Archives - Biology: Page 31
Author: paul carson (Mon Dec 12, 2005 7:17 pm)
Title: The Fiber Theory
The Fiber Theory
The research results of a careful longitudinal diet study of two groups of individuals that follow the same diet (one fiber dependent and one not) for a number of years to prove the possible benefits of the fiber theory ( as a factor to avoid breast and colon cancer) wasn't very encouraging, in fact many researchers say they were taken aback. The findings, they said, were not what they expected.
Fat in the diet, the studies found, made no difference for breast cancer. "For fat and breast cancer, almost all of the prospective studies were null," Dr. Schatzkin said.
Fiber, in the form of fruits and vegetables, seemed to have a weak effect or no effect on colon cancer.
The more definitive randomized controlled trials were disappointing, too, with one exception. A study reported in May found that women with early stage breast cancer who followed a low-fat diet had a 20 percent lower risk of recurrence.
Even so, the effects were just marginally statistically significant. The study's principal investigator, Dr. Rowan Chlebowski of the Harbor-U.C.L.A. Medical Center, said it needed to be repeated before scientists would be convinced.
Nonetheless, the study contrasted sharply with those preceding it. Several involved beta carotene and antioxidant vitamins like C and E, substances that scientists thought were the protective agent in fruits and vegetables. The idea was that antioxidants could mop up free radicals in the body, which left unchecked could damage DNA, causing cancer.
Beta carotene was of special interest. People who ate lots of fruits and vegetables had more beta carotene in their blood, and the more beta carotene in the blood, the lower the cancer risk.
But a four-year study that asked whether beta carotene, with or without vitamins C and E, could protect against colon polyps, from which most colon cancers start, found no effect. People who took either beta carotene, vitamin C, vitamin E or all three had virtually identical rates of new polyps compared to participants taking dummy pills.
Another study, of 22,000 doctors randomly assigned to take beta carotene or a placebo, looked for an effect on any and all cancers. It found nothing. Two more, involving current and former smokers, found that those taking beta carotene actually had slightly higher lung cancer rates than those taking placebos.
Studies of fiber and colon cancer were similarly disappointing.
The fiber hypothesis had enormous appeal. Carcinogens from food can end up in stool. But when people eat a lot of fiber, their stool is bulkier and so carcinogens would be diluted. Bulkier stool is also excreted faster, reducing the time that the colon is in contact with cancer-causing substances.
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