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Calories in Food

Calories in Food

Rumor: You Can Burn Calories without Lifting a Finger

Do low-carb diets really burn more calories?

When 21 overweight or obese young adults followed a very-low-carbohydrate diet for one month, they burned more than 300 additional calories a day than when they followed a low-fat diet for a month, reported the Los Angeles Times and other news media in 2012.

“That’s roughly equal to an hour of moderate physical activity—without lifting a finger,” David Ludwig, director of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital and the lead researcher on the study told the newspaper.

Here’s what got lost in some of the news reports:

Adverse effects. The very-low-carb diet (which was higher in protein and fat) raised c-reactive protein (a marker of inflammation), cortisol (a marker of stress), and non-HDL (“bad”) cholesterol.

More calorie burning? A much longer (two-year) study on 811 people found no difference in calorie burning on higher- vs. lower-carb diets (though none were very low).

Long-term studies. Most importantly, three studies that lasted one or two years have tested low-fat versus low-carb diets on a total of more than 1,200 people. The results: no difference in long-term weight loss or regain. Period.

“In the studies that were one or two years long, a very-low-carb diet led to no more weight loss than other diets,” says Frank Sacks, professor of cardiovascular disease prevention at the Harvard School of Public Health, who ran the largest two-year diet study.

If, as Ludwig’s study reported, people burned more calories on the low-carb diet, adds Sacks, “it’s odd that body weight was exactly the same after 30 days.”

The Real Story: The best long-term studies show that people lose—and keep off—as much weight on high-carb diets as they do on low-carb diets.

Sources: JAMA 307: 2627, 2012. Obesity 2012. DOI:10.1038/oby.2012.127. N. Engl. J. Med. 360: 859, 2009. Ann. Intern. Med. 153: 147, 2010. JAMA 293: 43, 2005.

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