New study provides fresh insight into why some people gain weight more quickly

It's all about gut microbes.
Mert Erdemir
A fat belly
A fat belly

Ri luck/iStock 

According to a new study by University of Copenhagen researchers, some people have a composition of gut microbes that makes them better at harvesting energy than others. It's a significant step toward understanding why some people put on weight more easily than others, even when they eat the same.

"We may have found a key to understanding why some people gain more weight than others, even when they don't eat more or any differently. But this needs to be investigated further," says Associate Professor Henrik Roager of the University of Copenhagen’s Department of Nutrition, Exercise, and Sports.

Studying the feces of subjects

Researchers examined the remaining energy in the feces of 85 Danes to evaluate the efficiency of their gut microbes at absorbing energy from food. They also mapped each participant's composition of gut microbes.

According to the findings, around 40 percent of the participants belong to a group that, on average, takes more energy from meals than the other 60 percent. The researchers also discovered that people who extracted the most energy from meals weighed 10 percent more on average, equating to roughly 20 pounds (9 kgs) more.

The results indicate that being overweight might be tied to more than how healthy one eats or how much exercise one receives. It might also be related to the composition of a person's gut microbes. Accordingly, some people may be disadvantaged because their gut microbes are very efficient at absorbing energy. Because of this effectiveness, more calories may be available for the human host from the same amount of food.

"The fact that our gut bacteria are great at extracting energy from food is basically a good thing, as the bacteria's metabolism of food provides extra energy in the form of, for example, short-chain fatty acids, which are molecules that our body can use as energy-supplying fuel. But if we consume more than we burn, the extra energy provided by the intestinal bacteria may increase the risk of obesity over time," says Roager.

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Investigating digestive travel times

The researchers also investigated the duration of food's journey in our body for each subject, all of whom had similar dietary patterns. The researchers hypothesized that people with long digestive travel times would get the most nourishment from their diet. However, the study discovered the exact opposite.

"We thought that there would be a long digestive travel time that would allow more energy to be extracted. But here, we see that participants with the B-type gut bacteria that extract the most energy also have the fastest passage through the gastrointestinal system, which has given us something to think about," adds Roager.

"It is very interesting that the group of people who have less energy left in their stool also weigh more on average. However, this study doesn’t provide proof that the two factors are directly related. We hope to explore this more in the future," says Henrik Roager.

The study was published in the journal Microbiome.


Background: It has been hypothesised that the gut microbiota causally affects obesity via its capacity to extract energy from the diet. Yet, evidence elucidating the role of particular human microbial community structures and determinants of microbiota-dependent energy harvest is lacking.

Results: Here, we investigated whether energy extraction from the diet in 85 overweight adults, estimated by dry stool energy density, was associated with intestinal transit time and variations in microbial community diversity and overall structure stratified as enterotypes. We hypothesised that a slower intestinal transit would allow for more energy extraction. However, opposite of what we expected, the stool energy density was positively associated with intestinal transit time. Stratifications into enterotypes showed that individuals with a Bacteroides enterotype (B-type) had significantly lower stool energy density, shorter intestinal transit times, and lower alpha-diversity compared to individuals with a Ruminococcaceae enterotype (R-type). The Prevotella (P-type) individuals appeared in between the B- and R-type. The differences in stool energy density between enterotypes were not explained by differences in habitual diet, intake of dietary fibre or faecal bacterial cell counts. However, the R-type individuals showed higher urinary and faecal levels of microbial-derived proteolytic metabolites compared to the B-type, suggesting increased colonic proteolysis in the R-type individuals. This could imply a less effective colonic energy extraction in the R-type individuals compared to the B-type individuals. Notably, the R-type had significantly lower body weight compared to the B-type.

Conclusions: Our findings suggest that gut microbial energy harvest is diversified among individuals by intestinal transit time and associated gut microbiome ecosystem variations. A better understanding of these associations could support the development of personalised nutrition and improved weight-loss strategies.