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News--
A lean body may mean a long life: study
By Amy Norton Jan 23, 2003
NEW YORK (Reuters Health) - Eat what you want, stay slim and live a long,
healthy life. It's a dream to humans, but some genetically altered mice appear
to be living it, according to a study released Thursday.
And uncovering exactly how they do it could lead to new ways to fight
obesity and related ills like type 2 diabetes, according to researchers.
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,
according to study author Dr. C. Ronald Kahn.
"This suggests a new way of thinking in drug
development," he told Reuters Health.
But any drug
that would mimic the effects seen in these lab mice would have to be finely
targeted to fat only, Kahn noted. That's because in people, loss of insulin sensitivity
throughout the body leads to type 2 diabetes.
Kahn
and his colleagues at Harvard Medical School in Boston, Massachusetts, report
the findings in the January 24th issue of Science.
A
body of evidence already suggests that a low-calorie lifestyle can stretch the
life spans of everything from yeast to mammals. But exactly why this is remains
unknown.
According to Kahn, 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 that's not what's
happening" in these mice, Kahn said.
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 brethren, on average. Their maximum
life span was extended by about 5 months.
One of the
next steps, Kahn said, is to find out what it is about body fat that affects
longevity. If the free-radical byproducts of metabolism are not the big
determinants of life span, he explained, "maybe some of the damaging substances
come from fat."
SOURCE: Science 2003;299:572-574.
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