Rather than being protective against colon cancer, as previously thought, soluble dietary fiber may actually increase the risk of adenomas, which are a type of polyp that are most likely to become cancerous.
The fiber used in the study was from ispaghula husk, which is very similar to psyllium, a fiber derived from plant husks that is found in many bulk laxatives.
The authors note that their results should not discourage people from eating a diet rich in plant foods, since these foods have been shown to lower the risk of many other disorders such as heart disease and other forms of cancer. Most plant foods are also rich in fiber, which is optimal for your body. In fact, I recommend getting about 50 grams of fiber per 1,000 calories.
Researchers studied 665 patients from 10 countries who were already at high-risk of cancer because they had polyps in their colon.
Study participants were given either:
- 3.5 grams of ispaghula husk fiber
- 2 grams of calcium in supplement form
After 3 years, patients had a colonoscopy -- a procedure in which a doctor examines the inside of the colon for growths.
The fiber supplemented group had a 67% increased risk of having at least one adenoma developed during the 3-year period in comparison with the control group.
Patients in the calcium group had a 34% decreased risk.
"Our study...suggests that low-fat, high-fiber diet...may not be effective strategies for the prevention of colorectal adenoma recurrence," Dr. Claire Bonithon-Kopp, the study's lead author, and colleagues conclude.
In an accompanying editorial, Dr. Bernard Levin from M.D. Anderson Cancer Center in Houston, Texas points to the need to find more effective therapies for colorectal adenomas. He notes that worldwide about 875,000 of colorectal cancer are diagnosed annually, accounting for approximately 8.5% of all new cancer cases. In addition, it is the second most common cause of cancer deaths in the USA and the fourth most commonly occurring cancer.
According to Dr. Levin, " ... it seems likely from this report and other recent trials that supplementation with dietary fiber is not of benefit in preventing recurrence of colorectal adenoma."
This is an important article as it really challenges some basic foundational concepts. I have reviewed it carefully with Dr. Brasco, who is a naturally oriented board-certified gastroenetrologist.
We both can not find any flaws in this study's methods. But there are some concerns with the conclusions. It is important to note that the study was not for colon cancer, but for adenomas in the colon. Although they are similar they are not the same.
The second issue is that the numerous epidemiological that provide support for the use of fiber in colon cancer prevention can not be easily dismissed. Thirdly, the fiber used in this study was a water soluble fiber and may not provide similar benefits as water insoluble fibers.
However three other studies in the past year are coming to the conclusion that adding fiber to the diet does not appear to provide protection against colon cancer.
However, the most likely reason for the discrepancy has to do with the bacterial flora content of the colon. The fiber in the diet probably favorably influences the promotion of beneficial bacteria. But if the individuals do not have large percentages of good bacteria then they would not likely receive the benefit.
One way this could be checked would be to measure butyrate levels in the stool which would be a marker for levels of beneficial bacteria.
So, just like the addition of other supplements, the KEY message is that it not the supplements, it's the whole unprocessed food that is the key to health.