The relationship between longevity and diet is genotype dependent and sensitive to desiccation

Abstract

Dietary restriction (DR) is a key focus in ageing research. Specific conditions and geno-types were recently found to negate lifespan extension by DR, questioning the universal relevance of DR. However, the conceptual framework of dietary reaction norms explains why DR's effects might not be apparent in some situations. When dietary reaction norms shift with genetic or environmental effects, a specific dyad of diets tested can result in a null effect. Only if a full reaction norm is tested can lifespan (or any trait) be shown to be refractory to diet. We tested comprehensively, for the first time, the importance of dietary reaction norms by measuring longevity and fecundity on five diets in five genotypes, with and without water supplementation, using high sample sizes in the fly (N>25,000). We detected substantial genetic variation in the reaction norm between diet and lifespan. Environments supplemented with water rescued putative desiccation stress but only at the richest diets. Fecundity declined at these richest diets, but contrary to effects on lifespan, was unaffected by water and is thus most likely caused by nutritional toxicity. Our results demonstrate empirically that any conclusion on the absence of DR is only justified when a range of diets is considered in a reaction norm framework. D desiccation

The hidden costs of dietary restriction: Implications for its evolutionary and mechanistic origins

“…Our rich and restricted diets induce consistent life-span differentials. Moreover, recent work carried out using a wider range of diets suggests that our diets are in the area of largest response for most genotypes (59). Restricted media retained the composition of all other media components, given the dietary protein axis is the main lifespan determinant in flies (3,5).…”