New research has examined the effect of dietary quality on the composition of the colon's microbiota. The study suggests that following a high quality diet may increase the number of beneficial bacteria, whereas following a low quality diet may raise that of harmful bacteria.

An increasing number of studies are pointing out the links between diet and health.

For instance, some researchers have warned that ultra processed foods may raise the risk of cancer.

Meanwhile, some foods — such as whole grains or broccoli — may keep the condition at bay.

However, most of these studies are observational, meaning that they only show an association between food intake and cancer occurrence. The mechanisms behind these correlations remain the subject of more investigation.

Recently, researchers aimed to fill some of this gap in knowledge by addressing the microbiotic composition that is associated with different quality diets.

Dr. Li Jiao — an associate professor of medicine gastroenterology and a member of the Dan L. Duncan Comprehensive Cancer Center at the Baylor College of Medicine in Houston, TX — led the scientists.

To analyze bacteria in the human colon, Dr. Jiao and team used a gene sequencing technique called "16s RNA sequencing" on 97 biopsies of the colonic mucosa obtained from 34 healthy people.

The study participants reported the quality of their diets using food frequency questionnaires, and the researchers examined the association between different diets and the health of the colon samples.

Dr. Jiao and colleagues published their findings in the American Journal of Clinical Nutrition.

Why study the colon's microbiome?

The participants consented to having a colonoscopy in 2013–2017, and they did not present with any colonic polyps at that time.

The adults were ages 50–75 at the time, and they all filled in a food frequency questionnaire before the procedure. Dr. Jiao explains why the researchers used colonic samples, saying, "One new contribution [of] this work is that we looked at the microbiome associated with colonic mucosa."

"Most other studies of the human gut microbiome have used fecal samples," adds Dr. Jiao.

"We looked at [the] colon mucosa associated microbiome because we know that this microbiome is different from that in the fecal samples, and it is said to be more related to human immunity and the host–microbiome interaction than the microbiome in fecal samples."

The researchers assessed the quality of the participants' diets using the Healthy Eating Index (HEI). This is "a measure of diet quality, independent of quantity, that can be used to assess compliance with the [United States] Dietary Guidelines for Americans."

"In this study, rather than looking at individual diets, we focused on dietary patterns as defined by the [HEI]-2005 and how they relate to the microbiome," explains Dr. Jiao.

"In a previous study, we found that HEI-2005 is associated with reduced risk of pancreatic cancer," she adds.

Aiding healthy living through the microbiome

Using the HEI, the researchers established that a diet rich in fruits, vegetables, and whole grains, but low in added sugar, alcohol, and solid fats is a high quality diet.

Following this diet correlated with having a higher level of beneficial bacteria — that is, bacteria with anti-inflammatory properties.

By contrast, following a poor quality diet correlated with an increase in potentially harmful bacteria, such as Fusobacterium. This is a genus of bacteria that previous studies have linked to colorectal cancer.

Dr. Jiao also comments on the significance of the findings, drawing empowering conclusions for people who want to stay healthy by watching their diet.

"Other factors, such as aging, genetics, or certain medications, also influence the risk of disease, but we cannot modify them," Dr. Jiao says.

"Diet, on the other hand, can be modified and thus provides a strategy to develop a microbiome that promotes healthy living. We suggest that modifying the microbiome through diet may be a part of a plan to reduce the risk of chronic diseases." Dr. Li Jiao