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Is Thinner Always Better Can weight determine how long you'll live?
 If you can survive the hunger pangs, it sounds like a pretty good deal: Eat less than a supermodel and, in turn, tack a few decades onto your life. Research has shown that ultra-low-calorie diets can improve the longevity of other animals, so why not humans too?
While you may have heard the hype about extreme "calorie restriction" -- cutting your food intake by 30 or 40 percent indefinitely -- some experts say it's a bad idea.
"In a nutshell, don't do it," advises Lona Sandon, a spokeswoman for the American Dietetic Association. "You need to be sensible about how you approach weight loss, and starvation is not a sensible approach."
To be fair, the aim of calorie restriction (CR) is not starvation. Calorie-restricted diets for longevity are about obtaining the maximum amount of nutrition in the smallest amount of calories by eating only nutrient-dense foods. What does this diet look like? No simple sugars or carbohydrates; plenty of vegetables, especially green, leafy ones; and protein from sources with little to no saturated fats. As you might have guessed, people who subscribe to these diets end up losing a significant amount of weight, at times looking almost emaciated. This begs the question, is a skeletal physique the image of vitality and long-lasting youth?
Perhaps not. This past April, the government released a report suggesting that slightly overweight people live longer than not only underweight people, but those of normal weight as well. This was good news for those of us who were never going to see a size four again -- as if we ever had in the first place. The study from the U.S. Centers for Disease Control and Prevention (CDC), published in the prestigious Journal of the American Medical Association, made many Americans rejoice, and many scientists scratch their heads.
A few weeks later, that very study was refuted by CDC director Dr. Julie Gerberding. "We have had a dramatic increase in the proportion of people in our world that have obesity," she said in a news conference. "That constitutes, in my view, a serious epidemic."
Gerberding indicated the problem with the study was with the way causes of death are officially reported. "Obesity is not listed on death records," she explained. "We have to rely on extrapolations." And that, she implied, is why it appeared that someone a bit zaftig might appear to live longer than someone within normal weight guidelines.
So, if we assume the CDC statistics were nothing more than a glitch, is it better to be underweight? There's some evidence that skinnier species of some animals live longer. Scientists have found that they can lengthen the lifespan of rats by a third by cutting their calorie consumption by 30 to 40 percent. Cutting a rat's food in half, though, does not offer the same life-lengthening benefits.
And that's not all. The link between less food and longer life "seems to be generally true in many species," says Lenny Guarante, professor of biology at the Massachusetts Institute of Technology and a specialist in aging. It's not entirely clear whether caloric restriction works in humans too, although some research suggests it's possible. The first human studies of the effects of CR are now underway at several institutions.
For now, "the challenge is to figure out how it works," Guarante says. After all, animals and people seem to be programmed to eat hearty meals when they can. Just check out your dog's appetite or your brother-in-law's ability to chow down an entire steak in one sitting. Why on earth would cutting back on food be a good thing?
Longer lives come at a price. Rats on severe diets lose a third of their body weight. And humans who've tried similar diets have ended up with the chills -- thanks to the loss of body fat -- and lowered s-e-x drives.
There are other potential problems too. While people on the diets may stop feeling hungry after a while, they'll also lose muscle mass and may suffer from malnutrition, says dietician Sandon, an assistant professor at the University of Texas Southwestern Medical Center, Dallas. These diets are very strict and calculated. Subscribers to CR may unwittingly be malnourishing themselves if they're not extremely careful.
So what should you do? Well, you could hope that scientists will figure out a way to harness the power of calorie restriction in a pill. Think we're joking? Guarante says researchers are already on it.
Or you could try to live longer by living healthfully. "There's plenty of research to say that if you maintain a normal body weight and you stay physically active, you're going to live longer," Sandon says. "Unless you're run over by a truck."
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