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Some studies have also shown that exercise raises HDL levels; that it increases the volume of plasma (blood's liquid component), thinning the blood and thus keeping dangerous clots at a minimum; and that it may boost levels of an enzyme that vacuums cholesterol and fatty acids from the blood.
None of these results is definitive, but it seems clear that however exercise works, its benefits increase if you do more of it. That's obviously true if your goal is to stay trim; exertion is fueled by calorie burning. But plenty of studies have shown it applies to staving off heart disease too, and for years the standard medical advice was to get a minimum of 20 to 30 min. of vigorous, continuous exercise at least three times each week.
Yet in the mid-1990s, the Centers for Disease Control and Prevention and the American College of Sports Medicine published a report declaring that moderate exercise was just fine--anything from washing the car for an hour to gardening for 45 min. to raking leaves to taking a leisurely stroll around the block. And it didn't even have to be all in one shot. Three short walks, for example, could substitute for one longer one. Since then, the Surgeon General, the National Institutes of Health and the President's Council on Physical Fitness and Sports have all come out with similar guidelines.
Another example of new research refining old ideas? Not this time. The change had less to do with medicine than with marketing. "Our concern," explains Russell Pate, an exercise physiologist at the University of South Carolina and lead author of the CDC report, "was that a very large percentage of the adult population was not meeting the existing standard." Reasoning that the guidelines were just too intimidating for most people and that a little exercise had to be better than none at all, Pate and his colleagues decided to lighten up the message. "The recommendations do not say," he emphasizes, "that vigorous activity was inappropriate or that the more traditional exercise prescription model was wrong."
The processes that allow the body to turn food and air into nourishment for individual cells also create by-products that amount to toxic wastes--highly reactive oxygen molecules known as free radicals that can combine with otherwise innocent substances and transform them into killers. Free radicals may be responsible in part for the genetic damage that leads to some cancers. And they also appear to be what makes LDL and triglycerides so dangerous. When a free radical combines with one of these fatty molecules, the altered cholesterol turns into a biochemical cannonball that ricochets around the bloodstream, damaging the inner walls of vessels.
Fortunately, nature has also created chemicals known as antioxidants, which can prevent dangerous oxidation from happening in the first place. Among the most powerful of these is vitamin E, which is found in vegetable oils and nuts. In 1996 a major study of postmenopausal women showed that those who eat a diet rich in vitamin E had a 62% lower than average risk of dying from heart disease.