Study confirms link between diet and colon cancer


December 18, 1990|By Gerri Kobren

Astudy that last week showed a link between colon cancer and red meat confirmed what health experts have been saying for years: It's best to limit how often you eat meat and how much you eat when you do.

"One of the most important things about the study is that it comes after a lot of other evidence," said Dr. Walter C. Willett, professor of epidemiology and nutrition at the Harvard School of Public Health.

Dr. Willett, director of the six-year study of the dietary habits of 88,751 nurses, found that those who ate beef, lamb or pork every day had 2 1/2 times the risk of colon cancer as those who ate red meat once a month or less. Women who ate skinless chicken or fish instead of red meat had a much lower risk than their meat-eating colleagues.

The study was published in the New England Journal of Medicine.

"This is a strong confirmatory finding, and given the importance of colon cancer in this country and the additional likely benefits from the standpoint of heart disease, it seems reasonable to cut back to once or twice a week and have relatively small amounts," Dr. Willett said in a phone interview last week. "It may also be reasonable to give it up entirely," he added.

Colon cancer, the second leading cause of cancer death (after lung cancer) in the nation, will strike about 110,000 Americans in 1990, according to American Cancer Society projections. Among the risk factors are family history, inflammatory bowel disease and high-fat, low-fiber diets.

In fact, health experts have advised lower-fat diets for years, based on studies that show colon cancer is more frequent in the meat-eating United States than in Asian and African countries where diets are based more on grains and vegetables.

The "best guess" about why the study showed an association between risk and red meat is its fat content, Dr. Willett said. To digest fat, the liver sends a lot of bile into the colon where bacteria can make it carcinogenic. Skinless chicken and fish, which are less fatty, do not have that bile-increasing effect.

"What this study does is clearly demonstrate what everyone has been thinking for a long time: that fat intake is related to the risk of colon cancer," said Dr. Jonathan Schreiber, a gastroenterologist who directs clinical services in gastro-intestinal disease at University of Maryland Hospital.

But while Dr. Schreiber believes that reducing dietary fat is beneficial, he does not tell people how much or how little meat they should eat.

The study's results, he pointed out, emphasized extremes by comparing people who ate meat every day with those who ate it less than once a month. Most people, however, have food habits that fall somewhere in between, and the best advice, therefore, is couched in relative terms.

"What people should do is try to eat as little fat as they can; it would certainly be to their benefit to cut down as low as they can get," he said.

Dr. Schreiber also advises people to increase their fiber intake from all sources, though he noted that Dr. Willett's study showed that only the fiber in fruit, and not the kind in vegetables and cereals, seemed associated with a decreased risk. Dr. Willett himself suggests that people follow current national dietary guidelines, which call for five servings of fruit and vegetables a day.

Neither Dr. Schreiber nor Dr. Willett is worried about nutritional adequacy on a meat-free diet. "One of the issues that's been raised is related to dietary iron," Dr. Willett said. "I think one should always be concerned about having a balanced diet, but one can easily do that without red meat if you're eating chicken and fish. In terms of iron, there are other good sources, including most greens, soybeans and other types of beans, and most fortified bread, flour and cold cereals."

Richard Ahrens, professor of nutrition and coordinator of the graduate program in nutritional sciences at the University of Maryland College Park, agreed that people can get along without meat. Vegetarians, he noted, "can do OK if they eat wisely -- though many are recommended to take an iron supplement."

However, he added, red meat is a better source of dietary iron than chicken, fish or vegetables. And though the fat in meat might be a problem, there's a trend now to leaner meat. "That gets you a good source of protein and iron without a lot of extra fat," he said. "I don't think you can make a blanket condemnation of all red meat from a nutritional standpoint."

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