010654 Study Focuses on Red Meat, Cancer

New research indicates that eating lots of red meat may create about as much of a certain cancer-promoting chemical in the colon as smoking does.

The findings, presented Lyon at the European Conference on Nutrition and Cancer, were part of a study that also appears to revive the theory that fiber wards off colon cancer, the second most deadly cancer worldwide.

The idea that a high-fiber diet rich in fruits, vegetables and grains prevents colon cancer suffered a setback last year after two studies failed to find an effect.

But the latest research, which experts say is the most reliable to date on the link between eating habits and cancer, found that those who ate a high-fiber diet had 40% less chance of developing colon cancer than those who ate the least roughage.

The study, which involved 406,323 people from nine European countries, had the widest range in fiber intake of any study to date.

At the start of the study, in 1993, questionnaires separated the people into five categories, according to how much fiber they ate. The top and bottom 1% were excluded to eliminate extremes. There were about 80,000 people in each of the remaining categories.

There were 176 colon cancer diagnoses in the group who ate the least fiber and 124 cases in the group that ate the most - a difference of 40%.

The finding redeems fiber as a potential anti-cancer agent, said Nicholas Day, a cancer expert at Cambridge University in England. Day was not involved in the fiber investigation.

Day has criticized previous studies on nutrition and cancer. He says they were too small, were limited to one country at a time, included narrow ranges in eating patterns and did not measure precisely enough to detect the effect of small differences in nutrition.

Dr. Anthony Miller, a professor at the German Cancer Research Center who was not involved in the study, agreed.

“I think this study shows things are beginning to come together,” Miller said. “The (American) studies, the way they measured everything was not very good.”

Scientists believe that bacteria in the colon ferment fiber and in the process create a by-product called butyrate. Experts believe that cells in the lining of the colon turn cancerous when normal cell death is hampered. Test-tube studies have shown that butyrate is a potent inducer of cell death.

Those who don't eat a lot of fiber tend to load up on protein, which also provides food for bacteria in the colon, said Dr. Sheila Bingham, deputy director of the Human Nutrition Unit at Cambridge University, who led both studies.

Lab tests have shown that the combination of red meat and colon bacteria produces chemicals called N-Nitroso compounds, some of which are cancerous, Bingham said.

One of them, known as NNK, is found in tobacco smoke.

In the meat experiment, volunteers moved into a laboratory for at least three months and their diets were manipulated. Cells from the lining of the colon that were shed during defecation were examined to see the effect of the dietary changes.

Everyone was put on the same regime. Calories, fat and weight were kept the same throughout, but the amounts and types of protein changed.

The more red meat eaten, the higher the concentration of N-Nitroso in the feces.

“In fact, at the high level of red meat consumption, the level of N-Nitroso compounds which were present in the fecal material was equivalent to the concentration that is found in tobacco smoke,” Bingham said.

The most red meat the scientists gave the volunteers was 420 grams (15 ounces) per day.

Replacing the red meat with the same amount of chicken or fish resulted in a drop in the N-Nitroso compounds back to normal. They stayed at that level when the protein came from dairy or soy products.

“The only difference between red and white meat is the amount of heam they contain,” Bingham said. Red meat is rich in heam, a part of the blood that contains the iron that gives the meat its red color.

When the volunteers were fed a diet low in red meat but with supplements of heam iron, the levels of N-Nitroso in the feces rose again.

Experts say the results are consistent with other evidence presented at the meeting Friday, which indicated that preserved meats increase the risk of colon cancer, but that fresh red meat may not.

Preserved meat, which includes bacon, cured ham, salami, corned beef and pastrami, has much more heam than fresh meat such as steak or lamb chops.

There is no proof that N-Nitroso compounds in the colon are toxic, but the circumstantial evidence is strong that it might be, experts said.

“Some of these compounds are very carcinogenic ... in other species, and humans have the same enzymes which are required to metabolize them, so really it's a logical thing,” Day said.

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