Thermic effect of food, and why meal count doesn't change it

Key takeaways

• The thermic effect of food is the extra energy your body spends absorbing, processing and storing what you eat. On a mixed diet it comes to about 10 percent of the day's calories.¹
• Protein has the highest cost of the three macros, with reported values of 20 to 30 percent of its calories. Carbs sit at 5 to 10 percent and fat at 0 to 3 percent.¹
• Splitting the same food into more meals didn't raise the day's total. Studies that measured all 24 hours found no difference in burn between nibbling and gorging.²
• In a 2010 trial, 3 meals plus 3 snacks made no significant difference to body fat measures or appetite compared with 3 meals on the same calorie cut. A 2015 meta-analysis of 15 studies traced its positive result to a single study.³⁴
• How much you eat and how much of it is protein set the cost. Logged macros show your own mix for the day.¹

What is the thermic effect of food?

It's the rise in calorie burn that follows a meal, the energy used to absorb, process and store the food. A 2004 review put it at about 10 percent of the calories eaten in a day on a mixed diet, and found that the amount of food and its protein share set its size, while studies of meal frequency found no change in the 24 hour total.¹²

Researchers also call it diet-induced thermogenesis. It's measured as the increase above fasting resting burn, divided by the calories in the food, so it comes out as a percentage of what was eaten.¹

Westerterp's review gives a wider range too. A mixed diet eaten at energy balance spends 5 to 15 percent of daily burn on it, with higher values when protein and alcohol make up more of the diet and lower values when fat does.¹

Thermic effect of food by macronutrient

Read across each row. The last column applies the range to 500 calories of that nutrient alone.

At 500 calories of each, protein costs 100 to 150 calories to process and fat costs 0 to 15. In the review's words, the thermic effect of alcohol is similar to that of protein.¹

How long does the thermic effect of food last?

Hours. In a respiration chamber study of 17 women and 20 men, cited in the 2004 review, resting burn hadn't fallen back to its fasting level 4 hours after breakfast, when lunch was served, or 5 hours after lunch, when dinner was served. Overnight it got back to the fasting level about 8 hours after dinner.¹

So on an ordinary day of meals, the rise from one meal was still going when the next meal started.¹

Does meal frequency change the thermic effect of food?

Not over a whole day. Bellisle, McDevitt and Prentice reviewed the meal frequency research in 1997. Short tests where one load of food was split into several small meals pointed both ways. Some found a higher thermic effect, others found the opposite, and most found no difference.²

The stronger evidence came from studies that measured the full 24 hours, with whole-body calorimetry or doubly labeled water. They found no difference in total energy burned between nibbling and gorging.²

A 2019 review of the thermic effect read the per meal studies differently, listing larger meals as raising it compared with frequent small ones. It also said the effects of meal timing still need to be clarified. Neither finding changes the 24 hour totals Bellisle's review described.⁵²

Does eating more often boost metabolism?

The studies don't support it. The idea grew from surveys in which people who reported eating more often tended to weigh less. Bellisle's review found that many studies saw no link at all, and the ones that did were open to under-reporting of food and to people changing how they ate after gaining weight. The authors called the survey evidence at best very weak.²

Cameron's 2010 trial tested meal frequency during a calorie cut. Sixteen adults with obesity, 8 women and 8 men, followed the same calorie restriction of 2,931 kilojoules a day, about 700 calories, for 8 weeks. One group ate 3 meals a day and the other ate 3 meals plus 3 snacks. The groups showed no significant differences in body fat measures, appetite ratings, or the gut hormones ghrelin and peptide YY.³

Schoenfeld, Aragon and Krieger pooled 15 meal frequency studies in 2015. More frequent meals first looked linked to more fat loss and more fat-free mass. When they reran the analysis leaving studies out, the positive result came from a single study, and they said the finding should be read with caution.⁴

Bellisle's review also found that, with one exception, meal frequency didn't change weight loss on reduced calorie diets. It concluded that any effect of meal pattern on body weight probably works through how much people eat, not through how many calories they burn.²

Does meal timing change the thermic effect of food?

The time of day didn't matter in the test the 2004 review cites. Weststrate's team repeated the measurements at different times of day and found no significant daily rhythm in the thermic effect.¹

The research on time of day is thin, though. The 2019 review lists meal timing among the factors whose effects are still unclear.⁵

What does change the thermic effect of food?

Two things, according to the 2004 review. The main one is the energy content of the food, and the next is the protein fraction. Alcohol raises it as well.¹

One 24 hour respiration chamber study in the review fed 8 people the same calories two ways. With 10 percent of energy from protein and 60 percent from fat, the thermic effect was 10.5 percent of intake. With 30 percent from protein and 10 percent from fat, it was 14.6 percent.¹

Since the cost is a share of the food, a smaller day of eating has a smaller thermic effect in calories and a bigger day has a bigger one. It moves with the food you eat rather than adding anything on its own.¹

Why do thermic effect numbers vary so much?

Partly from how it's measured. Most studies in the 2004 review measured burn under a ventilated hood for 4 to 5.5 hours after a test meal and reported values below 10 percent of the meal's calories. Studies that measured a full 24 hours in a respiration chamber came out higher, and once adjusted to the same baseline they were close to 10 percent.¹

It also varies within the same person. Repeat tests in the same people differed by 6 to 30 percent with a hood and by 43 to 48 percent in a chamber, the review reports. One test after one meal is a rough reading.¹

How to see your own macro mix

• Log everything you eat and drink for a few typical days, including oils, sauces and snacks.
• Look at the share of the day's calories from protein, carbs and fat, for the whole day rather than meal by meal.
• Run your own day through the ranges in the table, the way the worked example does.
• Don't add the thermic effect on top of your daily burn. It's already one of the three parts of daily energy expenditure, along with resting burn and activity.¹
• With TrueCal Pro, a typed meal description becomes a food log with calories and macros, so the day's protein, carbs and fat are added up for you.

Common myths

• Myth, six small meals keep your metabolism running all day. In 24 hour measurements, total burn was the same whether people nibbled or ate fewer, larger meals.²
• Myth, snacking between meals speeds up weight loss. In the 2010 trial, adding 3 snacks to 3 meals on the same calorie restriction made no significant difference to body fat measures.³
• Myth, high protein food burns itself off. Protein uses 20 to 30 percent of its own calories in processing, so most of its calories are still there.¹

A note on medical advice

This article is for general information and isn't medical advice. Talk with your clinician about your own situation.

Worked example

Take a 2,000 calorie day and use the middle of each published range, 25 percent for protein, 7.5 percent for carbs and 1.5 percent for fat. If 15 percent of the calories come from protein, 50 percent from carbs and 35 percent from fat, that's 300, 1,000 and 700 calories. Processing them costs about 75, 75 and 10.5 calories, about 160 in all. Shift the same 2,000 calories to 30 percent protein, 40 percent carbs and 30 percent fat, which is 600, 800 and 600 calories, and the cost is about 150, 60 and 9, about 219. Both days sit near the 10 percent the 2004 review gives for a mixed diet, which is 200 calories here. Eating either day as 3 meals or as 6 leaves its total where it was, which is what the 24 hour studies found. These are rough estimates from the ranges, not a measurement of anyone's body.¹²

A closer look

Per meal studies disagree on meal size. A 2019 review lists larger meals as raising the thermic effect, while the short tests in Bellisle's 1997 review pointed both ways and mostly found no difference. The studies in that 1997 review that measured all 24 hours, by whole-body calorimetry or doubly labeled water, found no difference in total burn between eating many small meals and a few large ones.⁵²

Questions and answers

Related guides

• How to track calories
• Do foods that boost metabolism work?
• What is TDEE?
• How to count macros
• How much protein to lose weight
• Is starvation mode real?
• The slow metabolism myth

Sources

1. Nutrition and Metabolism. Westerterp. 2004.
2. British Journal of Nutrition. Bellisle, McDevitt, Prentice. 1997.
3. British Journal of Nutrition. Cameron, Cyr, Doucet. 2010.
4. Nutrition Reviews. Schoenfeld, Aragon, Krieger. 2015.
5. Journal of the American College of Nutrition. Calcagno. 2019.