THE MAGIC OF EXERCISE Suppose there was a potion that could keep you strong and trim as you aged, while protecting your heart and bones improving your mood, sleep and memory warding off breast and colon cancer, and reducing your overall risk of dying prematurely. Studies have shown that exercise can have all those benefits—even for people who take it up late in life. Kin Narita and Gin Kanie, Japanese twins who are national longevity icons, celebrated their 105th birthday last week by planting trees and playing golf for the first time. Kanie suggested that activity might be a key to their long lives. 'At this age I walk for two hours each morning for exercise,' she said. When Dr. Ralph Paffenbarger started tracking the health of 19,000 Harvard and University of Pennsylvania alumni back in the early 1960s, many experts thought vigorous exercise was downright dangerous for people over 50. But the Stanford epidemiologist turned that wisdom on its head. In a landmark 1986 study, Paffenbarger showed that the participants' death rates fell in direct proportion to the number of calories they burned each week. Those burning 2,000 a week (roughly the number it takes to walk 20 miles) suffered only half the annual mortality of the couch potatoes, thanks mainly to a lower rate of heart disease. Subsequent studies have shown that different activities bring different rewards. Everyone now agrees that aerobic exercise preserves the heart, lungs and brain, and researchers at Tufts University have recently shown that weight lifting can do as much for the frail elderly as it does for high school jocks. When Dr. Maria Fiatarone got 10 chronically ill nursing-home residents to lift weights three times a week for two months, the participants' average walking speed nearly tripled, and their balance improved by half. EATING TO NOURISH LONG LIFE We all know that living on fat, salt and empty calories can have a range of nasty consequences, from obesity and impotence to hypertension and heart disease. Yet there are other ways to eat, and people who adopt them stay younger longer. In controlled studies, San Francisco cardiologist Dean Ornish has shown that a diet based on low-fat, nutrient-rich foods not only prevents heart disease — the Western world's leading cause of early death — but can help reverse it. And other studies suggest that dietary changes could virtually eliminate the high blood pressure that places 50 million older Americans at high risk of stroke, heart attack and kidney failure. You wouldn't know that from watching people age in the United States. Hypertension afflicts a third of all Americans in their 50s, half of those in their 60s and more than two thirds of those over 70. But preindustrial people don' t follow that pattern. Whether they happen to live in China or Africa, Alaska or the Amazon, people in primitive settings experience no change in blood pressure as they age, and the reason is fairly simple: they don't eat processed foods. Dr. Paul Whelton of Tulane University' s School of Public Health has spent the past decade tracking 15,000 indigenous Yi people in southwestern China. As long as they eat a traditional diet — rice, a little meat and a lot of fresh fruits and vegetables — these rural farmers virtually never develop hypertension. But when they migrate to nearby towns, their blood pressure starts to rise with age. What makes processed food so harmful? Salt is one key suspect. When you subsist mainly on fresh plant foods — as our ancestors did for roughly 7 million years — you get 10 times more potassium than sodium. That 10-to-one ratio is, by Eaton' s reasoning, the one our bodies are designed for. But salt is now showered on foods at every stage of processing and preparation, while potassium leaches out. As a result, most of us now consume more salt than potassium. 'Modern humans are the only mammals that do that, 'says Eaton,