Courtesy of caloric restriction, the monkey on the left may be looking toward a longer, more active and healthier life than the monkey on the right, which gets to eat its fill. Courtesy of the National Institute on Aging Dietary Restriction Project.
When less is more
POSTED 5 FEB 1998 We don't know John Glenn's longevity secret, but we've heard one that sounds almost convincing enough to persuade us to decline that third slice of cheesecake.
However you slice it, it turns out that the only reliable way to extend the lifespan of rodents, spiders, guppies and water fleas is to drastically cut calories without skimping on essential nutrients. It's a technique scientists call undernutrition without malnutrition.
And we're not talking any Slender Centers diet. We're not talking about substituting a grapefruit for the occasional ice-cream sundae. We're talking about feeding lab animals as little as two-thirds of the calories they'd eat if nobody was watching. (The Why Files covered the health effects obesity.)
Although it has yet to be systematically tested in people, this kind of serious undernutrition extends both average and maximum lifespans. In rats, for example, a 30 percent cut in calories stretches the average lifespan by 30 percent.
And it's not just longevity -- these animals don't get the ailments of aging -- cardiovascular disease, diabetes and cancer -- until much later in life. And while we haven't heard about the guppies or water fleas, the rats' little brains continued mastering mazes long after rats on a typical all-you-can-eat diet quit learning.
The phenomenon, discovered about 70 years ago, remained a laboratory novelty until the 1970s, when scientists began realizing that the ever-sought fountain of youth might consist of simply cutting calories.
"Until 1987, caloric restriction was never tried in a controlled way with animals that live longer than three years," says Roth. A decade later, we're finally accumulating information on how caloric restriction affects primates.
The new results mirror data from lower animals, meaning they may be depressing to those of us who love to eat. The monkeys are being fed 30 percent less than they would eat on their own. Echoing studies with rodents and water fleas, caloric restriction in primates seems to be slowing the diseases of aging:
|Measures of body temperature, weight, lean mass and fat are below those of free-feeding animals.|
|Biological markers of aging, such as blood pressure, "good" cholesterol and triglyceride levels, are improved. "Taken all together, we predict they will be less likely to develop cardiovascular problems," Roth says.|
|The blood-borne hormone insulin is better able to help metabolize sugar. Since impairment of this so-called "insulin efficiency" can signal adult-onset diabetes, Roth says "this suggests that they are less likely to develop diabetes as they age."|
|Levels of DHEA -- a hormone produced by the body that seems to be a "marker" of the rate of aging -- are dropping more slowly than usual.|
In other words, the animals don't just look small and hungry. They look healthy. Since the squirrel and rhesus monkeys in the experiment normally live 20 and 30 years, respectively, it's far too soon to tell if they'll outlive the free-feeding control monkeys. Still, Roth speculates that, "Current findings strengthen the possibility that caloric restriction might extend the lifespan" in these monkeys.
But are the monkeys happy?
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The Why Files Staff includes: Terry Devitt, editor; Darrell Schulte, webmaster; Dave Tenenbaum, feature writer; Susan Trebach, team leader.