What is the Thermal Effect of Food?
Wouldn’t it be great if you could burn calories by consuming calories – therefore by eating food? Gosh, that would seem like the ideal way to control your weight if that were possible. Eat and lose weight. Well, guess what? You can burn calories by eating foods. This doesn’t mean you will lose weight by simply eating. But, it means that by selecting the right foods you can expend some additional calories without taking in more calories. All solid food requires calories or energy in order to be digested and absorbed by the gut and delivered to the blood stream. The caloric cost of this process is known as the thermal effect of food. The thermal effect represents the increase in metabolism following ingestion of a meal. We discussed it briefly in How Many Calories Are in a Pound? [We Are Not Sure]. Today we are going to discuss this further as you can use the thermal effect of food to better control your weight.
The Thermal Effect of Macronutrients
There are three macronutrients: carbohydrates, protein, and fats. Each of these have a different thermal effect. The thermal effect of food is affected by how easy or difficult a food or macronutrient is to breakdown. Foods that are harder to breakdown have higher thermal effects meaning it takes more calories or energy.
So what is all required to break food down. Some foods require extensive chewing and chewing involves burning calories. Once the food enters the stomach hydrochloric acid is released which starts to break food down further, plus the churning and contractions of the stomach mechanically break food down further and also consumes calories.
Food then enters the duodenum or first part of the small intestine where various emulsifiers and enzymes released by the gall bladder and pancreas come in contact with food breaking it down and dissolving it even further. Finally, food is broken down into particles small enough to be absorbed by the remainder of the small intestine and enter the blood stream to be delivered to all parts of the body. As you can probably now appreciate better there is definitely energy being expended to digest food. So why not use that to your advantage?
Liquids do not require much work to break down in comparison to solids and we sometimes hear that liquid calories are different from solid calories and one reason for that is due to lower their lower thermal effect.
Here are the thermal effects for the macronutrients.
- Protein has a thermal effect of 30%
- Carbohydrates have a thermal effect of 5% to 15%
- Fats have a thermal effect of 0% to 5%.
First, what do these percentages mean? It means for every 100 calories of protein you consume 30 calories are burned just to digest and absorb the protein. Secondly, these percentages make sense based on the processes we just discussed describing how food is broken down.
Protein has to be chewed more than the other foods and it has to broken mechanically by the stomach to a greater extent than fats or carbohydrates. It takes more work or calories to prepare protein for absorption. Because it’s harder to break protein down in the stomach protein lingers in the stomach longer. This is one reason why proteins provide a greater sense of satiety or fullness limiting our tendency to overeat.
The range of thermal effects for carbohydrates is explained in part by the fiber content in carbohydrates especially indigestible fiber. Some foods like celery are said to have a negative calorie balance. Such foods are thought to take more calories to breakdown than the number of calories they contain but this has not been proven in studies. Below is a list of such negative calorie foods. It is likely they contain more calories than it takes to digest them, but incorporating them into your diet is a way to improve your caloric balance.
Negative Calorie Foods
- Cantaloupe/honey-dew melons
- Green beans
These “negative calorie” foods are fruits and vegetables with berries and cruciferous vegetables heading the list. They all have higher amounts of fibers and are relatively calorie sparse in comparison to starchy carbs.
To improve your metabolism consume more protein focusing on lean red meat, fish, chicken and turkey, and eggs. Make fruits and vegetables the focus of your carbohydrate intake, too.
Napoleon Hill wrote a book, Think and Grow Rich. By choosing foods with high thermal effect you might not be able to Eat and Become Thin but you should become thinner.
Live long, stay young!