Genetically altered mice appear to be eating what they want, staying slim and living a long, healthy life. And uncovering exactly how they do it could lead to new ways to fight obesity and other chronic diseases like diabetes.
The Harvard scientists found that mice lacking insulin receptors in their fat tissue stayed lean and lived long lives despite their healthy appetites. They say the findings support the idea that "leanness," and not the number of daily calories per se, is what makes for longer life in mammals.
According to the researchers, the mice were able to stay slim while eating whatever they wanted because their fat tissue could not respond to the hormone insulin. After meals, insulin helps shuttle sugar from the blood and into body cells to be used for energy. The hormone also helps fat cells store fat.
Just how relevant the new findings are to people is unclear. But they open up the possibility that a drug designed to specifically block insulin receptors in fat tissue could help fight obesity--and maybe tack some time onto people's lives.
A body of evidence already suggests that a low-calorie lifestyle can lengthen the life spans of everything from yeast to mammals. But exactly why this is remains unknown.
The new research suggests that longevity depends more on the amount of fat a body packs than on food restriction itself.
This runs counter to a prevailing theory on why calorie restriction equals longer life in many organisms. This theory holds that less food slows the metabolism, which in turn produces fewer oxygen free radicals--cell-damaging substances that are a natural byproduct of metabolism.
But the insulin-receptor-deficient mice in the new study ate as much as their littermates while staying svelte--suggesting that their metabolism was actually revved up. And with this apparently speedy metabolism, the lean animals lived 18% longer than their normal counterparts, on average. Their maximum life span was extended by about 5 months.
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