Even though the rodents ate more food than normal mice they had less fat and lived longer.
Clever genetic detective work may have pinpointed the reason why a near-starvation diet prolongs the life of many animals.
Ronald Kahn at Harvard Medical School in Boston, US, and his colleagues have been able to extend the lifespan of mice by 18 per cent by blocking the rodent's accumulation of fat in specific cells. This suggests that leanness - and not necessarily diet - promotes longevity in "calorie restricted" animals.
The experiment was done by knocking out (ie disabling or removing) a gene that codes for the insulin receptor found on fat cells. Without this receptor the fat cells had no way of being told by insulin to pick up sugar from the blood. Hence the fat cells couldn't get the raw materials they needed in order to be able to make and store fat. The consequence was a substantial boost in life expectancy.
As a consequence of this modification, they cut off the fuel supply that enables the body to lay down fat.
These "Firko" (fat-specific insulin receptor knock-out) mice ate normal diets but had reduced fat mass and lived 18 per cent longer on average than normal mice. Even when they were made to overeat, they stayed lean.
While calorie restriction (CR) typically boosts life even more (30% in some cases) this result tends to suggest that one mechanism by which CR works is by reducing the amount of stored fat. Recent research results on the risks of intra-abdominal fat suggests a number of mechanisms by which a reduction in fat will increase life expectancy.
Reducing intra-abdominal, or visceral, fat is important because in addition to increasing the risk of cardiovascular disease and diabetes, among other conditions, such fat can raise insulin levels, which promotes the growth of cancer cells.
People with high levels of intra-abdominal fat may not even know it, McTiernan said, because it is hidden, deposited around the internal organs within the abdomen. "Most women don't know about intra-abdominal fat, but they should, since it is the most clinically significant type of fat and it's where women tend to store fat after menopause."
Although it is known that so-called "apple-shaped" people who store their fat around the stomach are at higher risk for conditions such as diabetes, hypertension and stroke than "pear-shaped" people who store their fat in their buttocks and thighs, visceral obesity is not necessarily correlated with body shape, McTiernan said. The only accurate way to determine the presence and extent of intra-abdominal fat is with imaging procedures such as CT or MRI scans.
|Share |||Randall Parker, 2003 January 24 01:36 AM Aging Reversal|