THE best thing to eat to extend your lifespan is very little. Why caloric restriction should lengthen life isn't clear, but it now seems that growth hormone could well be a key piece in the puzzle.
Andrzej Bartke and colleagues at Southern Illinois University in Springfield worked with normal mice and mutant mice missing the receptor for growth hormone. Half of each type were allowed to eat at will, and the other half were fed 30 per cent fewer calories than usual. As expected, normal mice on fewer calories lived 20 to 30 per cent longer. Mice without the growth hormone receptor also showed similar increases in longevity on a normal diet.
This suggests that restricting calories has a similar effect on the body to knocking out the growth hormone receptor. Doing both does not make the mice live even longer: the mutant mice on low-calorie diets had similar lifespans to those on the normal diet.
"The actions of growth hormone are somehow implicated in linking caloric restriction to longer life," Bartke says. Insulin may be the connection. Both groups of long-lived mice had a greater sensitivity to insulin, and caloric restriction in the mutant mice failed to increase their strong insulin sensitivity any further.
"Insulin resistance is a risk factor for just about any problem you don't want to get: diabetes, atherosclerosis, cancer. It's sort of intuitive that the opposite situation would be beneficial."
