Thermic Effect of Food
What is the Thermic Effect of Food? Implications of the Thermic Effect of Food on Metabolic Rate Factors that Influence the Thermic Effect of Food Influence of Meal Size on the Thermic Effect of Food Influence of Meal Frequency on the Thermic Effect of Food Influence of Meal Composition on the Thermic Effect of Food Influence of Meal Pattern on the Thermic Effect of Food Influence of Body Composition on the Thermic Effect of Food Final Thoughts on the Thermic Effect of Food
What is the Thermic Effect of Food?
The thermic effect of food, also known as diet-induced thermogenesis or postprandial thermogenesis, is a reference to the increase in metabolic rate (i.e. the rate at which your body burns calories) that occurs after ingestion of food. When you eat food, your body must expend some energy (i.e. calories) to digest, absorb, and store the nutrients in the food you've eaten. Therefore, as a result of the thermic effect of food, by consuming calories you actually increase the rate at which your body burns calories.
Implications of the Thermic Effect of Food on Metabolic Rate
So how does the thermic effect of food affect your overall metabolic rate? Based on the definition provided above, we already know that the thermic effect of food will increase your metabolic rate, but the real question is "How much calorie burn does the thermic effect of food account for?" Well, the general consensus in the scientific community is that the thermic effect of food accounts for roughly 5 to 10 % of the energy content of the food ingested. This would mean, for example, that if you eat a 400 calorie meal, you can reasonably expect somewhere between 20 to 40 calories to be burned in the process of digesting, absorbing, and storing the nutrients from the meal. Or, as another example, if you eat 2000 calories per day, roughly 100 to 200 calories will be burned each day as a result of the thermic effect of food.
Factors that Influence the Thermic Effect of Food
There are many factors that influence the magnitude of the thermic effect of food. These factors include things that are under your control, such as meal size, meal frequency, meal composition, meal pattern, and body composition, and things that are not under your control, such as age, gender, hormone levels, and genetics. For the purposes of this article we'll put aside discussion of the thermic effect of food factors that are not under your control, and focus on those that are.
Influence of Meal Size on the Thermic Effect of Food
There is a direct correlation between meal size and the thermic effect of food. The more calories there are in a meal, the greater the thermic effect of food will be as a result of consuming that meal (assuming that the relative proportions of protein, fat, and carbohydrates remain the same in each meal). This is no surprise, since the thermic effect of food is caused by the digestion, absorption, and storage of consumed nutrients. If you consume more nutrients, it follows that your body will need to expend more energy to process them.
Keep in mind that if you are trying to lose weight it does not make sense to increase your meal sizes to augment the thermic effect of food. Given that your weight is ultimately dependent on your caloric balance (read more about caloric balance in our Calories Explained article), increasing your meal sizes will ultimately result in an overall greater calorie consumption despite the slight increase in calories burned through the thermic effect of food. For example, if you were to eat a 500 calorie meal, 50 calories (or 10%) would be expected to be burned due to the thermic effect of food, so you would have a net calorie consumption of 500 - 50 = 450 calories. If you double the size of the meal to 1000 calories, 100 calories (or 10%) would be expected to be burned due to the thermic effect of food, so you would have a net calorie consumption of 1000 - 100 = 900 calories. In the end, you might have doubled the thermic effect of food from 50 calories to 100 calories, but you have also doubled your net calorie consumption from 450 calories to 900 calories, so you will still gain weight.
Kinabo JL, Durnin JV. Thermic effect of food in man: effect of meal composition, and energy content. Br J Nutr. 1990 Jul;64(1):37-44.
Influence of Meal Frequency on the Thermic Effect of Food
Experimental studies have shown that the thermic effect of food is larger when a set amount of calories are consumed as one single meal, rather than broken up into many smaller meals eaten over a longer period of time. For example, a 750 calorie meal eaten in 10 minutes would result in a higher thermic effect of food than the same 750 calorie meal eaten in six equal portions of 125 calories at 30 minute intervals. In the study referenced below, the difference in magnitude of the thermic effect of food, expressed as a percentage of the total calories ingested, was roughly 2% higher when the calories were consumed in one single meal.
Tai MM, Castillo P, Pi-Sunyer FX. Meal size and frequency: effect on the thermic effect of food. Am J Clin Nutr. 1991 Nov;54(5):783-7.
Influence of Meal Composition on the Thermic Effect of Food
The thermic effect of food due to a meal will vary depending on the relative proportions of the macronutrients (i.e. fat, carbohydrates, and protein) that make up the meal. Without a doubt, protein is the macronutrient that induces the largest thermic effect of food response. Roughly 25% of the calories in pure protein will be burned after consumption due to the thermic effect of food. Fat and carbohydrates, on the other hand, each induce a burn of roughly 5% of the calories consumed due to the thermic effect of food. So, for example, if you consume 400 calories of pure protein you will burn 100 (or 25%) of those calories through the thermic effect of food. If you consume 400 calories of pure fat or pure carbohydrates, only 20 calories (or 5%) will be burned through the thermic effect of food.
Influence of Meal Pattern on the Thermic Effect of Food
An irregular meal pattern (i.e. 3 meals on one day, 9 meals the next day, 6 meals the next day, etc...) has been shown to induce a significantly lower thermic effect of food than a regular meal pattern (i.e. a consistent 6 meals per day) that has the same total amount of calories.
Farshchi HR, Taylor MA, Macdonald IA. Decreased thermic effect of food after an irregular compared with a regular meal pattern in healthy lean women. Int J Obes Relat Metab Disord. 2004 May;28(5):653-60.
Influence of Body Composition on the Thermic Effect of Food
Body composition, or more specifically body fat percentage, has been shown to be a significant determinant of how active the thermic effect of food will be within a given individual. Lean people have a thermic effect of food that is approximately 2 to 3 times greater than obese people during rest, after exercise, and during exercise.
Segal KR, Gutin B, Albu J, Pi-Sunyer FX. Thermic effects of food and exercise in lean and obese men of similar lean body mass. Am J Physiol. 1987 Jan;252(1 Pt 1):E110-7.
Final Thoughts on the Thermic Effect of Food
Given all the information above, it seems as though you truly can increase your metabolic rate by adopting habits that will enhance the thermic effect of food. But the question is, should you do this? To be honest, it is really not worthwhile to make modifications to your eating habits with the sole intent of optimizing the thermic effect of food. If you managed to do it the effects would be minimal at best. A combination of healthy diet and exercise, to control your caloric balance, is always the best approach to losing and/or maintaining a healthy weight.