Study shows obese flies live longer on diet, at all ages

Obese old flies become healthier and live longer if they follow a diet, researchers at the University of Connecticut reported December 8. PNAS. If this effect holds true in humans, it would mean that it is never too late for obese people to improve their health through diet.

For many of us, overeating goes hand in hand with aging and a tendency toward obesity. Different health organizations define obesity differently, but all agree that it means excess body fat and is associated with a host of metabolism-related diseases, including heart disease and diabetes.

Numerous animal studies have shown that eating less, that is, severely limiting calories without malnutrition, extends lifespan. While human trials have shown beneficial health effects of reduced diet, particularly in healthy obese people, studies examining lifespan effects have proven unrealistic for humans.

Now, researchers at the UConn School of Medicine have shown that fruit flies fed a high-sugar, high-protein, high-calorie diet that mimics the processed modern diet exhibited metabolic changes similar to those in obese humans. Switching these obese flies to a low-calorie diet, even very late in life, can dramatically change their metabolism and prolong their lives.

Fruit flies live short and fast: the lifespan of flies raised on a high-calorie diet is less than 80 days, while those that live the longest on a low-calorie diet can reach 120 days. To test whether changes in diet late in life can alter a fly’s lifespan, researchers led by geneticist Blanka Rogina of UConn’s Department of Genetics and Genome Sciences and the Genomics Institute systems reared multiple batches of fruit flies.

Some flies were raised on a low-calorie diet that provided only half the energy of a normal diet, while the others were raised on a high-calorie diet that provided three times the usual number of calories.

In this study, they looked specifically at male flies. The young flies switched from a high-calorie diet to a low-calorie diet at 20 days old and lived a very long time, similar to flies fed a low-calorie diet from day one.

What surprised the researchers was that switching to a low-calorie diet remained a reliable way to extend lifespan, even for old, unhealthy flies. Older insects raised on a high-calorie diet had more lipids in their bodies and spent more energy defending their bodies against reactive oxygen species.

Their mortality rate was also higher than that of flies raised on a low-calorie diet. But when the surviving high-calorie flies were switched to a low-calorie diet after 50 or even 60 days (when most of the high-calorie flies were already dead), their metabolism changed, their mortality rate dropped, and their lifespan life has lengthened.

“Our studies were performed on aged flies on a high-calorie diet, similar to obese individuals, suggesting that a late-life diet change in obese humans could have a remarkable beneficial impact on health “, explains Rogina.

UConn School of Medicine Genetics and Genome Sciences President Brent Graveley and other researchers on the team looked at the genes expressed by the high-calorie flies and compared them to the low-calorie flies. The genes that control physiological and metabolic adaptation are different between groups.

“The remarkable finding of this study is that even after living a significant portion of their lives on a high-calorie diet, flies can experience the benefits of extended lifespan by simply switching to a low-calorie diet,” Graveley explains.

The team’s results show that flies’ metabolism can adapt to a change in diet, even in old age. Since many fundamental metabolic pathways in fruit flies are shared with humans, this study suggests that human metabolism might respond similarly and that people on high-calorie diets might benefit from a reduction in their caloric intake in old age. Researchers are currently analyzing data from female fruit flies to see if there are sex-related differences in response to the change in diet.