Sex difference in pathology of the ageing gut mediates the greater response of female lifespan to dietary restriction

Women live longer than men, and many age-related diseases are more common in one sex than the other. In addition, some treatments that extend the healthy lifespan of laboratory animals are more effective in females than in males. These include dietary restrictions, where food or specific dietary constituants are kept in short supply. Stem cells can help to repair old and damaged tissue because, when they divide, they can form a cell that can specialize into one of several mature cell types. Previous studies of the fruit fly Drosophila melanogaster have shown that stem cell activity in the gut affects how long female flies live. Now, Regan et al. have looked in detail at the guts of male and female fruit flies as they age. This revealed that female guts deteriorate as the flies grow old because the stem cells in the gut divide more often and form small tumours. These stem cells help young females to grow and repair their guts, but start to turn against them as they age. In contrast, male guts stay well maintained and do not show the same signs of ageing. Females fed less food had guts that aged more slowly, suggesting they might live longer on a restricted diet because it improves their gut health. Regan et al. then used a genetic trick to make male flies with female guts. These feminized males had more gut tumours than normal males, but they also showed a greater increase in lifespan when placed on a restricted diet, because the poorer condition of their ageing gut meant there was more scope for the diet to improve their health. So if gut deterioration does not limit male lifespan, what do males die of? Pursuing this question may ultimately help us to understand how human lifespans are affected by sex differences and develop treatments for ageing and age-related diseases that everyone can benefit from.