Stay the weight you were at 18

1. "Next to not smoking, this is probably the most important thing we can do to stay healthy and live longer," says Walter Willett, MD, chair of the department of nutrition at the Harvard School of Public Health.

Leanness matters for how to look younger, because fat cells produce hormones that raise the risk of type 2 diabetes. They also make sub-stances called cytokines that cause inflammation--stiffening the arteries and the heart and other organs. Carrying excess fat also raises the risk of some cancers. Add it up, and studies show that lean people younger than age 75 halve their chances of premature death, compared with people who are obese.

The government deems a wide range of weights to be healthy (between 110 and 140 pounds for a 5-foot-4 woman), partly because body frames vary tremendously. So to maintain the weight that's right for you, Willett suggests you periodically try to slip into the dress you wore to your high school prom--assuming, of course, that you were a healthy weight at that age. If not, aim for a body mass index of about 23.5.

Willett can't use the prom-dress test himself. Nevertheless, at 6-foot-2 and a lean 184 pounds, he dutifully hews to the BMI of his youth.

2. Take the dynamic duo of supplements

They're what Bruce N. Ames, PhD, a professor of biochemistry and molecular biology at the University of California, Berkeley, swears by: his daily 800 mg of alpha-lipoic acid and 2,000 mg of acetyl-L-carnitine. In these amounts, he says, the chemicals boost the energy output of mitochondria, which power our cells. "I think mitochondrial decay is a major factor in aging," Ames says--it's been linked to diseases such as Alzheimer's and diabetes.

In his studies, elderly rats plied with the supplements had more energy and ran mazes better. "If you're an old rat, you can be enthusiastic," Ames says. "As people, we can't be sure until clinical trials are done." (They're under way.) But the compounds look very safe--the worst side effect documented in humans is a rash, Ames says--and "the data in animals looks really convincing," says S. Mitchell Harman, MD, PhD, president of the Kronos Longevity Research Institute in Phoenix.

3. Skip a meal

This one move could have truly dramatic results for how to look younger. Rats fed 30% less than normal live 30% longer than usual--and in a recent study at the Washington University School of Medicine in St. Louis, the hearts of the leaner human calorie-cutters appeared 10 to 15 years younger than those of regular eaters.

In other research, calorie restrictors improved their blood insulin levels and had fewer signs of damage to their DNA. Eating less food, scientists believe, may reduce tissue wear and tear from excess blood sugar, inflammation, or rogue molecules known as free radicals.

Edward Calabrese, PhD, and Mark Mattson, PhD, have opted for "calorie restriction lite." Calabrese, a professor of toxicology and environmental health sciences at the University of Massachusetts, Amherst, dumped the midday meal. Mattson, chief of the laboratory of neurosciences at the National Institute on Aging, has done without breakfast for 20 years.

Try it Skip a meal a day. You don't need to try to cut calories; Mattson's research suggests you'll naturally consume less that day. Or try fasting one day a week. Just drink plenty of water.