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Why do constipated women appear to be at higher risk for breast cancer? The results of a 1989 study out of the American Journal of Public Health suggested a slight increased risk of breast cancer for both decreased frequency of bowel movements and firm stool consistency. Women who had three or more bowel movements a day appeared to cut their risk of breast cancer in half. This could be because constipation means a greater contact time between our waste and our intestinal wall, which may increase the formation and absorption of fecal mutagens—substances that cause DNA mutations and cancer—into our circulation, eventually ending up in breast tissue.

The concept that more frequent bowl movements decrease breast cancer risk dates back more than a century, where severe constipation, so-called “chronic intestinal stasis,” was sometimes dealt with surgically. Figuring that the colon was an inessential part of the human anatomy, why not cure constipation by just cutting it out? After the surgery, they noticed that potentially precancerous changes in the breasts of constipated women seemed to disappear.

It would take another 70 years before researchers followed up on the clues by those distinguished surgeons who claimed breast pathology cleared when constipation was corrected. A 1981 study published in The Lancet investigated the relation between potentially precancerous changes in the breast and the frequency of bowl movements in nearly 1,500 women (See Breast Cancer and Constipation). The researchers found that the risk of precancerous changes was four times greater in women reporting two or fewer bowel movements a week compared to more than once daily.

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We know that even the non-lactating breast actively takes up chemical substances from the blood. We also know that there are mutagens in feces. It is not unreasonable to suggest that potentially toxic substances derived from the colon have damaging or even carcinogenic effects upon the lining of the breast. Toxic substances like bile acids. Bile acids were first shown to promote tumors in mice in 1940, but subsequent experiments on rats led to the mistaken belief that bile acids just promoted existing cancers and couldn’t initiate tumors themselves. However, there is a fundamental difference between the rodent models and human cancer. Rats only live a few years, while humans can live dozens; so, the opportunity for cancer causing mutations may be at least 30 times greater in humans. We now have at least 15 studies that show that bile acids can damage DNA, strongly suggesting they can initiate new cancers as well.

Bile acids are formed as a way of getting rid of excess cholesterol. Our liver dumps bile acids into the intestine for disposal, assuming our intestines will be packed with fiber to trap it and flush it out of the body. But if we haven’t been eating enough fiber-rich whole plant foods, bile acids can be reabsorbed back into the body and build up in the breast.

Carcinogenic bile acids are found concentrated in the fluid of breast cysts at up to a hundred times the level found in the bloodstream. By radioactively tagging bile acids, researchers were able to show that intestinal bile acids rapidly gain access to the breast, where they can exert an estrogen-like cancer-promoting effect on breast tumor cells. This would explain why we see 50% higher bile acid levels in the bloodstream of newly diagnosed breast cancer victims. These findings support the concept of a relationship between intestinally-derived bile acids and risk of breast cancer. So, how can we facilitate the removal of bile acids from our body?

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Slowed colonic transit can increase bile acid levels. Therefore, to decrease absorption of bile acids, we can speed up the so-called “oro-anal transit time,” the speed at which food goes from mouth to toilet, by eating lots of fiber. A diet packed with plants greatly increases bile acid excretion.

Fiber can bind up and remove other toxic elements like lead and mercury as well as cholesterol and bile acids. But plants can bind bile acids even independent of fiber. Vegan diets bind significantly more bile acid than lacto-ovo or non-vegetarian diets even at the same fiber intake, which could explain why individuals eating vegetarian might excrete less mutagenic feces in the first place.

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I touched on this in my live presentation From Table to Able: Combating Disabling Diseases with Food, but what I didn’t get to discuss is the relative bile acid binding abilities of different foods. I cover that in my video Which Vegetable Binds Bile Best?

What intestinal transit time should we be shooting for? See Food Mass Transit. That may be why Stool Size Matters. Also, How Many Bowel Movements Should You Have Every Day? We can improve speed and size by Bulking Up on Antioxidants and eating lots of whole plant foods (Prunes vs. Metamucil vs. Vegan Diet).

Fiber may also help women remove excess estrogen from their body. See my video Fiber vs. Breast Cancer. For more on the wonders of fiber, see Dr. Burkitt’s F-Word Diet.

For more of my latest videos on breast cancer prevention and survival, see:

In health,
Michael Greger, M.D.

This article was republished with permission from nutritionfacts.org.

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