You are what you eat, but does it matter when you eat it?

We all know the expression “you are what you eat” but do juvenile diets determine your adult size or can adult diets change things? Gonçalo Poças, Alexander Crosbie and Christen Mirth have used a model organism – the fruit fly Drosophila melanogaster – to explore this question.

They found that while larval nutritional conditions play the dominant role in determining both adult body weight and appendage size in D. melanogaster, the adult diet can adjust body weight as the flies age.

The team manipulated both the quality and energy quantity of diets that larval and adult flies received in two experiments.

In the first experiment calorie content was held stable but the ratio of protein to carbohydrate was either 1:2 (high quality) or 1:10 (low quality). In the second experiment flies were fed a high quality diet but with two different calorie contents. The low calorie content diet was 25% of the high calorie diet.

Importantly, larvae were reared on one of the two diets in each experiment and then after “eclosing” (emerging as an adult) they either remained on the same diet or were switched to the alternative diet. This allowed the researchers to tease apart at what life-stage diet was most influential in determining measures of adult size.

Adult weights, wing area and femur size were measured at 3, 10 and 17 days old. The team predicted that adult weight would be more influenced by adult diet but that wing area and femur size would be determined by larval diet.

Schematic of the experimental design. Larvae were fed alternative diets in two experiments that looked at the quality of the diet or the energy content of the diet. Once flies emerged as adults they were kept on the same diet or switched to the other diet and measures of size were taken at 3, 10 and 17 days.

For the most part, the team found that the larval diet contributed more to differences in adult weight, wing area, and femur size in both males and females, but the quality of the larval diet had greater effects on adult size than the calorie content.

In addition to the effects of larval diet on adult size traits, Gonçalo and his colleagues found that animals subjected to poor larval nutrition were able to increase their body weight if maintained on good quality diets during the adult stages.

One surprising result the team uncovered was that the adult femur size changed with age, and depended on both the larval and adult diet. This suggests that the size of adult appendages might not be as fixed as previously thought.

So, to return to our initial question. Yes, the juvenile diet is very important in determining measures of adult size, but adult diets can make up for nutritional deficiencies in earlier life to some extent – in fruit flies at least.

This research is currently in press in the Journal of Insect Physiology.