You may not have noticed it yet, but sodamakers are working hard to get you off your couch. On Aug. 9, a New York Times article revealed that Coca-Cola was quietly funding a group of scientists called Global Energy Balance Network that emphasizes the role of exercise, as opposed to diet, in fighting obesity. There’s also Mixify, an advertising and social-media campaign launched by Coca-Cola, Dr Pepper, Pepsi and the American Beverage Association that suggests “mixing lazy days with something light, following sweaty workouts with whatever you’re craving”–encouraging the idea that when you’re active, you can afford to eat or drink whatever you like.
This has some nutrition and obesity experts charging soda companies, whose sales of carbonated soft drinks have hit a 20-year low, with cherry-picking science to make its products more appealing. “The notion that we can exercise away a bad diet is absolutely unfounded,” says Dr. David Ludwig, director of the Obesity Prevention Center at Boston Children’s Hospital and professor of pediatrics and nutrition at Harvard, “and it’s contradicted by many research studies.” Indeed, there isn’t strong evidence to show that exercise alone–at least at the level that anyone other than a marathoner maintains–can help people shed pounds and keep them off.
And the American public seems to know this too. After rising sharply in recent decades, obesity rates are stabilizing, thanks in large part to a lightening up of the diet. Faced with pressure from health experts, Americans are curbing their calories–including from soda–for the first time in 40 years.
In response, some soda manufacturers have made changes in an attempt to make their products healthier, including moving away from some controversial artificial sweeteners in their diet products. For their sugared versions, however, they’re focusing on the old “calories in, calories out” equation. The problem, say experts, is that people are notoriously bad at measuring both what they eat and what they burn–and, even more significantly, our bodies don’t treat all calories the same way, especially when they are exposed to a lot of sweets over time. Like a car that’s repeatedly driven at high speed and then suddenly halted, humans’ biological metabolic brakes–in this case the insulin that processes sugar–start to wear down and become less efficient. That’s the first step toward weight gain and Type 2 diabetes. The more processed and refined foods are eaten, the more insulin is pumped out to break down the food. And the more insulin that circulates around, the more fat is sequestered away, making it extremely difficult to lose weight.
That’s why the idea of just working off the calories you eat doesn’t capture all the hormonal and metabolic changes that occur in the body when food comes in. “If you’re a toaster oven, then the calorie-balance model is for you,” says Ludwig. “If you’re a human, it’s not helpful.”
It’s not the first time science has been used to sway public perceptions about the health effects of certain behaviors; the tobacco industry famously promoted messaging based on studies that claimed to prove that “light” or “low-tar” cigarettes were less harmful than regular ones.
No doctor or public-health official would argue with the soundness of getting more exercise, but in these new campaigns, scientifically solid advice is being invoked to encourage the less scientifically valid idea that extra calories from processed foods or sugared drinks can be easily worked off. “It’s tough to argue with ‘exercise is good for you,'” says Dr. Yoni Freedhoff of the University of Ottawa, who tipped off the Times to Coca-Cola’s financial ties to those scientists. “But Coca-Cola is getting involved in a way that isn’t in the best interest of public health.”
When asked for comment, a Coca-Cola representative directed TIME to a statement on its website that noted “a balanced diet and regular exercise are two key ingredients for a healthy lifestyle and that is reflected in both our long-term and short-term business actions.”
This appears in the August 24, 2015 issue of TIME.