Eat Less, Live Longer?

ROS damage the building blocks of life, including protein, lipids and genetic material, DNA. This leads to abnormal genetic signals, causing cancers and disregulation of cells, leading to organ damage, skin deterioration, and maybe even gray hair -- all signs of aging.

• Calorie restriction reduces inflammation, which is one cause of many diseases, such as heart disease and arthritis. Also, calorie restriction reduces some "growth factor" hormones.

"When you eat extra calories, your body gets a signal that you're growing and growth factor hormones promote cell proliferation, which may increase the risk of cancers, among other dangers," says Fontana.

• Calorie restrictors also have lower hormone levels, body temperatures, plasma insulin levels, and higher levels of the hormone, DHEA. The same is also true about people who live longer, according to the Baltimore Longitudinal Study on Aging, an ongoing study funded by the National Institutes of Health.

• Calorie restriction reduces body fat, which research shows has many benefits.

"We used to think body fat was inert, But it isn't," says Fontana. "Fat tissue produces hormones, pro-inflammatory chemicals, which regulate metabolism, the immune system, inflammation and the progression of artery hardening, so that when you have less body fat, you get many biological benefits."

There are many advantages to calorie restriction. But there are downsides to severe calorie restriction, too. In fact, scientists are not recommending it as a key way to stay healthy, since the research is not complete. Abnormally low metabolism can cause irritability or depression in some people or may backfire and lead to an eating disorder. If you eat too few calories and hormone levels lower too much, this may lead to infertility problems or increase chances of osteoporosis in women.

I believe that one of the real benefits of the low-calorie approach is that it places important emphasis on the central issue: reducing calories, rather than getting diverted into seemingly important, but in fact, peripheral matters, such as carb and fat counting.

Katherine Tallmadge is a Washington nutritionist and author of "Diet Simple" (Lifeline Press, 2004). Send e-mails to her at food@washpost.com.