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Everything You Know Is Wrong 02 ( By TIMEasia - Sep. 6. 1999 )

Then came the news that taking benign foods like vegetable and peanut oils and hydrogenating them--a process that stiffens them to make stick margarine, peanut butter and solid shortening--transforms them into substances known as trans-fatty acids, which can drive LDL and triglyceride levels through the roof. Trans-fatty acids are not technically fats, which means, astonishingly, that a food labeled fat free may be bursting with stuff that can give you heart disease. The fact that stick margarine is bad doesn't mean butter is good. Says Dr. Walter Willett, head of nutrition at the Harvard School of Public Health: "I think the healthiest solution is none of the above." The recommendation to stay away from meats and animal fats, thus, hasn't been overthrown. It's been extended slightly to encompass a substance once thought to be relatively harmless.

How about staying away from fat entirely? Bad idea. The body needs fats, in part because vitamins like A and D must be dissolved in fat to enter the body or move about within the body. What about the super-low-fat diets, advocated by people like Dr. Dean Ornish, director of the Preventive Medicine Research Institute in Sausalito, California? They seem to work but perhaps not because they're low fat; the key may be the types of foods--beans, grains, vegetables, instead of meats and cheeses--that Ornish recommends. Indeed, Mediterranean men, who get more than 30% of their calories from fat (some three times what Ornish suggests) but who eat little saturated fat, have a very low rate of heart disease.

HDL, LDL and triglycerides aren't quite the whole story either. Over the past few years, researchers have identified yet another form of fat that could rightly be labeled Bad Cholesterol II. Called lipoprotein (a), or LP(a), it behaves like LDL in the body. But because LP(a) levels have more to do with your genes than your diet, they can't easily be controlled. At best, doctors think they can use LP(a) screening to find people who should be working extra hard to reduce their other heart-attack risks.

So fat, which started out as a good thing to eat and then became a bad thing, now turns out to be a collection of very different things, some good, some bad, some neutral. It's a pattern that has been repeated for a variety of cardiovascular risk factors. It's not pretty; the tortuous progress of scientific discovery rarely is.

SALT

Researchers realized decades ago that high blood pressure is a cardiovascular danger signal. Physicians think elevated pressure strains blood vessels, causing them to tear or develop weak areas where plaque can gain a foothold. Hypertension (to use the technical term) can also force small blood vessels to burst; if that happens in the brain, it's called a stroke--the other major cardiovascular killer besides heart attack.

Medication can help with severe cases of hypertension, but the first line of defense, physicians agree, is to cut back on a substance that has been shown to keep blood pressure high: sodium, especially in the form of salt.

If cutting back on salt is good for people with hypertension, it should logically be good for everyone else too. It may be, but dueling studies released three years ago demonstrate that the case is far from airtight. Scientists writing in the British Medical Journal concluded that reducing salt intake reduces blood pressure in all people, even those who are not hypertensive. But a study published the very same week in the Journal of the American Medical Association argued that people with normal blood pressure got no significant benefit from salt reduction.

Which one was right? Probably neither, since both studies were flawed. The J.A.M.A. study included subjects who were on low-salt diets for a very short time--perhaps too short for any effect to be noticed. And the BMJ study could not effectively measure the influence of other factors that could have made a difference. Those who ate less salt may also have watched what they ate in general, for example, exercised more or been less overweight.

The truth is that the question of what ordinary people should do about salt has simply not been settled yet. That doesn't mean we should throw up our hands in despair. Even without hard scientific proof, says Dr. Theodore Kotchen of the Medical College of Wisconsin, keeping sodium levels down is probably a good idea--particularly since there is no evidence that a low-sodium diet is harmful. The one exception: people who are losing salt through heavy perspiration during exercise or hard physical work. Reducing salt intake in the middle of a heat wave can actually be dangerous to your health.

EXERCISE

Physical exertion is another area in which doctors have been sending mixed signals. As far back as 1953, studies showed that people who got more exercise had fewer heart attacks. The physiological explanation has come more slowly, but one reason is simply that the heart is a muscle; frequent workouts keep it strong.

Another factor, doctors believe, is that exercise holds down blood pressure. When the heart pumps blood more quickly through the body, vessels dilate--or widen--to accommodate the extra flow. The overall effect is to lower pressure throughout the cardiovascular system. People who get regular exercise have about a 30% lower risk of developing heart-threatening hypertension than people who don't.

Some studies have also shown that exercise raises HDL levels; that it increases the volume of plasma (blood's liquid portion), 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 reassuring report declaring that moderate exercise was perfectly 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 U.S. 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."

VITAMIN E

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 is vitamin E, 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.

That doesn't mean, however, that popping vitamin E pills will stave off heart disease. Previous research had reached a split decision over whether supplementary E could guard against cardiovascular problems. But the study on postmenopausal women concluded that the vitamin was protective only when eaten in foods; in pill form, it didn't seem to do much good at all. This result could mean that the vitamin works in tandem with some other, as yet unidentified, food-borne substance.



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