Switching to a rich diet after a restricted diet can lower life expectancy and have negative effects on health, new research suggests.
Experts tested an existing evolutionary theory that dietary restriction – reducing a particular or total nutrient intake without causing malnutrition – triggers a survival strategy.
The theory suggests that humans and animals invest in maintaining and repairing the body in times of low food availability, to wait for when it increases again.
But the new findings from the Healthy Lifespan Institute at the University of Sheffield and Brown University in the USA, published in Science Advances, challenge the theory.
Researchers found that fruit flies fed a restricted diet and then returned to a rich diet were more likely to die and laid fewer eggs compared with flies that spent their whole life on a rich diet.
This demonstrates that, rather than waiting for food availability to increase in the future, the flies were essentially waiting to die on a restricted diet, the scientists suggest.
They add that, instead of dietary restriction increasing repair and maintenance mechanisms, it could actually be an escape from the damaging effects of a rich diet.
PhD student Andrew McCracken, from the University of Sheffield’s Department of Animal and Plant Sciences, who led the study, said: “Dietary restriction is an unusual paradox which has attracted a great deal of interest within the field of ageing.
“Our results have now pointed us towards a more refined explanation of why it occurs, and have the potential to wholly shift the focus of future research.
“Our most surprising finding was that, under certain circumstances, restricted diets can also be the origin of particular types of damage to the individual.
“This enhanced understanding of the penalties and benefits of certain types of diets will expedite the quest to identify pharmaceutical interventions which mimic dietary restriction.”
Dr Mirre Simons, also from the university’s Department of Animal and Plant Sciences, said: “The effects of diet on health are huge, but we understand little of the exact mechanisms.
“Our work has now uncovered a surprising property of dietary restriction, in that it makes flies ill-prepared for rich diets.
“This was contrary to our expectations and contrary to current evolutionary theory.”
The scientists add that their findings suggest that changing diet repeatedly or abruptly could be harmful to health in certain situations.
The research was funded by the National Environment Research Council (NERC), Wellcome, the American Federation for Aging Research and the National Institute on Aging.