Life / Health

Sex doesn't burn as many calories as you think

Sex burns hundreds of calories. Breastfeeding an infant can prevent obesity later in life. And skipping breakfast regularly can lead to excessive weight gain.

Those are a few of the obesity-related myths debunked in a study published Thursday in the New England Journal of Medicine.

The researchers are trying to put to rest misleading — or flat-out wrong — medical information that’s often spread by media and can impact policy decisions.

“It’s a call to skepticism, it’s a call to empiricism,” said lead author David Allison, director of the Nutrition Obesity Research Center at the University of Birmingham at Alabama.

“A call to science to get in the habit of asking questions such as ‘How do you know that? How would someone know that?’”

The study goes after the popular belief that sex can shed between 100 and 300 calories. Indeed, one article on WebMD, a popular medical reference website, suggests 30 minutes of coitus can erase 85 calories.

But the study authors found that for men, the calorie-reducing effects of lovemaking are equivalent to a walk of about 4 km per hour, or a burn of roughly 21 calories.

The authors also dissected the so-called 3,500 Calorie Rule, which holds that eating an extra 3,500 calories will result in a one-pound weight gain. That’s faulty reasoning, said Arya Sharma, chair in obesity research and management at the University of Alberta. The body, he said, is constantly adapting to caloric changes.

“You can’t simply add those calories up and assume that it’s going to be weight gain or weight loss,” said Sharma, who was not involved in the study. “The paper reminds us … that some of the things we assume about obesity are not supported by the evidence.”

Allison and his co-authors also take on the presumption that eating a regular breakfast can stave off obesity, the suggestion being that skipping an early-morning meal fuels overeating later in the day. But that hasn’t been proven, Allison said.

And so is the long-held belief breastfeeding prevents obesity. The paper references randomized, controlled tests — included one 6-year study of 13,000 children published in 2008 — that offer “no compelling evidence of an effect of breastfeeding on obesity.”

The study was funded by the U.S. National Institutes of Health. Several authors have professional affiliations with food and drug companies, including the Coca-Cola Foundation, Kraft Foods and the diet program Jenny Craig.

More on