expenditure increases due to the cost of digestion. It is for this reason that meal frequency isn’t actually all that important as much as the total calories consumed in a day! Although we are account for TEF in terms of non resting energy expenditure this only accounts for a small percentage of total daily energy expenditure!
Why is TEF important?
TEF is important because it affects your total daily energy expenditure! By ensuring you are eating the right proportion of macronutrients in your diet can help you expend more calories during the day. Research shows that protein-rich foods increase TEF the most, larger meal sizes opposed to frequent small meals increases TEF as well as age and physical activity can play a role (1).
Of all the macronutrients, protein has the highest thermic effect of feeding. Approximately 30% of the calories consumed from protein are used toward digestion. That means if you consume 100 calories from protein, roughly 30 calories will go towards digestion and the remaining 70 calories will be metabolized and used as fuel. The thermic effect of carbohydrates is about 10-15% and dietary fat is between 0-10%, depending on the type of fat. The thermic effect for mixed meals is typically around 10-15% (3).
In essence, what this means is that of ALL macronutrients, we are LEAST LIKELY to store excess calories from protein, followed by carbohydrates and then dietary fats. This also explains why, when matched for calories, low carbohydrate diets typically yield slightly greater weight loss compared to isocaloric high carbohydrate diets. Previously, we believed this so-called metabolic advantage associated with low carb diets was due to the lower insulin response. We now know the metabolic advantage was due to the higher protein intake associated with low carb diets, which yields a higher thermic effect.
Studies also show that overconsumption of high fat leads to MORE body fat gain than overconsumption of high carbs. This shows that it is not insulin but TEF that affects the degree of weight loss or gain in response to different macronutrients (4).
Clean Health Fitness Institute. (2020). Performance Nutrition Coach Level 2. CHFI.
Antonio, J, et al. (2015). A high protein diet (3.4 g/kg/d) combined with a heavy resistance training program improves body composition in healthy trained men and women–a follow-up investigation. Journal of the International Society of Sports Nutrition.12 (39).
Horton TJ, et al. (1995). Fat and carbohydrate overfeeding in humans: different effects on energy storage. American Journal of Clinical Nutrition. 62(1):19-29.