How Much Exercise Will It Take to Burn Off?

Yoni Freedhoff, MD


December 02, 2022

One of the least helpful but most pervasive misconceptions in weight management is that exercise is a primary driver of weight loss, which in turn leads to the unhealthy corollary that calories burned are the primary reason to exercise.

Yoni Freedhoff, MD

Perhaps it's consequent to that misperception that some have suggested that posting messages like how long you'd need to run to burn off this chocolate bar, known as physical activity calorie equivalents (PACEs), would be a good idea and would help to dissuade people from choosing high-calorie energy-dense foods.

Never mind that they might also teach people that the purpose and benefits of exercise are to burn calories so that they can eat junk food or that those who struggle with obesity struggle because they're too lazy to exercise enough.

Never mind as well that long-term studies looking at the association of large quantities of exercise on weight over time show that large quantities of it don't prevent weight gain but rather at best slow it down ever so slightly (Metcalf et al; Moholdt et al; May et al; Hankinson et al).

Never mind, too, that it's plausible that the reinforcement of the message that exercise is the driver of weight may lead those who fail to lose weight by way of exercise to stop exercising and, in so doing, miss out on the lengthy laundry list of exercises' dramatic benefits to health.

Okay but, never minding all of that, does it work? Does posting the distance needed to run off a chocolate bar lead people to eat fewer chocolate bars?

A recent study suggests that is does not. That study, "Evaluation of PACE Labels' Impact on Energy Purchased in Cafeterias: A Stepped-Wedge Randomised Controlled Trial," took place in 10 worksite cafeterias in England, which posted PACE labels on selected food and drinks. Purchases were measured during a baseline period without the PACE labels and again after their deployment. The study ran for 12 weeks, and over 250,000 transactions were recorded. The study's primary outcome was total calories purchased from PACE-labeled foods per day before and after their labeling. No effect was found.

That said, I'm not sure that the study was designed in a manner to find an effect. Looking at studies on the impact of calorie labeling in restaurants, some have concluded that they don't help. But when prepurchase attitudes around calories and weight management are explored, it's found that calorie labeling helps those who prior to their purchase identified themselves as people who were concerned about weight and the calorie content of their foods. It's just that there's not that many of them.

Perhaps the same could be true here — that those actively monitoring their diet in the name of weight or health did in fact change their behavior but that their numbers were too small to lead to any demonstrable overall effect.

As to why more people don't care?

Again, it's because there are immense multilayered degrees of privilege required to perpetually undertake intentional behavior in the name of health or weight, and no matter how badly we want there to be simple front-of-package nugget of information that will lead to population level consumption changes, interventions reliant on consciously made individual behavior changes are no match for life's many challenging realities. Worse, so long as we continue to expect information alone to change behaviors, we will also probably continue to perpetuate unhelpful weight bias, stereotypes, and misinformation.

Follow Yoni Freedhoff on Twitter: @YoniFreedhoff

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