Can You Lose Weight with Exercise Alone?

Don’t stress too much about cutting calories if you want to shed pounds—focus on getting more exercise. That’s the controversial message beverage giant Coca-Cola is backing in its new campaign to curb obesity. Coke is pushing this idea via a new Coke-backed nonprofit called Global Energy Balance Network, The New York Times reported on August 9. Money from Coke, the Times reported, is also financing studies that support the notion that exercise trumps diet. But is there any merit to such a stance? Not much, says Rutgers University–based diet and behavior expert Charlotte Markey. She is the author of an upcoming cover story in Scientific American MIND on this topic, and spoke about the Coke claims with Scientific American on Monday.
[An edited transcript of the interview follows.]
In your fall Scientific American MIND feature you write “study after study shows that working out is not terribly effective for weight loss on its own.” Why is that?
Exercise increases appetite, and most people just make up for whatever they exercised off. There’s a lot of wonderful reasons to exercise and I always suggest it to people who are trying to lose weight—some sort of exercise regimen keeps them focused on their health and doing what is good for them, and it’s psychologically healthy. But in and of itself it won’t usually help people lose weight. 
Two years ago there was a review study in Frontiers in Psychology that concluded dieting often actually led to weight gain. Why would that happen?
When people try to diet, they try to restrict themselves, which often leads to overeating. They cut out food groups which make those food groups more desirable to them. They think too much about short-term goals and don’t think about sustainable changes. But if you are going to lose weight, you have to change your behaviors for the rest of your life or otherwise you gain it back. That’s not a sexy message because it seems daunting. 
Coke’s message is don’t worry so much about dieting but worry a bit more about exercise. Is there something to that then?
I find everything going on here very troubling. In the promotional video from Coke’s group, linked to by the NYT, exercise scientist Steve Blair says we don’t know what is causing obesity and we need more research. That message is oversimplified and terribly misleading. We actually know a great deal about what leads to obesity. It’s not a great mystery. People are eating too much and not exercising enough…that makes it inevitable that people will be obese. The group’s emphasis on physical activity is misleading based on what the data shows. There’s no data to support saying if you exercise for 30 minutes three times a week that this will take care of the problem. We have data refuting that. 
In reality, we need people to stop drinking sugary beverages like soda. Soda is the one consumable beverage that is repeatedly cited as having the biggest impact on obesity rates. From a public health standpoint, we want soda out of schools and we want cities to really decrease intake of soda—and Coca-Cola knows this and knows they are being proactive and defensive against taxes on soda and other limitations.
What does a sustainable weight loss regime look like?
It looks like making regular, sustainable dietary changes. It does not have to be a complete revamp of someone’s way of eating since that is not typically sustainable. But, in most cases, it has to involve dropping 300 or more calories per day; that can be done by dropping a couple sodas per day. People have to commit to this and prepare themselves—weight loss is a marathon and not a sprint. 
Exercise is important for sustaining weight loss though, right? Can you talk a bit about what the literature says on that?
Exercise makes people feel good. Avoiding food can just make people feel deprived. Exercise also gets people distracted from wanting food or other stressors, and it alleviates stress. 
But exercise also has real physical benefits.
Right. We are burning calories. It’s good for all of our systems—from our heart to our digestive system to our psychological well-being. People should exercise for their health overall but alone it’s not good for weight loss. 
Researchers are supposed to note their funding sources. So if scientists acknowledge their work is supported by Coke, does it resolve conflicts of interest?
I think that’s a good ethical question. Funding research is expensive. If Coke or anyone wants to contribute to unbiased research, then I don’t want to stop them. I don’t think that’s inherently a bad thing. Obviously there is a conflict of interest, and I don’t think it’s an accident that Coke seems to be targeting people who have been doing physical activity work their entire careers and not people who have been doing eating and diet work. I am not arguing that exercise isn’t important but it strikes me as a bit suspect. No respectable researcher would be part of an enterprise that hides results that do not support the Coke message, and some of these researchers are well known and quite reputable so I do not think that is on the table. 
I think the issue is what is done with the results and how they are presented to the public. Coke is spending millions of dollars here and has a marketing PR budget that researchers don’t have so they can take the findings and share them and use them to try to fight policy and all these laws that are being debated about taxing soda. Coke has this body of evidence that is biased since they are funding exercise studies and not diet studies. They can then use these in public policy debates, and I think that could be really worrisome.

[Editor’s Note: Scientific American asked Coca-Cola to explain their position and the company e-mailed this response: “We recognize moderation and diet play a pivotal role in managing health and weight in combination with exercise. In fact, we continue to take steps to help people manage their calories—whether it’s through the introduction of smaller-sized packs, front-of-pack calorie labeling or innovation through new products such as Coca-Cola Life. In addition, last year we joined with the American Beverage Association, the Alliance for a Healthier Generation and other industry partners on a beverage-calorie reduction commitment for every person of 20 percent by 2025. Clearly, we support calorie reduction as a tool for a healthier life.”]