Daily energy expenditure consists of three parameters: basal metabolic rate (energy required to keep your body functioning at rest), thermic effect of food or diet-induced thermogenesis and the energy cost of physical activity. By definition “Thermic effect of food (TEF) or dietary induced thermogenesis (DIT), is the amount of energy expenditure above the resting metabolic rate due to the cost of processing food for use and storage.” In other words, to get the energy out of the food we ingested, we must first utilize some energy to digest, absorb and transport the food’s nutrients to the body’s cells. Some components of our food have a greater impact on TEF than the others and after each meal, our metabolism increases.
Protein Intake and TEF
We all know proteins are building blocks of our body and tissues. Most of the people are aware of fact that proteins are important in the building of our immune system (immunoglobulins or antibodies), hormones, enzymes, transport proteins and neurotransmitters. People involved in food science and nutrition will also emphasize protein’s effect on satiety. Protein generally increases satiety to a greater extent than fats or carbohydrates and may cause a reduction in overall energy consumption.
But what occupied my mind only recently is the fact that compared to carbohydrate and fat, protein has the highest thermic effect of food (TEF).
In order to process a protein meal, you will burn around 30% of the calories just to digest the meal. The other two macronutrients, carbohydrate and fat, have lower thermic effect: carbohydrate digestion will cause 15 to 20 % and fat 2-3% of the calories expenditure. This means most easily digested are fats.
I was particularly interested in the influence of dietary fiber on thermogenesis. To my surprise, a high-fiber meal causes a lower thermic effect of food than a lower-fiber meal. It is believed that the lower thermogenesis associated with fiber is partially caused by fiber’s slow absorption of glucose and reduced insulin response which is required for insulin-related glucose disposal. So the dietary fiber content present in food does have an impact on the overall energy expenditure.
The TEF and Obesity
There is a connection between the body fat percentage and the thermic effect of food. Some studies reported a decreased thermogenesis in the subjects who are obese when compared with those who are lean. The reduction of TEF in obese subjects is most probably related to the degree of insulin resistance and decreased activity of the central nervous system. Even more, the greater the degree of insulin resistance, the smaller the thermic effect of food. But the good news is, obese individuals with insulin resistance can use exercise to increase the TEF. It was shown that exercise affects TEF more in the obese individuals with insulin resistance than the less-resistant subjects.
The reduction of TEF has also been found in previous obese individuals after weight loss. These individuals showed overall reduced energy expenditure. The decrease in the thermic effect of food, along with other factors as lower resting metabolic rate and restricting caloric intake, may be one of the factors favoring the relapse of obesity after weight loss.
How to Use the Thermic Effect of Food to Boost Your Metabolism
In conclusion, diets higher in protein result in an increased weight and fat loss when compared to diets lower in protein. So, for those who try to lose some weight, it is recommended to partially replace refined carbohydrate (for example white bread and pasta, candies, soft beverages, etc) with protein sources that are low in saturated fat (like egg whites, lean meat, salmon, tuna, etc.).
Some food and beverages may help to enhance the thermogenesis. Consuming foods with spices (like black pepper, cinnamon or red hot peppers) and some beverages (like green tea and coffee) can increase thermogenesis and may affect feelings of satiety and contribute to fat oxidation. There are plenty of supplements on the market containing these substances. However, they do not have a significant effect on weight loss. Cutting calories from everyday diet and exercising more regularly are still our best bets.