Dietary restriction – reduced food intake without malnutrition prolongs life span in yeast, worms, flies, rodents, monkeys and possibly humans.
But dietary restriction also often impairs fecundity, possibly because maintenance of the overall body mass (the non -germline parts of an organism), and thus long life, do not give space for reproductive activity.
Biologists have long thought that an organism’s response to food shortage is an evolutionary device that allows individuals to survive a famine by diverting resources away from reproduction and reallocating them to essential functions for survival
Grandison et al in Nature 2009 report that this idea is almost certainly wrong. They find that dietary amino acids are respon¬sible for shortening lifespan and increasing reproduction in the fruitfly Drosophila mela¬nogaster, but that both longevity and fecun¬dity can be maximized when intake of these nutrients is finely tuned.
It has become clear that rich diets shorten life, not because of excess calories but rather because of dietary imbalance, with lifespan and fecundity being maximized at different nutritional optima, Specific nutrients are implicated in dietary restriction, especially amino acids, Reducing the intake of casein, a major amino-acid source, extends lifespan but decreases fecundity in Drosophila. Simi¬larly, methionine restriction promotes lon¬gevity in flies, rats and mice..
In a series of painstaking experiments, Grandison et al fed female flies a restricted diet that extends lifespan at the expense of fecundity, and then tried to restore the short¬life and high- fecundity characteristics of fully fed flies by adding back specific nutrients. Adding carbohydrates, lipids or vitamins made no difference. But adding amino acids short¬ened lifespan and increased egg production to the level observed under full feeding..
Grandison et al. found that adding all non-essential amino acids only marginally shortened lifespan and did not change fecundity, whereas adding all essential amino acids decreased lifespan and increased egg production as much as combin¬ing all amino acids or full feeding.
Methionine alone increased fecundity as much as full feeding but without reducing lifespan. Methionine together with one or several other essential amino acids is responsible for the life span-shortening effect of full feeding.
The benefits of methionine might be through the IIS-insulin /insulin-like growth factor (IGF) pathway .
If the present results’ in the fly are gener¬ally applicable, even mammals might be able to enjoy a long life without loss of fecundity by virtue of a suitably balanced diet.
Flat 2009 Diet and longevity in the balance Nature vol 462 pp 989-990
Grandison et al 2009 Amino acid imbalance explains extension of life span by dietary restriction in Drosophila.Nature vol 462 pp 1061-1064
- Martin Eastwood