Human obesity and lessons from the very hungry caterpillar

12 September 2006

A leading University of Sydney researcher's caterpillar experiment has, for the first time, provided evidence that animal populations can adapt over time to high energy diets by limiting the amount of fat they put down.

Diamondback Moth Plutella xylostella The caterpillars used in the study More Information ROLLOVER

In the study Professor Simpson and his colleagues took hundreds of caterpillars reared over generations on a stable diet containing equal proportions of carbohydrate and protein (26% of each). They then divided the population into two groups. One group was fed a high protein diet (45% protein and 7% carbohydrate), the other was fed a high carbohydrate diet (12% protein and 40% carbohydrate).

"We tested the caterpillars, which have a life span of roughly two weeks, after the 1^st, 4^th and 8^th generations, and found that those in the high carbohydrate environment developed the tendency not to lay down excess fat," Professor Simpson said. "In contrast, those caterpillars in the high protein, low carbohydrate environment evolved an enhanced capacity to store away any available carbohydrates as fat."

Caterpillars with a tendency to become obese were less likely to survive (and therefore pass on their genes) in a high carbohydrate world. "This is the first time anyone has shown an evolutionary cost to having excess body fat, and that such a cost is worth paying in environments where carbohydrates (or fat) are scarce," Professor Simpson said.

But the traits that evolved in both groups came at a cost, says Professor Simpson. "Animals that have evolved in a high carbohydrate environment would be at risk of starvation if the source of energy in their environment suddenly decreased. On the other, hand those reared in a high protein environment have a high risk of obesity in a high carbohydrate world."

"Obesity in human populations has only been an issue for about two generations, and so far humans of reproductive age haven't paid the price. But for the first time we are seeing obesity-related health problems such as type 2 diabetes affecting significant numbers of reproductive-aged and pre-reproductive aged humans. This raises the possibility that our diet could significantly influence our genetic evolution over the next few generations."

Source / Credit: University of Sydney