Back in the 1930s, scientists noticed water fleas and rats fed restricted diets while young lived longer. The same effect has since turned up in fruit flies and mice. A recent Nature study led by Fumiaki Obata, a biologist at the RIKEN Center for Biosystems Dynamics Research in Kobe, Japan, found a protein that carries a record into adulthood of what fruit flies ate as larvae, influencing how long they live.

In Obata’s experiment, fruit flies fed a low-protein diet as larvae outlived their well-fed siblings, but were paler and lighter, weighing sometimes 28 percent less. The females also laid fewer eggs. Adding amino acids back eliminated the lifespan boost. The team called this nutritional memory and set out to find where it was kept.

Comparing gene activity turned up around 100 candidate proteins. Using stable isotopes, they found that three days into adulthood, nearly 64 percent of proteins in the flies’ heads were still made from amino acids eaten by larvae. By day six, that dropped to about 46 percent. Prominent among them were ribosomal proteins. They identified a storage protein called larval serum protein 2, or Lsp2, that responds to larval diet and survives metamorphosis. Larvae stockpile it as a pantry for metamorphosis when they stop eating.