There are those who remain skinny as a rail regardless of what they eat, and those who swear they can gain weight just by looking at food. Question of metabolism, but not only. The intestinal microbiome in fact seems to play a leading role in mediating the quantity of calories we extract from food, making some people – in particular, those who host a greater quantity of methane-producing bacteria in their intestinal flora – particularly capable of obtaining energy from dietary fibre, and therefore also more exposed to the risk of gaining weight. This is suggested by a study published in the journal The ISME Journal by a team of researchers from Arizona State University.
The microorganisms that help us digest
The intestinal microbiome is an ecosystem made up of very different microorganisms, which live in our intestines and play a symbiotic role with our body, helping us to keep pathogenic bacteria and other unwanted visitors away, training our immune system, but above all, helping us to digest food and obtain the nutrients we need to survive. Some bacteria have the task, for example, of fermenting the dietary fibers that reach the intestine – an activity that the enzymes present in our stomach cannot do – transforming them into short-chain fatty acids that can be used as a source of energy by the body’s cells.
During this process, hydrogen is produced, which accumulates in the intestine until it reaches a threshold beyond which the fermentation activity of the fibers is paused. Since the microbiome is a microbial ecosystem, however, there are many other bacteria that come into play to modulate this balance. In particular, a class of microorganisms known as methanogens, which use hydrogen as an energy source – reducing its intestinal concentration – and in turn producing methane. It is known that in this way they can improve fermentation, but until now the effect they have on the metabolism of our species has never been studied in depth. A gap that researchers from Arizona State University decided to fill in their new study.
The experiment
The research was carried out in a special room, in which a group of volunteers took turns living for a week in extremely controlled conditions, receiving standardized portions of food, and under constant monitoring to evaluate their energy consumption, their body’s metabolic activity and their methane emissions. By analyzing the participants’ blood and feces, the researchers were then able to precisely calculate how much energy they absorbed from food. And they then cross-referenced the information on calorie absorption with that on methane emissions, to verify whether the greater presence of methanogenic bacteria in the microbiota actually influenced in some way the efficiency of intestinal fermentation, and therefore energy production.
During the experiment, the participants were fed two different diets, equivalent in terms of calories: one rich in processed foods, and a healthier one with high amounts of fiber and whole foods. In the first case, methane production was not linked to differences in calorie absorption (in any case a superior result). For the diet rich in fibre, however, the differences were evident: the greater the production of methane, the greater the quantity of calories that were absorbed by the body. The methanogenic bacteria would therefore be able to improve the efficiency of fiber fermentation in the intestine, providing more calories – for the same amount of food ingested – to people who have high levels of them in their microbiota.
“This difference has important implications for dietary interventions, because it shows that people can respond very differently to the same diet, in part due to the composition of their gut microbiome,” explains Blake Dirks, a researcher at Arizona State University who participated in the study. “In our study the participants were all relatively healthy. And it is a detail that I believe will be important to investigate further in the future, studying how obese people, diabetes and other health problems respond to these fiber-rich diets.”