Innovative capsules capture the gut environment’s impact on microbiome variations and metabolism

Researchers at the University of Copenhagen, Denmark, have used a wireless motility capsule to reveal how changes in the gut environment impact bacteria composition and activity. The team believes the findings may help explain differences in people’s gut microbial composition and metabolism.

In the study, 50 healthy individuals swallowed a capsule with breakfast for nine consecutive days. These motility capsules, SmartPills, measure pH levels, temperature and pressure along the gastrointestinal tract to determine transit times. 

The team found substantial daily fluctuations, with variations between people’s microbiome and metabolism and variations within individual participants linked to transit times and pH levels in their digestive systems. 

Speaking to Nutrition Insight, lead researcher Henrik Munch Roager, an associate professor in the university’s Department of Nutrition, Exercise and Sports, hopes the study will “make people realize that we are unique — also in our gut.” 

He says this may be key to understanding why people respond differently to the same food. 

“Furthermore, I hope our results will stimulate more research that seeks to understand gut physiology shapes our community of microbes in the gut.” 

Variations in pH across digestive system

Instead of relying on traditional stool samples, the team measures the environment throughout the intestine using SmartPills. The results are published in Nature Microbiology. 

“This way, we could demonstrate that, for instance, pH in the small intestine varies substantially between individuals. Our results also emphasize that intestinal transit time and pH are key factors that explain variations in gut microbiome composition and activity,” says Roager. 

“We know that pH is a crucial factor in bacterial growth and activity, so it made perfect sense that we could see that gut environment and pH are linked to differences in the composition and activity of the gut bacteria. This means that the environmental conditions we each have in our gut can help explain why we have different bacteria in the gut.”

The capsule registered a very low pH value in the stomach, as acids break down foods. In the small intestine, a higher pH level is recorded as gut cells release alkaline bicarbonate to neutralize stomach acid. 

Participants consumed the capsules with rye bread with butter and jam, a boiled egg, yogurt, nuts, blueberries and a glass of water.In the large intestine, food is fermented by gut bacteria, which produce fatty acids that reduce the pH values of the colon’s first part. However, the capsule recorded incremental rises in pH levels along the large intestine as fatty acids are absorbed and the gut bacteria activities change. 

Roager says that the team estimated how long the food was in different parts of the gut based on these changes in pH recorded by the SmartPills. 

Transit time for the capsules through the small intestine varied among participants, taking between two to ten hours. Roager says that as most of the nutrients are absorbed in this part of the digestive system, travel time differences “probably have an impact on how much of the nutrients we absorb and how much passes on to the large intestine.” 

Implications for personalized nutrition

The new knowledge could be helpful for future nutritional guidelines, as it shows that people digest and absorb food differently, which could be driven by their gut environment.  

For example, the researchers identified metabolites with longer transit times that have been reported as elevated in people with constipation. Some acids were associated with a longer intestinal transit time, higher pH and bacteria consistently associated with constipation. 

The authors note that more research is needed to explore “the relationship between gut physiology and microbiome under controlled diets, possibly involving dietitians or providing whole diets.”

Roager says that using samples from the whole gastrointestinal system instead of stool samples would advance gut microbiome research.“The study gives another rationale for why personalized nutrition is relevant to discuss, as it shows that we are all unique in our gut,” Roager adds. 

“At this point, we cannot give advice based on this knowledge, but in the future, we may be able to understand better gastrointestinal symptoms and digestion in light of differences in gut physiology.”

Intestinal research advances

Although traditional research relies on stool samples, scientists are advancing gut microbiome research through innovative pills and capsules like the SmartPills. For example, US Tufts University School of Engineering researchers developed a pill to make a full inventory of microorganisms in the gastrointestinal tract.

Lallemand Health Solutions recently partnered with Nimble Science to assess the efficacy of its probiotic strain by collecting and preserving samples from the small intestine through Nimble’s SIMBA Capsule. 

Relying on stool samples to build knowledge of the gut microbiome is a crucial limitation, says Roager. Scientists compare these samples with what a person has eaten. 

“This sample reflects mostly the distal part of the colon. If we could get samples throughout the whole gastrointestinal system, we could better link regional differences in microbes to the differences in gut physiology and environment.” 

“We are still excitedly waiting for devices that can sample material throughout the intestine to become widely available,” he concludes.