We all know what we should be eating—more fruits and vegetables, lean proteins, good fats and so on. We also know we should avoid junk food and keep a check on calories. However, what we eat and how it impacts our body goes way beyond these basic concepts. It isn’t just as simple as calories in, calories out as social media influencers might have you believe. In reality, if you ate 100 calories of pure sugar and 100 calories of lean protein, the two foods would have very different effects on your metabolism. Why is that, you may ask?
The answer lies in the ‘Thermic Effect of Food’ or ‘TEF’, also known as ‘Dietary Induced Thermogenesis’ (DIT) or ‘Specific Dynamic Action’ (SDA). This refers to the amount of energy our body needs to digest, absorb and metabolize the food that we eat. We can also think of it as the increase in energy expenditure above the resting metabolic rate that follows the ingestion of a certain kind of food. Let’s dive deeper into this highly important, yet often overlooked concept and see what factors influence it.
- The thermic effect of food is the energy your body burns as a result of digestion. Protein burns the most calories for digestion, followed by carbohydrates and then fats,
- The more processed or cooked the food is, the less effort your body has to put in to digest it, meaning fewer calories burned,
- Other factors influencing the thermic effect of food include the addition of certain spices and the state of the food consumed – i.e. if the food is raw or cooked (with raw foods requiring more energy for digestion).
What is the thermic effect of food?
More than just how many calories you eat, what you eat matters. Different types of food require different amounts of energy to be digested and absorbed by our bodies, so the good news is that some of the calories you eat actually get burned off in this process. In fact, TEF accounts for about 10% of the daily caloric intake for the average healthy adult on a balanced diet! Making careful choices here can therefore yield huge results towards your fitness goals.
If we consider different food groups, fat, carbohydrates and protein all vary in the amount of energy that is required to break them down. Fat, which provides 9 calories per gram, takes about 0-3% of the caloric value to be digested. Carbohydrate provides 4 calories per gram and has a TEF of 5-10%. Protein also provides 4 calories per gram and has a TEF of 20-30%, making it the most calorie-burning food category to be digested.
So, choosing a diet richer in protein and lower in carbs and fat may help you burn more calories, even if you ate the same number of calories as before. Carefully selecting higher thermic effect foods can help you boost your metabolism i.e. the rate at which your body burns calories.
What foods have a high thermic effect?
There are a number of high thermic effect foods that you should be eating to boost your metabolism. These are:
1. High protein foods
As mentioned before, higher protein foods require more energy for digestion. This means lean meats, low-fat dairy (such as skim milk, cottage cheese, Greek yoghurt or fermented dairy), eggs and fish are excellent metabolism-boosting choices. When 25–30% of your total daily calories come from protein, you may stand to burn an extra 80–100 calories per day as compared to lower protein diets. As a bonus, they also provide a higher degree of satiety due to protein’s ability to keep blood sugar levels stable, thus avoiding hunger pangs.
However, protein can be a little harder to digest and place a greater demand on the kidneys, hence be careful not to go overboard! Most official nutritional organizations recommend about 0.8 grams of protein per kilo of body weight per day as a starting point to avoid deficiencies, whilst those having more active lifestyles might want to aim a little higher.
2. High-fibre foods
Other than protein-rich foods, high-fibre foods are also an excellent choice as fibre slows the absorption of foods, keeping you fuller for longer. Since fibre can’t actually be digested, our bodies must work harder to separate it from the other nutrients, resulting in a higher thermic effect. Thus, fibre-rich foods such as lentils, and whole grains and fibre-rich fruits and vegetables such as pears, apples, bananas, carrots or broccoli are excellent choices.
The effect of fibre can also help us understand why higher-fat foods such as nuts, seeds and avocados are good choices – this is because, despite their high-fat content, these offer high amounts of fibre. Highlighting the effect of fibre in increasing the thermic effect of food, a 2017 study found participants increased their metabolism by more than 92 calories per day when they swapped out refined grains for whole grains!
3. Raw foods
Raw foods, which are harder to digest when compared to their cooked versions and offer more fibre, also have a higher TEF. So, the same carrot when eaten raw would actually yield fewer calories than when it is cooked, purely as a result of the calorie burn that comes from the body having to break it down. Of course, that is not to say that cooked foods should be completely shunned—rather, cooking may actually result in more nutrients being available to our bodies (as is the case with carrots).
4. Minimally processed food
Following the line of logic detailed above, the more processed a food item is, the lesser work our bodies have to do to break it down, thus the lower the thermic effect it has. As we might expect, heavily processed junk food, therefore, has a low thermic effect, compared to the natural whole food forms. However, interestingly, even the forms in which we buy our whole food items can dictate what their thermic effect might be.
Consider oats for instance—rolled oats, instant oats or oat flakes are flattened through steel drums to make them quicker to cook. This reduces the effort the body must put in order to digest it, bringing down the thermic effect. Steel-cut oats however are not processed this way so they have a higher thermic effect. Any process that makes it simpler for the body to digest will result in greater calorie absorption.
Ginger consumption also enhances the thermic effect of food while increasing satiety. Moreover, ginger increases thermogenesis, i.e. the heat production in the body from calorie burning and helps to rev up metabolism. In fact, one study found that dissolving 2 grams of ginger powder in hot water and consuming this along with the meal resulted in an additional 43 calories burnt than drinking hot water alone!
Several studies have found that certain spices such as chilli and mustard can also serve to increase thermogenesis. In chillies, the pungent principle known as Capsaicin is responsible for boosting fat-burning and increasing the feeling of fullness. A 2003 study in fact found that subjects who ate chilli pepper raised their metabolic rates for as long as 30 minutes after ingestion, whilst a 2010 study found that after one month of chilli supplementation, subjects burnt an extra 50 calories per day)!
7. Time of day
It is hypothesized that the thermic effect of food is higher in the morning than it is in the evening, explaining why eating heavier meals later at night might be widely associated with weight gain. Several studies support this idea and hypothesize that there may indeed be a daily variation in the thermic effect of food in line with our circadian rhythms. Try having your heavier meals earlier in the day! Not only does this mean a higher TEF, but may also help us sleep better as heavier meals before bed are thought to cause disturbances in sleep. Aim to have your last meal at least three hours before bed.
Do negative calorie foods exist?
You may have heard of the so-called “negative calorie foods”, which contain very few calories but still need the energy to digest. The hypothesis is that eating such foods would be “negative calorie” if the energy used in digestion (TEF) outweighs the calories contributed by the food itself. Foods hypothesized to fall into this category include celery, cabbage, lemons, lettuce, cucumbers or even chewing gum. Whilst this may sound like a miracle fat-burning hack, unfortunately, there is no evidence to support these claims.
For a food to be “negative calorie”, the thermic effect has to exceed 100%, which is far from reality. Take protein for instance, which only takes about 8% of its energy contact for digestion. If we really went to extremes and ate frozen celery, we might be able to tap into this effect, as our bodies would also have to consume energy to heat up the water content. However, even so, the effect would be minimal.
The effect of meal frequency on the thermic effect of food
We’ve all been told that we should eat several small meals a day to increase our metabolic rate. However, this too is a myth. Whilst digesting food does raise metabolism (due to the thermic effect of food), breaking meals down into smaller components holds no benefit. Eating four meals of 500 calories versus two meals of 1000 calories causes no difference. Rather, what you eat matters.
The widely-popularized notion of “starvation mode”, i.e. a reduction in metabolism when you don’t eat for a long period of time, is far from reality. Our bodies can not only fast for prolonged rates without any significant reduction in metabolism, but may thrive from doing so. It would take a very long fast indeed to trigger any significant reduction in metabolism.
What the experts say
Dr Robert Lustig, Professor Emeritus of Pediatrics in the Division of Endocrinology at the University of California, San Francisco, shares that “your boy is not a bomb calorimeter”. He states “different foodstuffs are metabolized at different rates. Turns out you have to invest energy to turn a protein into ATP (adenosine triphosphate, a form of energy used by cells), as opposed to say, a carbohydrate. So, you lose energy in the process, thus leading to net energy loss compared to carbohydrates. So,o from a calorie standpoint, if you measure it in a bomb calorimeter, they generate the same amount of heat, but that doesn’t have anything to do with biochemical ATP, or if it ends up raising your insulin and going into fat cells”.
All calories are not created equally. Whilst those aiming to lose weight may want to keep an eye on the total calories consumed, it is important to remember that our bodies are complex biochemical systems that don’t process all foods in the same way. Thus, eating calorically similar foods with different nutrient compositions will not have the same effect on the body; rather, each food will be unique in how much energy it takes for the body to digest.
This is where TEF comes into play, i.e. the amount of energy the body requires to break down different food groups. Staying mindful of this, we may want to increase the total TEF by opting for higher protein, minimally processed foods, especially if we are on a weight loss journey as protein takes the most energy to digest. Nevertheless, in the grand scheme of things, TEF only plays a very minor role and is not worth obsessing over, especially if it means losing out on nutrient-rich foods.
For lasting weight loss and weight loss maintenance, aim for a slow reduction in calories whilst choosing whole, minimally processed foods. Remember, TEF is just one piece of the puzzle!
Disclaimer: The contents of this article are for general information and educational purposes only. It neither provides any medical advice nor intends to substitute professional medical opinion on the treatment, diagnosis, prevention or alleviation of any disease, disorder or disability. Always consult with your doctor or qualified healthcare professional about your health condition and/or concerns before undertaking a new health care regimen including making any dietary or lifestyle changes.
- The Thermic Effect of Food: A Review
- Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet
- Ginger consumption enhances the thermic effect of food and promotes feelings of satiety without affecting metabolic and hormonal parameters in overweight men: A pilot study – PMC .
- Is It Bad to Eat Before Bed? – Cleveland Clinic.