But citing an increasing number of experiments done by other teams, Partridge said that some calories might count more than others. As part of the study, which was published today in online medical journal, PloS Biology, Partridge and colleagues tested two separate diets on a common type of fruit fly, known as drosophila. Some of the flies were given yeast, which is high in proteins and fat—a type of Zone diet for bugs. The others were fed sugar, a source of carbohydrates.
In each case, the flies were provided with fewer calories than normal. Reducing both nutrients led to longer lives, but restricting yeast increased a fly's life span by a further 60 percent compared to restricting sugar. Is it possible that a low-carb diet is bad for longevity?
"Mammals and flies are much different in that regard," said Partridge. Insects, unlike people, are not at risk for obesity and diabetes, meaning that they naturally benefit from sugary diets. At this point, Partridge said it is hard to tell what type of diet will keep us living longer. "The jury is still out," she said.
Eric Ravussin, PhD, of the Pennington Biomedical Research Center, who was not involved in the study, said that measuring calories in fruit flies is no easy task, which makes it hard to tell if specific foods can promote longer lives. Still, he has long been skeptical that all calories are the same. In looking at the problems associated with over eating, for example, "we know the origin of calories can be important," he said.
The recent findings, he added, could spur research that may find some foods are better than others, raising the hope for big eaters that life is worth living. But as one of the researchers involved in the NIA sponsored study on calorie restriction, Ravussin has watched an overwhelming majority of volunteers stick to a nutritiously balanced diet. Despite being asked to cut back on their calories by 10 to 30 percent, many have coped just fine. "I was surprised," said Ravussin.
