Duke researchers are exploring how the human gut microbiome affects digestion and fecal particle size.
The study, led by Jeff Letourneau, PhD, while in the lab of Lawrence David, PhD, associate professor of molecular genetics and microbiology, examined how chewing efficiency and food processing impact the microbiome and fecal particle size in humans.
Previous studies have shown that fecal particle sizes in animals correlates to how they chew. For example, a snake, which eats its prey whole, has large fecal particle sizes, while a mouse that chews small bites out of food has small fecal particle sizes.
This made Letourneau wonder how chewing food might affect fecal particle sizes in humans. “Essentially, what you’re doing to the input relates to the particle size of the output,” Letourneau said. “There’s a lot of evidence to support that, so my question, assuming this would happen in humans, was what’s the effect on the microbiome?”
So, he started a two-week-long human research trial. In the first week, participants ate normally. In the second week, they were asked to chew every bite of their food thoroughly – until it was the consistency of applesauce. Participants provided stool samples every few days that researchers then analyzed using laser diffraction to determine fecal particle sizes.
The results were surprising: unlike other animals, fecal particle sizes did not change in response to how efficiently human participants chewed their food. “I suspect the difference between animals and humans has to do with the fact that we eat a much more processed diet,” Letourneau said.
While they didn’t find any differences in fecal particle sizes based on chewing, they did find evidence that the gut microbiome plays a role in determining particle sizes through digestion.
“When you’re dealing with large particles, there’s only so much external surface area,” Letourneau said, “but as we break that into smaller and smaller particles, there’s more surface area available.”
But there are also differences in the compounds made by the bacteria in the microbiome. In the early stages of digestion and fermentation, microbes tend to produce compounds that have more health benefits, like short chain fatty acids, which comes from the fermentation of fiber.
The longer digestion takes, though, the more researchers start to see protein fermentation, and less beneficial or even detrimental compounds, like branch chain fatty acids.
Longer digestion leads to smaller fecal particle sizes, and an increased likelihood of issues like constipation.
Ultimately, the study presents the gut microbiome as an intricate, physically structured ecosystem. “If you think of any forest, you have things living inside of the nooks of trees and other animals going at them, and then the trees are falling and fungi are degrading them,” Letourneau said. “It’s a lot of those same dynamics that we may not think of in this ecosystem within us that are also playing out there as well.”