The amount of energy that a particular food delivers to the body is measured in calories, a fact you might be all too familiar with if you have ever counted calories or tried to limit calories for weight loss. We burn calories simply by being alive! Every bodily function requires energy, so even when you are asleep, you are burning calories. Exercise requires more calories, which is one of the reasons why exercise can help you maintain a healthy weight. When we eat, our metabolic rate increases for a while. This means that we burn more calories. This is known as the thermic effect of food or TEF. Let’s look closer at this and see what it can tell us about our metabolism.
How is the Thermic Effect of Food Measured?
It is very difficult to measure the thermic effect of food. How the metabolism of an individual responds to eating food depends on many factors. The metabolism of each person is unique, and we all respond differently according to our state of health, lifestyle, and unique microbiome. This means that there is no single reliable method of calculating the precise thermic effect outside of a professional laboratory. However, some foods are known to have a higher TEF than others. These foods have been shown to increase the metabolism for longer than others, meaning that they could help burn more calories. This could be excellent news for those trying to boost their metabolism, burn more calories or simply make better food choices.
It is important to note that there are no foods that increase the metabolism to the extent that more calories are burnt off than are consumed! Sometimes people refer to zero-calorie foods, using the thermic effect to explain how they burn more calories than they contain. This is not accurate, and no foods have been proven to be calorie negative in this way. However, there are plenty of foods that are low in calories and plenty which have been shown to have a higher TEF.
Different foods have different impacts on the metabolism. The food group with the lowest thermic effect is fat, burning an estimated 0-3% of energy. Carbohydrates, which burn up to 10% of energy, have a higher thermic effect. However, the food group that stands out in terms of boosting metabolic rate is protein. Protein-rich foods can burn 20-30% of energy consumed. This is a short-term increase in metabolic rate; while it doesn’t increase your basal metabolic rate, the thermic effect of a protein-rich meal can last for several hours.
Protein-rich foods that may boost the metabolic rate include oily fish such as salmon (which also deliver lots of nutrition). Lean meat is a great source of protein, and eggs are a known thermic food that deliver protein and nutrition. However, there are plenty of plant-based protein sources of protein including tofu, tempeh, lentils, chickpeas, and nuts.
Processed Vs. Unprocessed Foods
When it comes to making good food choices, the thermic effect is another reason to ditch processed foods and choose unprocessed options. Unprocessed foods tend to be richer in essential dietary fiber that helps with the processes of digestion and supports a healthy gut microbiome. When we eat unprocessed foods, the metabolic rate is boosted more compared to when we eat processed foods. This suggests that eating foods that are in their natural state, and have not had fiber removed, could not only keep us feeling fuller for longer they could also help burn more calories through the thermic effect. This is just one more reason to choose whole grain options and swap white bread, pasta, and rice for the less processed brown versions.
How Important is TEF?
The thermic effect is an important part of our daily calorie burn, but it does only account for a small part of the overall expenditure of calories. So, it is important not to rely too heavily on this for burning calories; this is not a weight loss solution! It is much more important to take other factors into consideration, such as how much we are eating, what types of foods we are eating, and how active we are on a daily basis. It is much easier to increase the calorie burn by being more active than it is to increase it by relying on certain foods to temporarily increase the metabolic rate. However, one of the most interesting and useful factors is that an active lifestyle actually increases the TEF after we eat.
Physical Activity and TEF
Physical activity increases the thermic effect of food. In people who move around more, get more physical exercise, and are fitter, the thermic effect has been shown to be much higher after meals. This means that the key to using the thermic effect could lie with exercise as much as with food choices. A combination of making good food choices – including lean protein-rich foods, unprocessed foods, and plenty of dietary fiber – and getting lots of exercise could make a difference to the daily calorie burn.
How we eat, when we eat, the size of our meals, and what foods we choose all have an impact on our metabolism. We each have a different basal metabolic rate, and it changes as we age, generally slowing down. As well as this, we have the impact of exercise to consider. Exercise burns calories, but it also increases the thermic effect of food. While the thermic effect does change how many calories we burn, it is not enough to rely on this alone to burn calories or maintain a healthy weight. Maintaining a healthy weight requires a healthy lifestyle, so it is important to think about all aspects of your life.