Nutritional Pearls: License To Eat

Margret is a 27-year-old woman currently trying to lose weight. She tells you that exercise makes her hungry, and the harder she works out, the more food she allows herself to eat afterward. She explains that her wearable fitness tracker will allot her more calories after a hard workout, which she often takes advantage of.

How would you advise your patient?
(Answer and discussion on next page)

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Answer: Exercise is not an excuse to eat more.

There are 2 problems here: First, research shows that exercise actually reduces appetite for up to 30 minutes or more after exercise, and second, we also know that wearable activity trackers vary in their accuracy.

Exercise is important for weight loss as well as weight management, to say nothing of its other health benefits. Yet many of my patients focus on its ability to burn calories, a viewpoint encouraged by many online diet and weight-loss trackers, including those associated with wearable activity trackers. These will actually take into account the estimated number of calories burned through exercise when calculating allotted calorie intake for the day.

The Research

A team in Bristol in the United Kingdom decided to investigate the interaction between burning calories, subsequent hunger, and how much people chose to eat in response to that hunger. Seventy healthy adult men and women were recruited to participate in an exercise study in which they were asked to ride on a stationary cycle for about 15 minutes at a mild to moderate intensity of between 60 and 90 revolutions per minute. Each participant was directed to ride until the researcher told them to stop, which was calculated individually so that each participant burned about 120 calories. The appetite and mood questionnaires were repeated immediately after the exercise and then again after the participant had rested for about 10 minutes. Finally, they were offered a snack of orange juice, tortilla chips, and chocolate chip cookies.

Although each participant actually burned about the same number of calories (120), half the participants were informed that they had burned about 50 calories, and the other half were informed that they had burned about 260 calories. The question was, given that information, would the subjects feel more or less hungry, and would they eat more of less of the snacks?

The Results

All of the participants reported about the same levels of hunger before beginning the exercise (likely because they'd been asked to refrain from consuming calorie-containing items for 3 hours prior to entering the lab). Those who were told that they had burned only 50 calories reported feeling about 65% as hungry as they were before the exercise, while those who were informed that they had burned 265 calories reported feeling about 55% as hungry—which the authors describe as not significant. That said, those who believed that they had burned more calories still ate more than those who believed they had burned fewer calories—in fact, they consumed, on average, 92 more calories of the snacks, of which 67 of those calories were in the form of chocolate chip cookies.

What’s the “Take-Home”?

It's clear that the brain can override the body's appetite: The authors of this study called the effect "license to eat." Tell your patients to take their trackers’ information about number of calories burned with a grain of salt, and that they should remember that exercise is not an excuse to eat more, whether it's chocolate chip cookies or some other tempting morsel.

Reference:
McCaig DC, Hawkins LA, Rogers PJ. Licence to eat: information on energy expended during exercise affects subsequent energy intake. Appetite. 2016;107:323-329.