2. From bacteria to obesity, diabetes and ulcerative colitis

A good part of the studies on the microbiome are done on feces, as the gut is home to more than 90% of all the microorganisms in our bodies. In 2011, one of these studies divided the population into three groups according to the composition of the bacteria in their feces (enterotypes). Belonging to one group or another seems to be linked to a tendency towards obesity or to develop diabetes. One possible explanation for these results, however, could be that the accumulation of fat changes the bacteria and not that they play a role in causing obesity.

Nevertheless, during the B·Debate, Karine Clement, director of the Institute of Cardiometabolism and Nutrition in Paris, cited a famous study (see below) that suggests that certain microorganisms do in fact promote obesity.

Clement’s own team has proven that the greater the microbial diversity, the more effective a diet will be in promoting weight loss. And that this may be due, in part, to a type of bacteria mentioned many times by the experts at this B·Debate: Akkermansia muciniphila (AKK). The hypothesis is that if there is inflammation (irritation) “certain defense cells may enter the intestinal cells, altering their reaction to insulin and affecting nutrient absorption,” explained Clement. AKK may protect intestinal cells by taking care of the mucosal barrier that protects them and reducing inflammation. The difficulties in cultivating this type of bacteria explain why it hasn’t yet been studied as a treatment.

Changes in the intestinal microbiome may also explain the origin of ulcerative colitis, an illness, Francisco Guarner recognizes, “we don’t know the origin of.” However we do know that “the number of cases has increased in recent years, that genetics doesn’t seem to be very important and that there isn’t a therapy to treat it yet.” At the B·Debate, Guarner showed how patients with this type of colitis have lower microbial diversity than healthy people –especially those who tend to have more episodes- while four strains of bacteria are missing nearly entirely in these patients, among them, AKK.

Microorganisms that make you gain weight: the experiment in mice

A famous study by the team led by Karine Clement, director of the Institute of Cardiometabolism and Nutrition in Paris, suggests that certain microorganisms may cause obesity. In the study, they transplanted feces from a set of twins, one obese and one thin, into mice. The mice with the feces from the obese twin gained a lot more weight than the ones with the feces from the thin twin. And if they were put together for some time, the thinner mouse was able to pass those bacteria to the obese one and protect it (as long as their diet was somewhat under control).