Intestinal transit time and microbial community may cause differences in weight gain

Diet and lifestyle 31. jan 2023 2 min Associate Professor Henrik Roager Written by Kristian Sjøgren

Researchers have investigated how intestinal transit time and the composition of the gut bacteria affect how much energy is extracted from food. The results show that some bacteria seem to enable people to extract more energy from the food and that this may increase the risk of overweight. A researcher says that improving understanding of the associations between microbial community structures, the intestinal transit time of food and overweight may be used to create a more individualised diet based on the composition of a person’s gut bacteria.

In recent years, researchers have been learning more about the importance of the composition of gut bacteria for good health. Studies have shown that microbial community structures in the gut appear to be associated with an increased risk of developing overweight or developing underweight.

Now a new study provides more clarity on the entire association between the composition of gut bacteria and the risk of overweight. The researchers show that some compositions of gut bacteria appear to extract more energy from food – and this could potentially end up as stored fat.

The discovery may eventually influence how each person could think about matching their diet with their composition of gut bacteria for preventing weight gain.

“Our study gives rise to several hypotheses about how and why we each extract different quantities of energy from the food we eat. The composition of the gut bacteria may play a role due to some gut bacteria being especially efficient at extracting energy from food. Understanding this association better may enable us to help both people who have underweight and people who have overweight by adjusting each person’s diet so that their gut bacteria either reduce or increase energy extraction,” explains the research leader of the study, Henrik Roager, Associate Professor, Department of Nutrition, Exercise and Sports, University of Copenhagen.

The research has been published in Microbiome.

Examined the stools of 85 people with overweight

The researchers examined stool samples from 85 people in Denmark with overweight for the composition of gut bacteria and residual energy content. Further, the researchers had data on the participants’ weight, habitual diet and intestinal transit time of food.

Henrik Roager explains that people differ greatly in how long food takes to pass through the entire digestive tract – between 12 and 72 hours, during which various digestive processes extract energy from the food.

“We hypothesised that the longer the intestinal transit time, the more energy would be extracted from the food and, furthermore, that the composition of gut bacteria could be linked to energy extraction. Studies in mice have shown that some compositions lead to overweight, but we do not know whether this is because certain bacteria extract more energy from food,” says Henrik Roager.

Composition of bacteria changes the energy extracted from food

The researchers found that long intestinal transit time was surprisingly associated with more residual energy in the stool.

The researchers divided the participants into three groups according to their individual predominant microbial composition.

Bacteroides was dominant in group one, Prevotella in group two and Ruminococcaceae in group three.

The 40% of participants for which Bacteroides was dominant had the shortest intestinal transit time but the least residual energy in the stool. They therefore extracted the most energy from the food and weighed 10% more on average, corresponding to an extra 9 kg compared with the participants in the other two groups.

Conversely, individuals for which Ruminococcaceae was dominant had the longest intestinal transit time for food and weighed the least.

“We think that the bacteria in gut microbial ecosystems characterised by a dominance of Bacteroides generally grow more rapidly than the bacteria in other ecosystems and therefore may also extract more energy from food. We hypothesise that greater energy extraction from food releases more molecules that intestinal cells can use as fuel and that this may influence weight. We cannot demonstrate any causality between the residual energy in the stool and weight in our study, but we noticed that the people with less residual energy in the stool weighed more on average,” explains Henrik Roager.

Designing diet based on gut bacteria

Henrik Roager says that the interactions between gut bacteria and intestinal transit time may have long been overlooked in investigating why some people gain more weight than others, even though they eat roughly the same food.

He thinks that understanding the interaction between the various causal factors needs to be improved to be able to identify what influences the energy extraction from food and how this affects people’s weight.

“We will use our study to establish new hypotheses for how people extract different amounts of energy from the same food and how this affects their weight. If clinical trials validate our hypothesis, a natural next step would be to try to design diets based on the composition of gut bacteria to help both people with overweight and people with underweight,” concludes Henrik Roager.

Stool energy density is positively correlated to intestinal transit time and related to microbial enterotypes” has been published in Microbiome. In 2019, the Novo Nordisk Foundation awarded co-author Tine Rask Licht a Challenge Programme grant for the project PRIMA – towards Personalised Dietary Recommendations Based on the Interaction between Diet, Microbiome and Abiotic Conditions in the Gut.

Henrik Munch Roager is an Associate Professor and Head of the Microbiome & Metabolomics research group at Department of Nutrition, Exercise and Sports...

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