The fourth installment in this bestselling series of scientifically based advice offers practical guidance on one of the most important aspects of our lives -- health.

The Simple Science of a Healthy Life

From fitness to diets to emotional health and longevity, what do people who feel and look healthy do differently than those who are overtired, depressed, or out of shape? Every day we face an avalanche of studies and statistics that tell us what we should or shouldn't eat, how long we need to exercise, or how to protect ourselves from secondhand smoke and the harmful rays from the sun. Not only are these studies often contradictory, but the actual scientific information is usually inaccessible.

Moving beyond the myths and misinformation, the advice in these pages is not based on one person's opinions or one expert's study. For the first time the research available on the health of average Americans has been distilled into one hundred essential ways that we can become healthier and happier. Each of the core findings is accompanied by a real life example showing these results in action.

• Eat more often. Oxford University researchers found that people who ate five or six times a day had a 5 percent lower total cholesterol than average and were 45 percent more likely to be able to sustain their target weight than people who ate once or twice a day.
• Who says caffeine is bad for you? The majority of scientific evidence shows that, for a healthy adult, moderate quantities of caffeine (about three cups of coffee per day) pose no significant health risks.
• Home sweet home. People who described their home lives as satisfying were 24 percent more likely to live beyond normal life expectancy, according to a UCLA study.

When a house is built, all the steps of the process have to be considered before construction starts. Otherwise, you could wind up installing the doors and then finding out the refrigerator won't fit through them. Similarly, your health plans have to be considered together as a whole instead of one piece at a time. Your chances of sticking to a health improvement plan -- eating right, exercising regularly, or quitting smoking -- are higher if you focus on your overall health rather than just the task at hand. In other words, think about the things that you could do to improve your health and how they fit together, and each act will reinforce everything else you are trying to do.

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Six years ago, Lee was hobbling around with a cane. Now the seventy-two-year-old Chicago area man pumps iron for more than two hours a day several times a week. "I call it a lifestyle change," he says.

"There was a time when I wasn't in very good shape. I was about fifty pounds too heavy, had swelling in my knees, and was loaded with arthritis," he says. But he got tired of living like what he calls an "old man."

"I did research on nutrition, read studies and books on preventing aging," Lee says. He started changing his diet and exercising. "I have seen so many improvements. I sleep better, have more energy, stopped having stomach problems, and my aches and pains went away."

Lee adds, "I feel like I'm forty."

Now Lee is taking his enthusiasm for healthy living on the road. He speaks about nutrition and exercise to various community groups and is putting together his health tips on a Web site.

One of his biggest fans is Kristina, who is forty years younger than Lee. "I heard him give a presentation, and I was so impressed with Lee. He asked me if I was ready to change my life and I said I was," Kristina said. She has since changed her habits and feels better than ever. "If anyone would have told me a seventy-two-year-old retiree would change my life, I wouldn't have believed it," she said, "but now I know better."

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Dana-Farber's Center for Community-Based Research studied workplaces where employers provided health, safety, and quitting smoking programs as one comprehensive service, and workplaces where such programs were offered separately. At the end of two years, the investigators found that more than twice as many workers quit smoking and maintained a healthy diet in the comprehensive service as in the separate programs.