Studies revive theory that high-fiber diet may prevent colon cancer
Thursday, May 1st 2003, 12:00 am
News On 6
LONDON (AP) _ New research has revived the notion that a high-fiber diet may protect against colon cancer.
Long-standing recommendations for high-fiber diets have taken a hit over the last few years after a handful of carefully conducted studies failed to find a benefit.
But experts say two major studies published this week in The Lancet medical journal _ one on Americans and the other on Europeans _ indicate previous research may not have examined a broad enough range of fiber consumption or a wide enough variety of fiber sources to show an effect.
``These two new findings show that the fiber hypothesis is still alive,'' said the leader of the American study, Ulrike Peters of the U.S. National Cancer Institute.
Figuring out the relationship between nutrition and disease has always proved difficult, but experts say fiber is particularly complicated because there are various types and they all could act differently.
Fiber is found in fruits, vegetables and whole grains. Americans eat about 16 grams a day, while Europeans eat about 22 grams. The new studies indicate fiber intake needs to be about 30 grams a day to protect against colon cancer.
There are 2 grams of fiber in a slice of whole meal bread. A banana has 3 grams and an apple has 3.5 grams, the same as a cup of brown rice. Some super-high fiber breakfast cereals have as much as 14 grams per half cup.
In the American study, investigators compared the daily fiber intake of 3,600 people who had precancerous growths in the colon with that of around 34,000 people who did not.
They were divided into five groups, according to how much fiber they ate. The average roughage intake in the lowest group was 12 grams a day, while in the highest group it was 36 grams a day.
People who ate the most fiber had a 27 percent lower risk of precancerous growths than those who ate the least.
In the European study, the largest one ever conducted on nutrition and cancer, scientists examined the link in more than 500,000 people in 10 countries.
As in the American study, questionnaires separated the people into five groups, according to fiber intake.
Following them for an average of four years, 1,065 of them had developed colorectal cancer.
Those who ate the most fiber, about 35 grams a day, had about a 40 percent lower risk of colorectal cancer compared with those who ate the least, about 15 grams a day, the study found.
``In the top quintile (group) they were eating 15 grams of cereal fiber, which is equivalent to five or six slices of whole meal bread, plus they were eating seven portions of fruit and vegetables a day, which is basically the Mediterranean levels,'' said the study's leader, Sheila Bingham, head of the diet and cancer group at Cambridge University's human nutrition unit.
Discussions about the link between fiber and bowel health _ or, at least the relative merits of white and brown bread _ date back to antiquity.
In a twist on modern thought, Hippocrates, who lived in the 5th century B.C., believed white bread was more nutritious because it creates less feces than brown bread. Scientists now believe the extra feces is a benefit.
The contemporary theory that fiber wards off colon cancer began in the 1970s, when a British doctor, Denis Burkitt, noted that poor people in Africa produce more feces than Westerners and get much less colon cancer. One obvious difference between the two groups was that Africans consumed more fiber.
Scientists believe that fiber dilutes and absorbs cancer-causing agents and makes them flow more quickly through the body. Researchers have also theorized that a high-fiber diet makes protective changes to cells or curtails bile acids that irritate the intestinal lining and promote growths.
The first big dent in the theory came in 1999 from a study that tracked the eating habits of 88,757 American nurses for 16 years. The risk of colon cancer was the same, regardless of how much fiber the women were eating.
Then in 2000, two studies which used a different method also came up negative. They put people on different diets and counted precancerous growths in their colons for up to four years. There was no apparent effect from high-fiber diets or supplements.
One major difference between the former and current studies is that the new ones examine more diverse populations who eat different types of fiber and in hugely varying amounts.
However, Andy Ness, a lecturer in epidemiology at Bristol University in England, who was not connected with either study, said the latest research is not the last word.
``Across Europe, there is an amazing variation in risks of cancer. There is also a huge variation in diet, so across these cultures you can get this breadth of intake. However, what you might be picking up across this range of diet is a range of cultures. It's possible it's something else that goes with that pattern of diet,'' he said.