How to Calculate the Thermic Effect of Food

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If you've ever tried losing weight, you're probably familiar with the concept of counting calories. In addition to the calories we eat and those we burn through exercise, our bodies also expend energy through daily activities like breathing, blinking, sleeping, and even digesting food.

What Is the Thermic Effect of Food?

The thermic effect of food (TEF) is one of the many ways our bodies use energy throughout the day. Along with the TEF, there's also a thermic effect of exercise and our basal metabolic rate. In addition, we burn calories through the little movements we do (such as fidgeting), referred to as non-exercise activity thermogenesis (NEAT). All of these make up our total energy expenditure.

After eating, our energy expenditure increases for a period of time as our bodies work to break down the food we eat into nutrients that we can store or use. This thermic effect of food generally makes up about 10% of our total energy expenditure. The exact TEF varies from person to person and depends on the macronutrient composition of our meal and other characteristics.

How to Measure TEF

TEF is an estimation produced in a science lab, because TEF can only be calculated under controlled conditions. The gold standard for measuring TEF involves comparing calories burned in the fed versus fasting state. Newer methods are being studied, such as using a metabolic chamber to look at energy expenditure during physical activity after eating.

There isn't a reliable way to know the exact TEF of a given meal at home. While certain foods are believed to have a higher TEF than others, it's impossible to do a specific calculation outside of the lab.

Do "Negative-Calorie Foods" Exist?

A widespread dietary myth about the concept of negative-calorie foods has left many people confused about TEF. Vegetables that are high in water and fiber (like celery, lettuce, and cucumbers) are sometimes thought to burn more calories during digestion than they actually contain. The theory goes that eating these foods leads to a net loss of calories.

However, negative-calorie foods do not exist. While low-calorie foods help support a healthy weight, trying to lose weight through TEF alone is not a sustainable or effective plan.

Factors That Influence TEF

There are several misconceptions about which factors affect TEF. For instance, some people believe that eating a large breakfast will increase their calorie burn throughout the day and lead to weight loss. However, studies on breakfast intake and body weight are largely inconclusive.

Certain spices and caffeine are associated with a minor uptick in TEF, but these "metabolism-boosting foods" aren't exactly the miracle calorie-burners they're often made out to be. Appetite regulation is complex, and the impact of these factors is typically negligible and short-lasting.

These physiological factors appear to have the greatest impact on TEF:

  • Age: TEF decreases with age even after adjusting for other contributing factors.
  • Insulin resistance: The presence of type 2 diabetes and obesity seem to reduce TEF, perhaps making weight loss more difficult as a result.
  • Physical activity level: In both younger and older adults, physical activity increases TEF. TEF is 31% to 45% higher in physically active individuals of various age groups compared to their sedentary counterparts.

Timing and Composition of Meals

When and what we eat also affects how much our bodies burn during digestion. Eating meals slowly and chewing more increases TEF. There is conflicting evidence on whether regularly scheduled meals, versus skipping meals, raises or reduces TEF.

Studies show a 10% higher TEF in meals that are considered high-protein versus low- or medium-protein meals. However, this effect is limited to the current meal and does not produce long-term changes in metabolism. Compared to high-carbohydrate or high-fat meals, high-protein meals have been associated with a 17% increase in TEF.

Certain types of dietary fat, including medium-chain triglycerides, also appear to raise TEF temporarily. Unprocessed foods that are higher in dietary fiber also require more energy to break down, boosting TEF compared to highly processed foods.

Total Energy Expenditure

The thought of burning calories while we eat may sound appealing, but it's important to keep the magnitude of TEF in perspective. Weight management relies more heavily on the types of foods we eat, our portion sizes, our body composition, and how active we are.

Instead of placing too much emphasis on the TEF of different foods, it's best to choose foods that give our bodies the fuel required to support an active lifestyle. Our daily activity level (through both structured and non-structured movement) has a major influence on how many calories we use. Just look at this general breakdown of a typical person's total energy expenditure:

  • Basal metabolic rate: 60%
  • Intentional exercise: 10%
  • NEAT: 20%
  • TEF: 10%

You can't do much to change your basal metabolic rate. But to boost your activity-related energy burn (including exercise and NEAT), use a pedometer to track your daily step count, switch your desk to a standing desk, or take the stairs instead of the elevator. All of these small changes can add up to a lifestyle that makes it easier to maintain a healthy weight.

A Word From Verywell

The number of calories our bodies use each day is influenced by a variety of factors, with TEF playing a minor role. Losing weight requires a bit of trial and error to find the right balance of calories that enables weight loss without feeling overly deprived.

Since everybody is different, there's no exact way to measure your total energy expenditure or TEF outside of a lab. Instead of focusing on the details, work on the big stuff first, like choosing nutritious foods, and upping your daily activity level.

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