Thermic Effect of Food

Thermic effect of food, a term commonly heard in fitness circles. Let's see what we can learn and how it can help us.

We've all seen and used calorie calculators, caloric balance formulas etc. They give us the number of calories we need to maintain our weight. They include abbreviations like BMR/RMR, TEA, NEAT and TEF. In this article I will specifically talk about the latter.

What is it?

TEF or thermic effect of food is a parameter indicating how much of the energy/caloric value of a food is necessary for its adoption and absorption.

For example after eating protein, your liver has to degrade it to amino acids, carbohydrates on the other hand have to be degraded to glucose. All this consumes energy and this exact process is known as a thermic effect.

TEF is a very small part of the equation for energy balance, and like some other things, it's a dynamic parameter (it's not constant)

It differs not only from person to person, but also in different macronutrients. It was found that in overweight people the thermic effect was significantly weaker.

Losing the extra pounds can return levels to their normal range. This also often explains the insulin resistance caused by too much body fat. Overweight individuals might have the effectiveness of their TEF halved.

In other words, if a diet consists of 3500 calories, and say 350 are (in normal circumstances) burned on food processing, a 50% loss would mean 175 less calories burned every day. In a period of one month that accumulates to 5250 calories, which is about 0.75 kg(1.65 lbs) of fat gained every month.

How do we measure TEF?

We mentioned what it represents. It's also defined as the difference between the energy expenditure of the body before and after a meal. This is exactly how it's actually measured. Digestion is a long and complex process and its duration is an important factor for the calculation of the thermal index.

An American group of scientists made 131 tests on different individuals, giving them foods with different portions and compositions. The entire test lasts 6 hours. The results were proportionally related to portion size and the individuals lean body mass (LBM)

The conclusion is that the thermic effect lasts for about 6 hours and it is directly related to the amount of food. In other words the more food you eat, the more energy and time will be expended for its digestion.

What are the typical values?

Protein - here the TEF is the strongest. Depending on the type and composition of the protein it varies between 20-30%.

Carbohydrates -  here we also have a pretty big difference, the TEF values are between 5% and 25%, most of the time it tends to be on the lower side.

Fat - around 2-3%. This effectively means that our body doesn't lose energy while processing fat and can simply store it in the same condition in which it was eaten.

In general, the accepted average value is 10%. Because of this, it's considered that 1/10 of the total energy balance is due to the TEF. Generally, more protein = stronger thermic effect. Fiber also helps.

It's important to note that TEF doesn't depend on the number of meals per day, all that's important is the amount and type of food eaten. If you eat three 1000 calorie meals(3x1000=3000 x 10% =300 calories) or six 500 calorie meals(6 x 500=3000 x 10= 300 calories) the energy expenditure will be the same. So number of meals/meal timing does not matter.

Thermic effect and calories in different foods

Since this is a parameter that varies in different macronutrients and their combinations it isn't included in the Nutrition Facts of most foods. As you know proteins and carbohydrates are about 4 calories and fats around 9 calories/gr. This of course shouldn't be a cause for concern, as TEF is compensated for in the equation for energy intake.

An interesting fact is that if you need 2500 calories/day to maintain your weight, but you choose to not eat anything for a day, in theory that number will drop to 2250.

Can we manipulate it in order to lose fat?

We've got two options here, controlling appetite and burning extra calories by substituting foods with a low TEF for foods with a high TEF.

First option: It has been proved that foods with a stronger thermic effect are more satiating. In practice, this means that high protein diets are more satiating and if you have problems with hunger and appetite, by increasing the amount of protein in your diet at the expense of carbohydrates and fats, you will tame your hunger.

Second option: Changing the main source of energy in a certain diet will have an effect on its caloric balance. In an experiment where 3 diets were compared, each of which had it's total caloric value of about 70% from a different macronutrient respectively, protein, carbohydrates and fats.

The extra calories burned in the first diet(70% protein) were about three times more than the other two.

To show how this could affect you personally, let's take two extreme examples to compare and see which wields the maximum benefit (in normal circumstances the numbers will never be so high) and make a conclusion.

Let's say that you consume 200 calories from fat. You decide to replace those fats with protein instead. To demonstrate the theoretical maximum we will use extreme values.

TEF of fats is 3%, protein - 30%. In this case the the extra calories burned will be respectively 6 and 60 cal. The difference is 54 cal. If we do the same with carbohydrates instead of protein, the difference will be in the range of 8-10 cal. Neither is significant, nor practical.

For it to have a real impact, you'll need to manipulate macronutrients in scale, and that is rarely possible for various reasons (taste, cost, load on the liver etc.) It's not something anyone should worry about.

The thermic effect of food is a part of the energy balance equation. And that, like other parameters changes from person to person, diet and even lifestyle.Which reminds us once again that the calorie balance formulas only give us an approximate number.

You could use the TEF to manipulate the caloric balance, but that wouldn't bring significant enough results.
The only practical "use" of foods with a strong thermic effect( in my opinion ) is that those foods are more satiating and can really help out with hunger and satiation when cutting.

Good luck!