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.