High-fiber diet makes big changes to human gut microbiome, study finds

Short-term intervention in daily fiber intake can dramatically alter the gut microbiome and nutrient intake, according to a study by researchers at Irvine at the University of California. The research was recently published by the American Society for Microbiology.

Dietary fiber is made up of resistant carbohydrates found in fruits, vegetables and whole grains. Fiber persists in our digestive system, and although it is not digestible by humans, our gut bacteria can metabolize fiber into short-chain fatty acids and other byproducts essential for human health.

Right now, the average person in North America is consuming less than 50 percent of recommended dietary fiber levels due to decreased consumption of plant-based foods as processed foods have become widespread. A low-fiber diet is of concern to health officials, as low intake of dietary fiber may be associated with diseases like type II diabetes and colon cancer. Additionally, new studies have started to demonstrate how gut microbial changes can indirectly impact human health. Therefore, a better understanding of the role of dietary fiber on the constitution of the gut microbiota could provide information on the management of diseases associated with the gut microbiome.

“The lack of fiber in the industrialized world is starving our gut microbes, with significant health consequences that may be associated with an increase in colorectal cancer, autoimmune diseases and even decreased vaccine effectiveness. and response to cancer immunotherapy, ”said Katrine Whiteson, associate professor of molecular biology and biochemistry who co-leads the UCI Microbiome Initiative.

To determine whether increasing dietary fiber for a short time could alter gut microbiome diversity and metabolite production, a research team led by UCI Microbiome Initiative co-directors Whiteson and Professor Jennifer Martiny ecology and evolutionary biology, with Julia Massimelli Sewall, assistant professor teacher, set up a two-week dietetic intervention during an undergraduate biology course at UCI.

Students who participated in the study were given 10 unprocessed high-fiber meals each week for two weeks. During this time, they took samples to monitor their gut microbial composition before and after the procedure. The students also recorded their dietary macronutrient information to achieve a goal of 50 grams / day during a two-week intervention period.

Sewall, the course instructor, noted how much she and the students enjoy learning which foods are fortified with fiber. “We were amazed at how rich the fiber berries and avocados are and exchanged ideas on how to prepare beans and lentils,” she said. “I think this experience will have a lifelong impact on the way we all look at nutrition labels.”

She also noted that the research experience motivated the students of the course. “The students came to class very excited to discuss what they had eaten and couldn’t wait to analyze the microbiome sequencing information to draw data-driven conclusions. The study had an interesting and educational impact, ”she added. “Our educational research showed that the experience increased students’ interest in science and increased awareness of their eating habits.”

Graduate student Andrew Oliver, teaching assistant for the course, mentored the students during the process and advised them to drink plenty of water in addition to teaching them microbiology methods and analyzes. “The students increased their fiber intake by an average of 25 grams per day, but the variability in fiber intake before the procedure was substantial,” he said. “A few students had to go from almost zero to 50 grams per day at the end of the study. We’ve all become a bit obsessed with the amount of fiber in the food we eat.

After the procedure, the researchers compared the overall bacterial composition using DNA sequencing and measured the production of short-chain fatty acids using gas chromatography. In addition to sequencing, the team conducted additional experiments targeting the known fiber degreaser, Bifidobacterium. The researchers found that the two-week intervention significantly altered the makeup of the individual gut microbiome, including an increase in the abundance of Bifidobacterium. However, despite the changes observed in the composition of the gut microbiome, they did not detect any significant change in the abundance of these fatty acids.

“We hope to conduct longer interventions on dietary fiber and study how fiber can support the gut microbiome and promote health. In this time of a pandemic, when we need our immune health and healthy vaccine responses, we encourage everyone to think about plant diversity. of their diet and add beans, berries and avocados where they can, ”Whiteson said.