High Fiber/Low Fat Doesn't Cut Cancer Risk,|
2 Studies Find...
BOSTON GLOBE (By Richard Saltus, Globe Staff)
(04-20-2000: BOSTON, MA:) – If you've been wolfing down a pile of high-fiber bran flakes or other cereal every day in hopes of avoiding colon cancer, researchers have two words for you: Never mind.
A pair of studies being reported today found no benefit of a low-fat, high-fiber diet in preventing precancerous growths called polyps that sometimes are forerunners of colon cancer.
Researchers said they were surprised and disappointed to find no evidence supporting the long-held notion that such diets can reduce the risk of colon cancer, the second leading cause of cancer deaths.
The studies recruited patients who were at higher than normal risk for colon cancer because of already having had an intestinal polyp removed. Results showed that the supposedly protective diet failed to reduce their risk of having another polyp develop in their colons.
One caveat: The researchers followed the volunteers for three or four years, and it may be necessary to adhere to such a diet for a longer time to show an effect.
Also, the scientists don't recommend shunning dietary fiber and start gorging on burgers and fries. The researchers emphasize that fiber does help reduce risks of heart disease, and eating more fruits and vegetables and cutting back on fat is associated with better health.
''This doesn't mean you should throw away your bran flakes,'' said Walter Willett, a Harvard School of Public Health epidemiologist. The notion that a high-fiber diet reduced colon cancer risk stems from observations that people in developing African countries eat more grains and fruits than in the West and have little colon cancer.
The idea that fiber itself was protective, by absorbing cancer-causing substances in the bowel or by hastening their excretion, was ''compelling and simple'' but apparently wrong, said Willett. He was not involved in today's studies, but was an author on a report with similar findings last year.
The reports in today's issue of the New England Journal of Medicine are from the Polyp Prevention Trial Study Group headed by Dr. Arthur Schatzkin of the National Cancer Institute and the Wheat Bran Fiber Study led by Dr. David S. Alberts at the Arizona Cancer Center.
Colon and rectal cancer strikes about 130,000 Americans annually and causes 56,500 deaths. The disease begins as abnormal cells in the large intestine's wall that develop into polyps; about 5 to 10 percent of polyps become cancerous.
The trials reported today are the biggest to date in which volunteers were randomly assigned to follow a low-fat, high-fiber diet or to eat their usual range of foods.
In the Polyp Prevention Trial, 2,079 men and women averaging 61 years old at the start of the study were randomized into a diet group and a control group. The subjects had all had a colon polyp recently removed. The diet group had intensive counseling on achieving the goal of eating only 20 percent of calories from fat, and 18 grams of fiber and 31/2 servings of fruits and vegetables for every 1,000 calories.
All the volunteers underwent colonoscopies one and four years after the study began. At the end of the trial, there was virtually no difference in the number of people who developed recurrent polyps and those who didn't. ''It's fair to say I'm disappointed,'' said Schatzkin. ''We carried out the trial because we thought it had a real good chance of showing a difference.''
Dr. Steven Zeisel, a professor of nutrition at University of North Carolina School of Medicine, said the study's short follow-up time limits its strength. Cancer development is a long process, he said, and ''the key events may have occurred before the dietary change was made, and it was too late to do anything about it.''
Although advertisements for high-fiber breakfast cereals have created the impression they could prevent colon cancer, the actual labeling on the products approved by the Food and Drug Administration is unlikely to change.
A spokeswoman for Kellogg's said the current labeling says: ''Low-fat diets rich in fiber-containing grain products, fruits and vegetables may reduce the risk of certain cancers.''
Dr. Tim Byers of the University of Colorado School of Medicine said in a Journal editorial that there are many reasons to eat low-fat, high-fiber diets, ''but preventing colorectal adenomas,'' or polyps, ''is not one of them.''