A 2006 study published in Nature showed that obese people had a different type of intestinal flora. It was not known, however, whether obesity was a cause or consequence of this difference.

In 2009, American researcher Jeffrey Gordon of Washington University, suggested that fat was a consequence of the intestinal type of environment. He said that people should know what type of bacteria is in your gut to see if they were more vulnerable to obesity. Another study published in Nature shows that there are three different types of intestinal flora, just as every human has a blood type. Each one represents different types of predominant bacteria in the intestine, which were unrelated to ethnicity, national origin or manner of feeding.

Since each bacterium has a different efficiency at the time of extracting energy from food, the hypothesis is that the metabolism (slow or fast) to be correlated with the type of intestinal flora. Scientists from several institutions, in collaboration with the Federal University of Minas Gerais, have failed so far to point out which of the three intestinal flora is retard or increase metabolism.

They plan to repeat the work. However, even if they get new results, certainly not the intestinal type is the only explanation for obesity. Other factors are the most prevalent type of diet, physical activity level and other genetic issues. Anyway, one should not underestimate the role of bacteria in the human body. And they are many: while the human body has about 10 trillion cells, each person carries more than 300 trillion bacteria of all kinds.

Pholia Negra