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"That plateau is really different than the standard way of thinking about energy expenditure," Pontzer said. "What the World Health Organization and the people who build the Fitbit would tell you is that the more active you are, the more calories you burn per day. Period, full stop."
Based on the research, Pontzer has proposed a new model that upends the old "calories in, calories out" approach to exercise, where the body burns more calories with more physical activity in a linear relationship (also known as the "additive" model of energy expenditure).
He calls this the "constrained model" of energy expenditure, which shows that the effect of more physical activity on the human body is not linear. In light of our evolutionary history — when food sources were less reliable — he argues that the body sets a limit on how much energy it is willing to expend, regardless of how active we are.
"The overarching idea," Pontzer explained, "is that the body is trying to defend a particular energy expenditure level no matter how active you get."
This is still just a hypothesis. Pontzer and others will need to gather more evidence to validate it, and reconcile contradictory evidence showing that people can burn more energy as they add physical activity. So for now it's a fascinating possibility, among all the others, that may help explain why joining a gym as a sole strategy to lose weight is often an exercise in futility.
9) The government and the food industry are doling out unscientific advice
Since 1980, the obesity prevalence has doubled worldwide, with about 13 percent of the global population now registering as obese, according to the WHO. In the United States, nearly 70 percent of the population is either overweight or obese.
A lack of exercise and too many calories have been depicted as equal causes of the crisis. But as researchers put it in an article in BMJ, "You cannot outrun a bad diet."
Since at least the 1950s, Americans have been told that we can. This Public Health Reports paper outlines the dozens of government departments and organizations — from the American Heart Association to the US Department of Agriculture — whose campaigns suggested more physical activity (alone or in addition to diet) to reverse weight gain.
Unfortunately, we are losing the obesity battle because we are eating more than ever. But the exercise myth is still regularly deployed by the food and beverage industry — which are increasingly under fire for selling us too many unhealthy products.
"Physical activity is vital to the health and well-being of consumers," Coca-Cola says. The company has been aligning itself with exercise since the 1920s, and was recently exposed by the New York Times for funding obesity researchers who emphasize a lack of physical activity as the cause of the epidemic.
Coca-Cola is just one of many food companies that are encouraging us to get more exercise (and keep buying their products while we're at it): PepsiCo, Cargill, and Mondelez have all emphasized physical activity as a cause of obesity.
The exercise myth for weight loss also still appears in high-profile initiatives, like the former first lady Michelle Obama's Let's Move campaign — largely because of the food industry's lobbying efforts, according to Marion Nestle, a New York University nutrition professor. The White House's exercise focus to end childhood obesity, Nestle said, was "a strategic decision to make the message positive and doable and, at the same time, keep the food industry off its back."
But this focus on calories out, or the calories we can potentially burn in exercise, is "an inadequate and a potentially dangerous approach, because it is liable to encourage people to ignore or underestimate the greater impact of energy-in," an obesity doctor and professor wrote in the journal Public Health Nutrition.
In other words, we can lose sight of the fact that it's mostly too much food that's making us fat.
"There are all kinds of reasons to exercise that are good for your health," says Diana Thomas, a Montclair State University obesity researcher. "However, if you're trying to lose weight, the biggest problem I see is food. We need to cut back the food we're eating."
The evidence is now clear: Exercise is excellent for health, but it's not important for weight loss. The two things should never be given equal weight in the obesity debate.
10) So what actually works for weight loss?
At the individual level, some very good research on what works for weight loss comes from the National Weight Control Registry, a study that has parsed the traits, habits, and behaviors of adults who have lost at least 30 pounds and kept it off for a minimum of one year. They currently have more than 10,000 members enrolled in the study, and these folks respond to annual questionnaires about how they've managed to keep their weight down.
The researchers behind the study found that people who have had success losing weight have a few things in common: They weigh themselves at least once a week. They restrict their calorie intake, stay away from high-fat foods, and watch their portion sizes. They also exercise regularly.
But note: These folks use physical activity in addition to calorie counting and other behavioral changes. Every reliable expert I've ever spoken to on weight loss says the most important thing a person can do is limit calories in a way they like and can sustain, and focus on eating healthfully.
In general, diet with exercise can work better than calorie cutting alone, but with only marginal additional weight loss benefits. Consider this chart from a randomized trial that was done on a group of overweight folks: The group that restricted calories lost about the same amount of weight as the group that dieted and exercised, though the exercisers didn't cut as many calories:
If you embark on a weight loss journey that involves both adding exercise and cutting calories, Montclair's Thomas warned not to count those calories burned in physical activity toward extra eating.
"Pretend you didn't exercise at all," she said. "You will most likely compensate anyway, so think of exercising just for health improvement but not for weight loss."