Smithsonian.com

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A new Harvard study challenges the traditional understanding of calories, postulating that it’s all about quality and not quantity. For those looking to lose weight, the source of those calories is more influential than the sheer number.

ABC News reports on the results:

The kind of calories the body gets may affect how efficiently people burn their body’s energy, which can be key for losing weight and keeping it off.

The researchers studied 21 overweight and obese adults. First, they pushed them to each lose 12.5 percent of their body weight, then they compared three different diets—low-fat, the Atkin’s Diet and the low-glycemic index plan—to see which was most effective at maintaining that weight.

The results weren’t good news for low-fat diet aficionados. When dieters followed that plan, their bodies burned fewer calories than when they were following the low-carb or low-glycemic index diets. And the low-fat diet changed certain metabolic factors in their bodies that typically predicted weight regain.

The low-carb diet seemed to help participants burn the most calories. But it also increased certain markers of stress and inflammation in the body, such as the stress hormone cortisol, which are risk factors for cardiovascular disease and other health problems.

In the end, the researchers found that the low-glycemic index diet struck the right balance for the participants. It helped the dieters burn more calories, though not as many as the low-carb diet, but didn’t seem to increase disease-causing stress markers in the body.