I DON'T USUALLY FOLLOW nutrition stories, but it was hard to miss last week's shocker about low-fat diets. Like many papers, The Boston Globe put it on Page 1, high above the fold: "Study finds no major benefits of low-fat diet." The study, a project of the National Institutes of Health, had taken eight years, cost $415 million, and involved nearly 49,000 older women, 40 percent of whom were assigned to a diet that kept their intake of calories from fat significantly below that of the other 60 percent. Researchers had expected to confirm what earlier studies and conventional medical wisdom had long suggested -- that consuming less fat is good for your health.
What they learned instead was that the women who dutifully cut back on fried foods, ice cream, and pizza ended up no better off than the women who ate whatever they wanted. The two groups developed breast cancer, colon cancer, heart attacks, and strokes at the same rates. Millions of Americans have been trying for years to reduce the fat in their diet -- eating bread without butter, salads without dressing, chicken without skin -- and now the largest study of the subject ever conducted says it has all been for naught. You could have had those fries after all.
And so once again we are reminded, as The New York Times sighed in an editorial on Thursday, that "the more we learn about nutrition, the less we seem to know." Does oat bran reduce cholesterol? Can dietary fiber prevent colon cancer? Are high doses of Vitamin E good for your heart? Once, the experts said yes. Then the experts said no. It sometimes seems that for every study that makes a nutritional claim, another study inevitably makes an equal and opposite claim.
Researchers can't even agree on whether eating less fat is the way to lose weight. Some insist that obesity is caused by ingesting too much fat, making a low-fat diet the key to shedding pounds. Others claim that reducing fat leads to overconsumption of carbohydrates -- and that it's carbs, not fat, that make people gain weight. Which theory did the massive new study confirm? Neither. Apparently there is still no clear-cut answer -- not even for $415 million.
But clear-cut answers are just what so many Americans want, and what so many of them think science ought to be able to provide. There is a seemingly inexhaustible willingness to believe that the voice of science is the voice of truth -- impartial, incorruptible, and unambiguous. It isn't, of course. Scientists are no less vulnerable to error or bias or ego than the rest of the human race. Scientists too can blunder or act from ulterior motives or convince themselves of things that aren't so. And yet on the whole they enjoy a level of deference and public trust that people in most other fields can only envy.
Which is probably not a good thing. Scientific pronouncements should be subjected to the same level of healthy skepticism as the promises of politicians or the claims of advertisers -- or the views of newspaper columnists. With the best of intentions (and otherwise), scientists sometimes peddle claptrap. Just because a statement begins with "A new study shows . . ." or "Researchers have found . . ." doesn't mean that what follows is true. "We in the scientific community often give strong advice based on flimsy evidence," Berkeley statistician David Freedman said last week in a comment on the low-fat diet study. "That's why we have to do experiments." And why the rest of us have to remember that contradiction, confusion, and changing opinions have always been a part of the scientific process.
One day after last week's low-fat story, the New England Journal of Medicine was out with a study concluding that saw palmetto extract, an herbal product, has no effect on the symptoms caused by an enlarged prostate. Earlier studies had found just the opposite, and more than 2 million American men take saw palmetto for their prostate condition. So does it work or doesn't it? Whichever answer you choose, there's a study to back it up.
In Newsweek last month, Dr. Harvey Simon of the Harvard Medical School recanted a view he had preached for years: that the only way to benefit from exercise was through intense aerobic activity, complete with pounding heart and rivers of sweat. Now, citing the latest research, he says he was dead wrong, and that gentle, no-sweat exercise -- even walking or gardening -- is also highly effective.
From cardiac health to climate change, it's worth keeping in mind that what the experts say today they may not be saying tomorrow. As that noted scientist Emily Litella used to put it in the old "Saturday Night Live" skits: Never mind.
(Jeff Jacoby is a columnist for The Boston Globe).
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