Exercise: Energy In, Energy Out, Energy Sideways

Exercise for weight loss is a durable concept. Some advocates even push for food labels to describe the exercise necessary to burn calories in a food serving. But the premise for this is false. A new study in Current Biology explains the problem better than ever before. It turns out that when a person does extra exercise, their body compensates by burning less energy for other tasks.

The catchphrase that describes a simple formula of energy in and energy out is incomplete. Homeostasis is working in the background to take the net effect of exercise sideways. In fact, this research suggests that bodies with more adiposity tend to do even more to compensate for energy expended in exercise.

Let that sink in. With more body fat, exercise can have less effect on energy balance.

Burning Energy: Baseline and Exercise
Careau Infographic

Infographic by Clément Lanfranchi

This study by Vincent Careau and colleagues uses the largest dataset yet of energy expenditure measurements. These came from 1,784 persons in the International Atomic Energy Agency DLW database. Their data shows that the body offsets increases in energy used for physical activity with decreases in energy used for other things. On average, that offset is about 28 percent. So only 72 percent of the calories a person burns with exercise becomes extra calories burned for the day.

But the compensation is even greater for people with more body fat. At a higher fat mass, the body may compensate for up to 49 percent of the energy burned with exercise. Senior author John Speakman breaks it down for people who pay close attention to this:

“When your smart watch tells you that you burned 300 calories on your run it may be correct (probably isn’t). But even if it is correct, you should not be deluded into thinking you can now eat 300 calories more food.”

You Can’t Outrun a Bad Diet

This is just one more reason that you can’t outrun a bad diet. Exercise is great for physical health. But the popular concept that a person can simply work out to “burn off” excess fat is a lie that won’t die. If the goal is to reach and maintain a healthier weight, advice from a nutrition professional (an RDN) can be quite helpful.

Furthermore, this study is an important reminder that physiology is in control of a person’s energy balance and body composition. Each of us get to make some choices along the way, but our bodies get the final vote.

Click here for the study, here for a summary by the senior author, and here for further reporting on it.

Sideways, photograph © Kenny P. / flickr

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August 30, 2021

6 Responses to “Exercise: Energy In, Energy Out, Energy Sideways”

  1. August 30, 2021 at 8:01 am, Mary-Jo said:

    The great news about this research, which could be a bit of a consolation for those of us who live the bummer reality of exercising more, but not seeing our weight shift as much as we expect it should (!), is that improving diet has many more benefits than just effect on weight loss or maintenance — better cholesterol control, prevention of anemias, improved bone health, for example.

  2. August 30, 2021 at 8:55 am, Allen Browne said:

    Ted, well said – “ physiology is in control of a person’s energy balance and body composition. Each of us get to make some choices along the way, but our bodies get the final vote.”


  3. August 30, 2021 at 3:57 pm, Bruce Daggy said:

    I learned years ago from a colleague involved in setting physical activity guidelines that those estimates of energy expenditure on fitness equipment include basal metabolic rate (BMR). Whether that was due to good marketing (“Wow! Look at all the calories you just burned!”), or just some programmer borrowing numbers from calorie expenditure tables without contemplating how the end user would think about it, I know not. So, if someone thinks you can “earn” the right to consume 300 calories if it accurately says you just burned 300 calories, that’s never been correct. The figures would be more accurate in terms of physical activity calories burned for more intense exercise, since BMR would represent a smaller fraction of the total. But what’s really needed is some resistance exercise in the mix, 2-3 non-consecutive days per week, 20 minutes per day — as an adjunct to dietary changes. Studies have shown that a relatively small dose of resistance exercise helps maintain lean body mass, which in turn maintains a higher BMR. Make diet the focus for weight loss, but physical activity can provide a boost — especially with the focus on body composition, not just weight.

    • August 30, 2021 at 5:17 pm, Ted said:

      Good perspective, Bruce. Thank you.

  4. September 01, 2021 at 2:25 am, Patrick Handcock said:

    Just to get this straight, somehow that quote got messed with:

    — “physiology is in control of a person’s energy balance and body composition. Each of us sort of get to make some choices along the way, but the food and beverage, fossil-fuel, entertainment and other multinational corporations get the final vote.”

    • September 01, 2021 at 4:26 am, Ted said:

      I think the quote you have in mind is from Joseph Heller in Catch-22:

      “Just because you’re paranoid doesn’t mean they aren’t after you.”