March 4, 2018

It's All in the Gut

Marcos Paseggi, Adventist Review

What follows is part of a series of reports on presentations given at the Seventh International Congress on Vegetarian Nutrition in Loma Linda, California, United States, from February 26-28, 2018. Individual stories provide a summary of various topics covered and the presentations made throughout the event. ~ Adventist Review Editors

A common research search engine shows that studies of the gut microbial flora have skyrocketed in the last few years. Microbial genome, or the microbiome, seems to be a promising new area of research, said Michael J. Orlich, who teaches at School of Public Health at Loma Linda University.

It is not, however, a “new” science, he reminded. Its origins can be traced back to gut flora researchers from the 17th century onwards, including 19th-century studies on the benefits of yogurt consumption for gut health. It also includes former Seventh-day Adventist physician John Harvey Kellogg around the turn of the 20th century. Kellogg wrote extensively on the importance of intestinal health for overall health.

The topic is back, explained Orlich, because now there are new and better tools to do research. “A question we asked is,” he said, “whether it is possible that some of the health benefits observed in a vegetarian diet may be due to a different microbiome.”

Some recent studies show that diet indeed affects microbiome, but not in the way some researchers would expect. “Review of three studies show that the amount of dietary fiber and the amount of plant and fruits consumed may explain differences better than just being vegan, ovo-lacto-vegetarian, or non-vegetarian,” acknowledged Orlich.

Why Berries Are Good for Your Gut

Recent data suggest that consumption of polyphenol-rich foods such as berries are associated with microbial diversity in the gut, which is highly beneficial, said Aedin Cassidy, professor of Nutrition at the University of East Anglia, in England. Special research interest has been given to the interplay with one class of polyphenols/flavonoids, the anthocyanin sub-class.

Cassidy explained that changes after anthocyanin intake resulted in improvements in inflammation and insulin sensitivity. “This provides the first convincing data…that flavonoids enhance the health effects of the gut microbiome.”

Specific studies on berries consumption have been revealing, she said. “Berry intake slows cognitive decline, and has shown to reduce the risk of hypertension, diabetes, Parkinson’s, and heart disease,” said Cassidy.

The important thing, she said, is knowing that the food we eat can alter our gut microbiome. “Human gut microbiome rapidly responds to a change in diet,” said Cassidy as she shared the results of a study where subjects showed altered microbial metabolic activity in their gut just five days after altering their diet.

It is a science in its infancy, and new studies are needed to explain associations between anthocyanins and cardiometabolic health. Meanwhile, we’d do very well in eating anthocyanin-rich foods such as berries, Cassidy said.

Why Nuts Are Good for Your Gut

Consumption of nuts has been associated with reduced risk of cardiovascular disease and certain cancers, reminded David J. Baer, Research Leader at the US Department of Agriculture in Maryland. Incorporating tree nuts, for instance, in your diet, lowers the LDL cholesterol, which is an established risk factor for coronary disease. He also referred to studies that show that a walnut-enriched diet reduces the growth of prostate cancer.

Contemporary research is beginning to focus on the mechanisms by which diet alters risk for cancer, something that has produced an increased interest in understanding better what happens in the gut. But why?

According to Baer, nuts are a unique food group “in that they deliver more dietary fat to the large intestine (a site of significant anaerobic fermentation in humans) than most other foods.” Emerging data suggest nuts may help to reduce cardiovascular disease and cancer through effects on the microbiome.

Studies with nuts have shown how they help the gut, for instance, to produce butyrate, which has a barrier function and helps in immune regulation and intestinal motility. Walnuts, specifically, also reduce the concentration of secondary bile acids, which lead to higher risk of colon cancer.

“Nuts can alter the composition of the gut microorganisms,” said Baer. “And nut-induced microbially-produced compounds are associated with reduced risk for cardiovascular disease and cancer.”

A Word of Caution

As new studies are conducted, researchers should be cautious about jumping to conclusions, warned Orlich at the end of his presentation. “Some of the current diet and microbiome emphasis play on hype and may be oversold,” he said. “Still, there are high hopes for advances in this area.”