If you're overweight and hoping to shed pounds, but still regularly indulging in french fries — don't count on exercise to salvage your weight-loss efforts. To truly slim down, obese and overweight people need to watch what they eat and get moving, according to a new analysis of weight-loss trials dating back to 1985.
"Exercise by itself is not going to be an effective weight-loss strategy for an individual, you really need to combine exercise with better nutrition," said lead study author Dr. Kelly Shaw.
Shaw is a public health physician with the Department of Health and Human Services in Tasmania, Australia. She was surprised by the amount of weight loss achievable through diet alone, compared to exercise. "I thought that exercise would result in greater weight loss than it did as a stand-alone intervention," she said.
"If you are a reductionist and came to me and said, 'Look I want to lose weight and I'm prepared to diet or exercise, but not both, what should I do?' My response would be, you need to look at your nutritional intake because there's a bigger bang for your buck from modifying nutrition than there is with physical activity," Shaw said.
The review of 43 trials appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.
"The literature is pretty clear that, in the short run, diet is way more important than activity for weight loss," said John Jakicic, a health researcher who was not involved in the Cochrane review. "One candy bar can completely wipe out a bout of exercise," Jakicic said.
"Within six months, with diet alone we can get about a 9 or 10 kilogram weight loss, which is over 20 pounds, versus with activity we get about a 2 kilogram weight loss in that same period of time," said Jakicic, chair of the department of Health and Physical Activity at the University of Pittsburgh School of Education.
But don't discount the benefits of exercise. "Diet is very important to get weight off. But exercise seems to be one of those key factors for keeping the weight off when you lose it," Jakicic said.
"From a population level, I think that means that our good nutrition programs and our healthy physical activity programs really have to be very well-integrated," Shaw said.
But Jakicic said that integration is rare in the United States where gym-based programs often focus on exercise, while programs like Weight Watchers and Jenny Craig focus mainly on food.
"Those folks who only focus on diet and don't worry about the activity are really short-changing themselves," Jakicic said.
The Cochrane review uncovered independent benefits from exercise that boost heart health and lower the risks for cardiovascular disease. "If your main goal is health and well-being, then exercise offers you significant improvements in your blood pressure, lipids and your blood sugar," Shaw said.
"The meta-analysis tells us what the individual needs to do to improve body weight, to improve cardiovascular disease risk," Shaw said. The challenge now, she added, is for policy-makers and governments "to look at ways that we can encourage behaviors in our population that encourage people to get exercise back into their lives, and to eat a diet that is less energy-dense and more nutritionally sound."
Shaw points to other successful public health campaigns — like the tobacco control effort — and believes communities can take a similar socio-environmental approach in the "eat right, get moving" campaign.
Shaw said past public health campaigns prove that legislative and legal levers work to change behavior. Other possible strategies include fiscal incentives, perhaps subsidies for fresh fruit and vegetables, or even smart urban planning that eschews fast-food restaurants and builds in walking trails and green spaces, she said.