Gut bacteria and especially their composition affect health and the risk of developing many diseases. Now a new study shows that the composition of gut bacteria very much depends on the physiological and environmental conditions in the gut. A researcher says that this increases awareness of the links between environmental factors in the human body, bacteria and health.
Recent health research has focused intensely on how the composition of gut bacteria affects health. Research has established that unhealthy composition of gut bacteria is often associated with many health conditions, including diabetes, obesity, Alzheimer’s disease and cardiovascular disease.
The big question that researchers are asking is what determines the composition of gut bacteria and whether this can be changed to promote health.
The researchers behind a new study addressed this question and found that the environment of gut bacteria is strongly linked to the composition.
The research has been published in Nature Microbiology.
“The conditions bacteria encounter differ from the time they enter the stomach to the time they exit. With this study, we aimed to determine what happens in the gut, how these conditions differ throughout the gut, how these conditions differ between people and how this all relates to the composition and activity of bacteria,” explains a researcher behind the study, Henrik Roager, Associate Professor, Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark.
Fifty people on a SmartPill
The researchers recruited 50 healthy adults not taking medication to eat a standardised breakfast and then swallow a wireless motility capsule (SmartPill) that measures temperature, pressure and pH in the gut.
The participants were also fitted with a portable receiver that picked up the signals from the SmartPill as it passed through the esophagus, stomach, small intestine, large intestine and rectum.
Using the data, the researchers determined the conditions in the different parts of the gut and how long the SmartPill and the breakfast took to travel through the parts of the gut.
All this provided insight into various aspects of each person’s gut physiology and environment and the differences between the participants.
Participants varied considerably
The participants varied greatly. For example, the pH in the small intestine varied between individuals from 6.5 to 8.5, a factor of 100 since pH is logarithmic.
Likewise, the transit time for the participants varied from 2 to 10 hours in the small intestine and 2 to 63 hours in the large intestine.
“The transit time and pH probably affect how people react to the food eaten. The breakdown of the food components by digestive enzymes depends on pH, and so does absorption of the nutrients, and also gut bacteria are affected by differences in pH. In other words, differences in transit time and pH can influence how people react to the food eaten, and these differences may explain why some people break down and absorb it rapidly, whereas for others the food may pass less digested through the gut,” says Henrik Roager.
Transit time influences the composition of gut bacteria
pH, transit time and the composition of bacteria are linked. A long versus short transit time was associated with differences in composition. Since the composition is linked to health, differences in transit time are likely to affect health.
The composition of bacteria could theoretically affect the transit time, but Henrik Roager is more inclined to think that causal direction is that the transit time affects the composition of bacteria.
“One causal direction does not necessarily exclude the other, and other factors can affect transit time. For example, men typically defecate more frequently than women, and exercise increases peristalsis and thus reduces transit time,” explains Henrik Roager.
Shorter transit time lowers the gut pH
Slower transit time and thus slower digestion is associated with higher diversity of the gut bacteria that are associated with being healthier.
However, Henrik Roager thinks that there are limits to this. For example, he does not think that constipation necessarily results in a healthier composition of gut bacteria.
The research also shows that longer transit time and higher pH result in more protein fermentation when dietary fibre is depleted.
According to Henrik Roager, this is interesting because the bacteria only begin to break down proteins when they run out of dietary fibre. With the longer transit time, the bacteria have more time to digest all the dietary fibre and thus begin fermenting protein.
“However, fermentation of protein results in substances that are potentially harmful and associated with an increased risk of developing cardiovascular disease. A longer transit time also results in increased methane production. We can measure this in exhaled air, since methane is absorbed through the intestines into the blood and then excreted through the lungs. The amount of methane is also related to the transit time,” he notes.
Taking good care of the gut ecosystem
Henrik Roager says that the new study has improved understanding of why people react differently to the food and beverages consumed.
A certain diet can cause some people to gain weight and become unhealthy but does not cause this among other people because their intestinal physiology differs and therefore the composition of their gut bacteria and how they process and absorb food.
“We are constantly learning about the complex interaction between gut bacteria, the gut and health and how changing diet, changing lifestyle or using antibiotics can create balance or imbalance in the gut. Having a stable ecosystem and supporting it with a varied diet are crucial. If we do not take care of this ecosystem and it collapses, this can strongly affect our health in both the short and long term,” concludes Henrik Roager.
“Gut physiology and environment explain variations in human gut microbiome composition and metabolism” has been published in Nature Microbiology. The Carlsberg Foundation and the Novo Nordisk Foundation supported the research.
