Dietary restriction fails to extend life in stressful environments

Abstract

Moderate dietary restriction often prolongs life in laboratory animals, and this response has been interpreted as an adaptive strategy that promotes survival during famine. However, dietary restriction can also increase frailty, and it therefore remains unclear whether restricted diets prolong life under stressful conditions like those experienced by wild animals. We manipulated adult dietary protein of Drosophila melanogaster across a gradient of ambient temperature, and examined effects on survival. To test for trade‐offs, we also quantified reproduction, and performance of F1, F2 and F3 descendants. We found that protein restriction increased longevity of one or both sexes at benign ambient temperatures (25°C and 27°C), but failed to extend longevity of flies maintained in cold (21°C and 23°C) or hot (29°C) conditions. Instead, in females, protein restriction resulted in strongly elevated mortality at cold temperatures. Protein restriction also generally reduced reproductive performance, and did not consistently enhance performance of F1, F2 or F3 descendants. Taken together, our results challenge the long‐held idea that extended longevity of diet‐restricted laboratory animals represents an adaptive survival strategy in natural populations. Our findings suggest instead that this response is an artefact of benign laboratory conditions, and that DR‐induced life extension might not be achieved in the more stressful conditions experienced in the wild. Read the free Plain Language Summary for this article on the Journal blog.

Dietary restriction extends lifespan across different temperatures in the fly

“…These authors (Zajitschek et al, 2023) considered 25°C to be a low temperature for flies as it is lower than the ambient temperature in the climate of origin for the species. However, most experimental lines of flies will have been inbred or bottlenecked for many years under laboratory conditions, often at 25 °C.…”

“…Moreover, DR can arguably only be interpreted as absent when in the same study routine conditions result in a DR phenotype. A recent example of DR not extending lifespan of flies ( Drosophila melanogaster ) at lower temperatures has been interpreted as DR being a lab artefact with low temperature interpreted as representing stressful conditions (Zajitschek et al, 2023). There are several questions that can be posed to this study, for example: why did DR not extend lifespan at the most regularly used lab temperature of 25°C?…”

“…We suggest the most reasonable test of the hypothesis posited by this recent work questioning DR, is to start with a strain that reliably and repeatedly shows DR under standard temperatures to then test whether lower temperatures negate the DR response. We use substantially larger sample sizes per treatment group ( N is between 313 and 487 females) compared to the work that led to this hypothesis ( N = 100) (Zajitschek et al, 2023).…”

Dietary restriction extends lifespan across different temperatures in the fly

“…Moreover, DR can arguably only be interpreted as absent when in the same study routine conditions result in a robust and repeatable DR phenotype. A recent example of DR not extending lifespan of flies (Drosophila melanogaster) at lower temperatures has been interpreted as DR being a lab artefact with low temperature interpreted as representing stressful conditions (Zajitschek et al, 2023). There are several questions that can be posed to this study, for example: why did DR not extend lifespan at the most regularly used lab temperature of 25°C in females, the most studied sex in this paradigm?…”

“…We suggest the most reasonable test of the hypothesis posited by this recent work questioning DR, is to start with a strain that reliably and repeatedly shows DR under standard temperatures to then test whether lower temperatures negate the DR response. We use substantially larger sample sizes per treatment group (N is between 253 and 505 females) compared to the work that led to this hypothesis (N = 100) (Zajitschek et al, 2023). We further used a broad range of five diets to be able to distinguish a shift from a change in shape of the DR lifespan reaction norm (Simons & Dobson, 2023).…”