What is it about?
Diet can change how long animals live and how well they reproduce, but these effects are not always simple. Here, male fruit flies were fed specially defined diets to test how lifespan and reproductive success depend on two aspects of nutrition: the balance of protein and sugar, and the presence of cholesterol. Cholesterol is a sterol — a type of nutrient that fruit flies cannot make for themselves and must obtain from food. Because cholesterol is not used as fuel, manipulating it makes it possible to ask whether a non-energy-yielding part of the diet can still shape ageing and reproduction. The effect of cholesterol depended strongly on whether males were mating. When males had regular access to females, removing cholesterol from the diet shortened their lives. But when males were kept without females, cholesterol was not always beneficial and could even be costly. This shows that the same nutrient can have very different effects depending on an animal’s reproductive situation. The diet that helped males live longest was also not the same as the diet that helped older males reproduce best. By comparing males kept with and without females, the authors were able to show that this nutritional trade-off is closely tied to mating. Without allowing males to mate throughout life, an important part of the relationship between diet, reproduction, and ageing would have been missed.
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Why is it important?
Studies of diet and ageing often focus on how to extend lifespan, but lifespan is only one part of biology. Animals also need to reproduce, and the nutritional conditions that favour one may not favour the other. This study challenges the idea that male reproduction is biologically cheap or easy to ignore. To understand how diet affects ageing, we need to consider not only what animals eat, but also what they are doing with those nutrients.
Perspectives
For me, this project was driven by a concern that standard experimental designs may underestimate the costs of male reproduction. Many studies allow males to mate only briefly, keeping them without females for most of their lives. That makes experiments easier to manage, but it does not give males the opportunity to invest in reproduction in a sustained, realistic way. This links to our main finding: removing cholesterol shortened lifespan only when males were allowed to mate throughout life. Previous work had suggested that cholesterol depletion had little effect on male lifespan, so this result highlighted how strongly the outcome can depend on the conditions under which animals are studied. The project also produced an unexpected result in the broader nutritional landscape: the protein-to-sugar ratio that maximized lifespan was very different from what has often been reported previously. That is an unusual finding, and one that deserves further investigation. Overall, this study reinforced for me that context matters. If we want to understand how diet shapes ageing, especially in males, we need to pay closer attention to reproduction and to whether our experiments actually allow animals to express the biology we are trying to measure.
Andrew McCracken
University of Liverpool
Read the Original
This page is a summary of: Mating-dependent lifespan cost of sterol depletion in male
Drosophila melanogaster, Proceedings of the National Academy of Sciences, June 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2533735123.
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