Apart from the resting metabolism and energy expenditure during physical activity, the body also burns calories every time you eat. This is referred to as the Thermic Effect of Food ( TEF), or the Thermogenic Effect of Food.
After you eat, your energy expenditure increases for about 4 to 8 hours, as your body breaks down the food that you have eaten and prepares to store the nutrients in your body. It’s this period of time where your TEF comes into play. So, it is essentially one of the components of your daily caloric expenditure besides your BMR (Basal/resting metabolic rate) and your energy expenditure during any activity or exercise.
All foods have a thermogenic effect, but the effect may be low or high depending on the extent of digestion and metabolism required for the breakdown of the foods consumed. This does not mean that the food you eat burns fat. It simply means that TEF is the energy expenditure (calorie burn) for digestion of the food. Therefore, eating high thermic foods can contribute to an increase in the calorie burn.
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. For 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 TEF:
- The amount of Carbohydrates, Proteins and Fats that you eat in your meal (protein costs the most energy to use and store, followed by complex carbs, followed by fats).
- The caloric content of your food.
- Your individual diet, i.e the specific things that you eat and its quantity. What is the intake of fruits, veggies, processed foods & sugars in your diet.
- Your age also influences your TEF. It reduces with age, unless, food intake reduces or physical activity increases. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4366678/)
Contribution of Thermogenic Foods in Weight Loss:
Thermogenic foods may help increase metabolism and calorie burning by enhancing Thermogenesis, a process in which the body burns calories to utilise the foods you have just eaten, converting those calories to heat.
When you eat food, your body must expend some energy (i.e. calories) to digest, absorb, and store the nutrients in the food that you have eaten. Therefore, as a result of the thermic effect of food, by consuming high thermic foods, you actually increase the rate at which your body burns calories.
Consuming difficult to digest foods (thermogenic foods), will cause your body to shed extra calories during the process of digestion.
Protein is actually the hardest food for your body to process and utilise. This is one of the best reasons to eat sufficient protein with each meal. It can cause 20 to 35% calorie. Carbohydrates cause 5 to 15% calorie burn. Fats(lipids) cause only 0 to 5% calorie burn. This is why fat in excess, tends to go right onto your waistline.
Example: If you eat 200 calories worth of protein, your body will use between 40 and 70 of them in digestion. If you eat 200 calories worth of fat your body will use between 0 and 10 of those calories during digestion. If you eat 200 calories worth of carbohydrates your body will use between 10-30 of those calories during digestion.
Keep in mind that if you are trying to lose weight, it does not make sense to increase your meal size to augment the thermic effect of food. At the end of the day, only overeating makes you fat.
The following table will give you an understanding of examples of some Low and High Thermogenic foods:
Although the word thermogenic means heat generating, thermogenic effect of food refers to the increase in the BMR, not an increase in heat in the body. It must not be mistaken for certain foods thought to generate heat in the body and lead to rashes and boils.
If it does, it is an individuals allergic reaction to that particular food and cannot be generalised to the whole population.
In conclusion, while TEF can help in weight loss at a minimal level, it is best to understand, that 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.