Cancer, Diet and Gut Bacteria

On Monday, I read a little article on Medical Express about a multi-center research study done in Spain, just published in the journal, Nutrients, which took an in-depth look at the association between diet and the development of both breast and colorectal cancer.[i]   Thousands of cases of cancer, as well as healthy controls, were analyzed and the scientists found that those who ate an inflammatory diet (which included a high consumption of red and processed meat, saturated and trans fats, and refined carbohydrates) had twice the risk of developing colorectal cancer than those who ate an anti-inflammatory diet (consisting of predominantly plant-based foods, like vegetables, fruit, legumes and nuts).  Interestingly, they did not find an association with breast cancer.  (They intend to look into this further in the future.)

Ordinarily, while interesting, this wouldn’t merit a blog post from me as it is hardly surprising, but within minutes of finishing reading it, I read a second article, this one out of the Baylor College of Medicine, on the exact same topic:  the relationship of diet to colorectal cancer.[ii]  As it is the 4^th most common cancer in the world, well…now this relationship did seem worth reporting to you, especially since there is such synergy between the two studies.

The Baylor researchers, noting this relationship, are actually trying to figure out the mechanism of action.  How does diet influence the risk of this cancer?  These scientists had already shown, in a previous study, that a healthy diet was associated with a decrease in the risk of pancreatic cancer.  They now have taken that research a step further.

It turns out that there is an association between “…diet quality and microbiome composition in the gut mucosa.”  These scientists found that “…a high-quality diet is linked to more potentially beneficial bacteria; while a low-quality diet is associated with an increase in potentially harmful bacteria.”  While this too is hardly shocking, what IS really interesting about this Baylor study is that rather than looking at individual diets, they looked at dietary patterns (I’ll come back to this in a moment), and secondly, they looked directly at the gut bacteria in the mucus lining of the intestines (from consenting adults having colonscopies), as opposed to analyzing fecal samples.  Since the gut bacteria influence, “…nutrient uptake, synthesis of vitamins, energy harvest [i.e. how calories are derived from food and used or stored], chronic inflammation, carcinogen metabolism and the body’s immune and metabolic response…,” well, obviously the microbiome has tremendous influence on the development of disease.

In terms of dietary patterns, they compared the foods the participants ate to the Healthy Eating Index (HEI)-2005, and looked at how particular groups of foods affected the gut bacteria.  Lower scores on the index are given for whole fruits (HEI 1 and HEI 2), while added sugar, trans fats and alcohol are HEI 12s.  They found not only that there were distinct differences for let’s say, HEI 7 (lower Faecalibacterium and Fusobacterium but higher Bacteroides) as compared to, for example, HEI12 (lower Subdoligranulum but higher Escherichia and Fusobacterium), but also that “A lower score for total HEI–2005 was significantly associated with reduced relative abundance of potentially beneficial bacteria but increased potentially harmful bacteria in the colonic mucosa of endoscopically normal individuals.”[iii]

The bacteria in the mucosa are associated directly with both immunity and host-microbiome interaction, apparently more so than fecal bacteria.  These researchers found “…a good-quality diet as the one recommended by the Dietary Guidelines for Americans to be high in fruits, vegetables and whole grains, and low in added sugar, alcoholic beverages and solid fats is associated with higher abundance of beneficial bacteria such as those with anti-inflammatory properties. A poor-quality diet, on the other hand, is associated with more potentially pathogenic bacteria, such as Fusobacteria, which has been linked to colorectal cancer.”

Essentially, they conclude that by affecting the structure of the mucosal microbiome, diet affects immunity, thus inflammatory status…thus the risk of cancer and other chronic diseases.

This of course, completely coincides with the findings of the Spanish scientists, I mentioned early.  And you all know how much I love coincidences!

Going forward, this team wants to look in greater depth at bacterial metabolites (like short chain fatty acids, for example) to see how these affect the growth of tumors, as well as looking how we can modify the gut bacteria using pre- and pro-biotics,  even in those with a poor diet.

In the meantime though – not exactly a news flash: eating a healthy diet seems like a pretty good idea.

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[i] https://medicalxpress.com/news/2019-07-inflammatory-diet-colorectal-cancer.html

[ii] https://www.bcm.edu/news/research/diet-influences-microbiome-colonic-mucosa

[iii] Liu, Y, et. al. Dietary quality and the colonic mucosa – associated gut microbiome in humans. The American Journal of Clinical Nutrition. 2019.  https://doi.org/10.1093/ajcn/nqz139