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Probiotics May Cut Colon Cancer Risk
Friendly bacteria linked to reduced risk; a microbe in yogurt and supplements shows promise

11/13/2017 By Michelle Lee with Craig Weatherby

Colon cancer is the third most common type in the United States.

More than 135,000 new cases occur every year, and this malignancy — also called colorectal cancer — affects men somewhat more than women.

Most colorectal cancer starts as a growth — called a polyp — some of which become cancerous, while others remain benign.

The known risk factors include some you can control, and others we can’t:

  • Smoking
  • Type-2 diabetes
  • Heavy alcohol use
  • Lack of physical activity
  • Being overweight or obese
  • Family history of CR cancer
  • Diets high in red and processed meats
  • Diets low in fiber, fruits and vegetables
  • History of polyps or inflammatory bowel diseases
  • Being age 50 or older — the risk rises every subsequent year

And encouraging findings enhance the promise of a probiotic bacteria commonly found in yogurt, other fermented foods, and probiotic supplements.

We relay its results in "Baylor study finds promise in a common probiotic bug", below — but let’s first review the basics about our gut microbes, and foods that help highly healthful bugs gain the upper hand.

What is the microbiota?
Scientists use three similar terms to refer to the microbes (bacteria, viruses, and fungi) that live in our bodies.

These terms — microbiota, microflora, and microbiome — mean roughly the same thing, although "microbiome" also encompasses the microbes’ genetic material.

Your gastrointestinal system hosts both friendly and unfriendly microbes, which are also found in our nasal membranes, saliva, and gums, and on our eyes, tongues, and skin.

People harbor from 10 to 100 trillion microbes, or 10 times the number of cells in our bodies. Because microbes are much smaller than our cells, they only constitute about three percent of our body weight.

The list of benefits associated with friendly gut bacteria has been growing fast, and we've reported on some of those findings. For example, see Live Cultures May Lift Mood, Friendly Bugs Cut Colds, Microbes Make Some Folks Fat, Do Friendly Bugs Fight Fat?, and Cultured Foods for Social Comfort.  

What are probiotics and prebiotics?
Probiotics are friendly microbes — mostly bacteria — found in supplements and in cultured foods like yogurt, kefir, and fermented vegetables.

Prebiotics are factors in plants foods that foster the growth of probiotics. Prebiotics fall into three major categories:

  • Resistant starch, which is found in barley, oats, and beans.
  • Polyphenol antioxidants, which abound in colorful vegetables and fruits, and especially the flavanols found tea, raw cocoa, and dark chocolate.
  • Fibers and complex sugars, such as oligosaccharides (e.g., FOS or inulin), pectin, and lignans. The best common food sources of these prebiotics include apples, chicory root, burdock root, jicama root, Jerusalem artichokes, dandelion greens, garlic, leeks, onions, flaxseed, wheat bran, bananas, asparagus, and seaweed.

Cooking breaks down oligosaccharides to some extent, so it’s best to cook its source foods lightly, or eat them raw. Fortunately, it’s easy to find supplements featuring prebiotic fibers.

For past reports on foods that help or hinder microbial gut health, see The Culture War in Your Gut, Cultured Foods 101, from Kimchi to Kefir, Tea May Enhance Intestinal Health and Immunity, and Cocoa and Dark Chocolate May Aid Gut Health.

The gut biome and colon cancer prevention
The American Cancer Society and others estimate that diet may trigger 30% to 50% of colorectal cancers, or possibly even more cases.

In large part, that’s because diet strongly affects the composition of the microbial colonies in our guts, which in turn affects the risk for colorectal cancers by influencing key colorectal risk factors:

  • Decreased inflammation
  • Better intestinal detoxification
  • Stronger overall immune function
  • Stronger immune function in the colon
  • Direct inhibition of tumor development
  • Improved (faster) food transit time through the gut.

And studies in which researchers manipulated the gut bacteria of mice provides very strong evidence that the composition of the human microbiota plays a powerful role in the development of colon cancer

Michigan State University researchers published two such studies in recent years, and came to these striking conclusions:

  • “… changes in the gut microbiome … directly contribute to tumorigenesis and suggest that interventions affecting the composition of the microbiome may be a strategy to prevent the development of colon cancer.” (Zackular J et al. 2013)
  • “These results further bolster the evidence that the gut microbiota is involved in mediating the development of colorectal cancer … [so] alteration of the gut microbiota may be a useful approach to preventing and altering the trajectory [hindering the growth] of colorectal cancer.” (Zackular J et al. 2015)

Findings like those are bolstered by good and growing evidence that probiotics — especially bacteria belonging to the Lactobacillus and Bifidobacteria families — can help prevent and treat inflammatory gut disorders like IBD and colitis, which are known to promote colorectal cancer.

Many population and lab studies — and a few clinical studies — have tried to determine whether and how probiotics and prebiotics might help prevent colon cancer.

So-called “cohort” studies — which examine large populations looking for links between dietary factors and disease — have produced mixed findings, with no strong links yet seen between higher probiotic intakes and lower risk of colon cancer.

However, some case-control studies — which compare cancer patients to healthy controls, and whose results can provide greater confidence — have detected protective effects from fermented milk products such as yogurt.

And some clinical studies in which people were assigned to eat fermented dairy foods detected reductions in well-known markers for risk of colorectal cancer.

Eleven years ago, the authors of an evidence review from Australia made these two observations, and the evidence supporting their conclusions has only grown stronger (Geier MS et al. 2006):

  • “There is substantial experimental evidence to suggest that probiotics and prebiotics may be beneficial in the prevention and treatment of colon cancer.”
  • “Probiotics and prebiotics act to alter the intestinal microflora by increasing concentrations of beneficial bacteria such as lactobacillus and bifidobacteria, and reducing the levels of pathogenic micro-organisms …”.

The authors of an Italian evidence review published the same year noted that the results of epidemiological studies were mixed, but concluded that, “an ample body of evidence supports the potential anticarcinogenic action of probiotics on the basis of the results obtained in both in vitro [test tube] and in vivo [animal] models.” (Capurso G et al. 2006)

A 2010 review from researchers at India's National Dairy Research Institute looked more broadly at probiotics as cancer preventers in general, beyond colorectal tumors.

The authors found no published clinical proof that probiotics treat or prevent cancer, but noted the many animal studies showing that probiotics can reduce both risky DNA damage and resulting colorectal tumors (Kumar M et al. 2010).

And they found good evidence that probiotics yield colonic metabolic changes that weaken carcinogens, create compounds that protect against cellular mutation, and enhance the body’s natural immune response.

The Indian review team concluded that lactic acid bacteria — like those in yogurt, kefir, fermented vegetables, and many probiotic supplements — “offer potential as [cancer] chemo-protective agents ...”.

Baylor study finds promise in a common probiotic bug
Important findings were recently reported by a team of researchers from the Baylor College of Medicine in Texas (Gao C et al. 2017).

The Baylor team studied a probiotic — Lactobacillus reuteri — which is commonly found in fermented foods and probiotic supplements, and has been shown to reduce intestinal inflammation, which is a known risk factor for colorectal cancer. .

Lactobacillus reuteri (L. reuteri) occurs naturally in human breast milk and in the human microbiota. 

But L. reuteri levels vary from person to person, and not everyone harbors significant amounts.

Probiotic foods or dietary supplements containing L. reuteri — look at their labels — can create and sustain high gut levels of this probiotic, but they may decline unless consumption is maintained.

Previous research has shown that animals with low levels of an enzyme known as HDC — histidine decarboxylase — suffer an increased risk of chronic bowel inflammation, and a higher consequent risk of developing colon cancer.

HDC converts the amino acid L-histidine into histamine, which your body uses to regulate its immune response.

And L. reuteri produces HDC in humans and animals alike — which may be why it can reduce intestinal inflammation, and may help guard against colon cancer. 

The Baylor team analyzed the effects of supplemental L. reuteri bacteria on mice that were lacking HDC, to determine if it could reduce inflammation and the creation of tumors in animals subjected to carcinogenic toxins.

The Baylor researchers fed supplemental L. reuteri to mice deficient in HDC. As expected, the probiotic raised HDC and histamine levels alike.

More importantly, carcinogen-exposed mice fed L. reuteri showed fewer and smaller tumors than the control group.

In addition, the probiotic reduced inflammation and stopped the creation of new cancer cells.

The Texas team also analyzed data from more than 2,000 colon cancer patients, and found that survival rates were higher in patients with higher HDC and histamine levels.

These findings strongly suggest that histamine-generating probiotics like L. reuteri may help prevent colorectal cancer and/or improve outcomes for patients with the disease.

As lead author Dr. James Versalovic said, “By simply introducing microbes that provide missing life substances, we can reduce the risk of cancer and supplement diet-based cancer prevention strategies.”


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