||Miércoles 15 de Febrero de 2006, Ip nº 140
|Maybe You're Not What You Eat
Por GINA KOLATA
In an early 19th-century best seller, a famous food writer offered a cure for obesity and chronic disease: a low-carbohydrate diet.
The notion that what you eat shapes your medical fate has exerted a strong pull throughout history. And its appeal continues to this day, medical historians and researchers say.
"It's one of the great principles — no, more than principles, canons — of American culture to suggest that what you eat affects your health," says James Morone, a professor of political science at Brown University.
"It's this idea that you control your own destiny and that it's never too late to reinvent yourself," he said. "Vice gets punished and virtue gets rewarded. If you eat or drink or inhale the wrong things you get sick. If not, you get healthy."
That very American canon, he and others say, may in part explain the criticism and disbelief that last week greeted a report that a low-fat diet might not prevent breast cancer, colon cancer or heart disease, after all.
The report, from a huge federal study called the Women's Health Initiative, raises important questions about how much even the most highly motivated people can change their eating habits and whether the relatively small changes that they can make really have a substantial effect on health.
The study, of nearly 49,000 women who were randomly assigned to follow a low-fat diet or not, found that the diet did not make a significant difference in development of the two cancers or heart disease. But there were limitations to the findings: the women assigned to the low-fat diet, despite extensive and expensive counseling, never reached their goal of eating 20 percent fat in the first year —only 31 percent of them got their dietary fat that low. And the study did not examine the effects of different types of fat — a fact that critics say is a weakness at a time when doctors are advising heart patients to reduce saturated fat in the diet, not overall fats.
The researchers also found a slight suggestion that low fat might make a difference in breast cancer but the results were not statistically significant, meaning they may have occurred by chance.
Still the study's results frustrate our primal urge to control our destinies by controlling what we put in our mouths. And when it comes to this urge, it is remarkable how history repeats itself. Over and over again, medical experts and self-styled medical experts have insisted that one diet or another can prevent disease, cure chronic illness and ensure health and longevity. And woe unto those who ignore such dietary precepts.
For example, Jean Anthelme Brillat-Savarin, the French 19th-century food writer, insisted that the secret to good health was to avoid carbohydrates. Brillat-Savarin, a lawyer, also knew the response his advice would provoke.
" 'Oh Heavens!' all you readers of both sexes will cry out, 'oh Heavens above!" he wrote in his 1825 book, "The Physiology of Taste." "But what a wretch the Professor is! Here in a single word he forbids us everything we must love, those little white rolls from Limet, and Achard's cakes and those cookies, and a hundred things made with flour and butter, with flour and sugar, with flour and sugar and eggs!"
Brillat-Savarin continued, "He doesn't even leave us potatoes or macaroni! Who would have thought this of a lover of good food who seemed so pleasant?
" 'What's this I hear?' I exclaim, putting on my severest face, which I do perhaps once a year. 'Very well then; eat! Get fat! Become ugly and thick, and asthmatic, finally die in your own melted grease."
The Frenchman's recipe for good health was only one of many to come. A decade later, the Rev. Sylvester Graham exhorted Americans to eat simple foods like grains and vegetables and to drink water.
Beef and pork, salt and pepper, spices, tea and coffee, alcohol, he advised, all lead to gluttony. Bread should be unleavened, and made with bran to avoid the problem of yeast, which turns sugar into alcohol, he continued. It is also important, he said, to seek out fresh organic fruits and vegetables, grown in soil without fertilizers.
The reward for living right, Graham promised, would be perfect health.
A few decades later came Horace Fletcher, a wealthy American businessman who invented his diet in 1889. He was 40 and in despair: he was fat, his health was failing, he was always tired and he had indigestion. He felt, he said, like "a thing fit but to be thrown on the scrap-heap."
But Fletcher found a method that, he wrote, saved his life: eat only when you are hungry; eat only those foods that your appetite is craving; stop when you are no longer hungry and, the dictum for which he was most famous, chew every morsel of food until there is no more taste to be extracted from it.
Fletcher became known as the Great Masticator, and his followers recited and followed his instructions to chew their food 100 times a minute. Liquids, too, had to be chewed, he insisted. He promised that "Fletcherizing," as it became known, would turn "a pitiable glutton into an intelligent epicurean."
Along with the endless chewing, Fletcher and his supporters also advocated a low-protein diet as a means to health and well-being.
But by 1919, when Fletcher, 68, died of a heart attack, his diet plan was on its way out, supplanted by the next new thing: counting calories. Its champions were two Yale professors, Irving Fisher and Eugene Lyman Fisk, who wrote the best-selling book "How to Live."
"Constant vigilance is necessary, yet it is worthwhile when one considers the inconvenience as well as the menace of obesity," Fisher and Fisk advised their readers.
More recently, of course, the preferred diet, at least for cancer prevention, has been to eat foods low in fat. And that was what led to the Women's Health Initiative, a study financed by the National Institutes of Health comparing low fat to regular diets.
Eight years later, the women who reduced dietary fat had the same rates of colon cancer, breast cancer and heart disease as those whose diets were unchanged.
They also weighed about the same and had no difference in diabetes rates, or in levels of insulin or blood sugar.
It made sense to try the low-fat diet for cancer prevention, said Dr. Elizabeth Nabel, the director of the Women's Health Initiative.
"In the mid- to late 1980's, there was a body of literature that was suggestive that diet might impact the incidence of breast cancer and colorectal cancer," Dr. Nabel said.
For example, studies found that women acquired a higher risk of those cancers if they moved to the United States from countries where incidence of the cancers was low and where diets were low in fat.
And there were animal studies indicating that a high-fat diet could lead to more mammary cancer.
But intriguing as those observations were, there was no direct, rigorous evidence that a low-fat diet was protective.
The Women's Health Initiative study would be the first rigorous test to see if it was. The study investigators decided to follow heart disease rates, as well.
"Think of it," said Dr. Joan McGowan, an osteoporosis expert who is also a project officer for the Women's Health Initiative. "Here was a hypothesis that just a better diet could prevent breast cancer. How attractive was that?"
In the meantime, the notion that fat was bad and that low-fat diets could protect against disease took hold, with scientists promoting it and much of the public believing it. And a low-fat food industry grew apace.
In 2005, according to the NPD Group, which tracks food trends, 75 percent of Americans said they substituted a low-fat or no-fat food for a higher-fat one once a week or more.
So last week, when the study's results, published in The Journal of the American Medical Association, showed that the low-fat diets had no effect, the study investigators braced themselves for attacks.
Dr. Jacques Rossouw, the project officer for the Women's Health Initiative, said the researchers knew that some critics would say the women did not reduce the fat in their diets nearly enough. Perhaps a lower-fat diet would have offered some protection against cancer, Dr. Rossouw said. But, he said, "what we achieved is probably what was achievable."
Other critics said that the study made a mistake in even aiming for 20 percent of calories as fat. Dietary fat should be even lower, they said, as low as 10 percent.
But Dr. Rossouw said this was unrealistic, because try as they might, people are not able to change their eating habits that much.
"You can't do that," he said. "Forget it. It's impossible."
Critics now are telling the investigators that the study was useless because it focused on total fat in the diet, rather than on saturated fat, which raises cholesterol levels. If the women had focused instead on getting rid of fats like butter, had substituted fats like olive oil and had eaten more fruits and grains, then the study might have shown that the proper diet reduces heart disease risk, they claim.
"Lifestyle goes beyond a modest difference in saturated fat," said Dr. Robert H. Eckel, president of the American Heart Association.
Dr. Rossouw responded, "They're telling us that we chose the wrong kind of fat and that we just didn't know."
But, he said: "We're not stupid. We knew all that stuff."
The investigators, he said, had long debates about whether to ask the women to reduce total fat or just saturated fat.
In the end, they decided to go with total fat because the study was primarily a cancer study and the cancer data were for total fat.
If the women had reduced just their saturated fat, their dietary fat content would probably have been even higher, fueling the critics. And, he said, some animal data indicate that polyunsaturated fat may even increase cancer risk.
"We looked at all possible scenarios," Dr. Rossouw said. But, he said, given the study's disappointing findings, he was not surprised by the critics' responses.
Not everyone is attacking the study. Many scientists applaud its findings and say it is about time that some cherished dietary notions are put to a rigorous test. And some nonscientists are shocked by the reactions of the study's critics.
"Whatever is happening to evidence-based treatment?" Dr. Arthur Yeager, a retired dentist in Edison, N.J., wrote in an e-mail message. "When the facts contravene conventional wisdom, go with the anecdotes?"
The problem, some medical scientists said, is that many people — researchers included — get so wedded to their beliefs about diet and disease that they will not accept rigorous evidence that contradicts it.
"Now it's almost a political sort of thing," said Dr. Jules Hirsch, physician in chief emeritus at Rockefeller University. "We're all supposed to be lean and eat certain things."
And so the notion of a healthful diet, he said, has become more than just a question for scientific inquiry.
"It is woven into cultural notions of ourselves and our behavior," he said. "This is the burden you get going into a discussion, and this is why we get so shocked by this evidence."
The truth, said Dr. David Altshuler, an endocrinologist and geneticist at Massachusetts General Hospital, is that while the Western diet and lifestyle are clearly important risk factors for chronic disease, tweaking diet in one way or another — a bit less fat or a few more vegetables — may not, based on studies like the Women's Health Initiative, have major effects on health. "We should limit strong advice to where randomized trials have proven a benefit of lifestyle modification," Dr. Altshuler wrote in an e-mail message.
Still, he said, he understands the appeal of dietary prescriptions.
The promise of achieving better health through diet can be so alluring that even scientists and statisticians who know all about clinical trial data say they sometimes find themselves suspending disbelief when it comes to diet and disease.
"I fall for it, too," says Brad Efron, a Stanford statistician. "I really don't believe in the low-fat thing, but I find myself doing it anyway."
|| 14/02/2006. The New York Times.