April 21, 2011

What’s Your Gut Type?

The human digestive system, a hotbed of living bacteria, comes in three variations just as distinct as variations in blood type, according to a study released on Wednesday.

These "enterotypes" are found in people around the world and exist independent of race, origin, diet, body mass index (BMI), age and state of health, the study says.

Researchers from the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, collaborators in the international MetaHIT consortium, and scientists from the VIB and Vrije Universiteit Brussel, have found that humans have 3 distinct gut types.

"The three gut types can explain why the uptake of medicines and nutrients varies from person to person," says bioinformatician Jeroen Raes of the VIB and Vrije Universiteit Brussel. "This knowledge could form the basis of personalized therapies. Treatments and doses could be determined on the basis of the gut type of the patient."

The findings have huge implications for detecting and predicting the risk of diseases of the digestive system, including intestinal cancers, Crohn's disease and diabetes, among others, researchers say.

Everyone has bacteria in their gut that help digest food, break down toxins, produce vitamins and amino acids, and form a wall against harmful intruders. But the chemical makeup of that bacterial community varies from individual to individual.

"We found that the combination of microbes in the human intestine isn't random," said Peer Bork at EMBL, leader of the study. "Our gut flora can settle into three different types of community "“ three different ecosystems, if you like."

Bork and colleagues initially used stool samples to analyze the gut bacteria of 39 individuals from three different continents (Europe, Asia and America). They later extended the study to an extra 85 people from Denmark and 154 from America.

The researchers found that all the cases could be divided into three groups based on which species of bacteria predominantly occurred in their gut. These three types are called: bacteroides, prevotella and ruminococcus.

The team of scientists are not yet sure why people have these different gut types, but speculate that they could be related to differences in how their immune systems distinguish between harmless and harmful bacteria, or to different ways of releasing hydrogen waste from cells.

However, scientists did find that the guts of older people appear to have more microbial genes involved in breaking down carbohydrates than do youngsters, possibly because as we age our digestive tract becomes less efficient at processing those nutrients, so in order to survive in the human gut, bacteria have to take control.

"The fact that there are bacterial genes associated with traits like age and weight indicates that there may also be markers for traits like obesity or diseases like colorectal cancer," Bork said, "which could have implications for diagnosis and prognosis."

If this proves true, when diagnosing the likelihood of a patient contracting a specific disease, doctors could look for clues in the bacteria that live in the body. And after diagnosis, treatment could be adapted to the patient's gut type to ensure the best possible results.

The team of researchers also showed that certain strains of bacteria -- varying in concentration in the three gut types -- boost the likelihood of obesity, a finding that could shed light on why some people have a harder time losing weight than others.

"The more efficiently the bacteria extract energy from food, the greater the chance that the person has a high BMI," said study co-author Stanislav Dusko Ehrlich, a professor at France's National Agronomy Research Institute.

"Looking at the genes of the microbiota tells us with much greater precision than looking at the genes of the individual if someone is obese or not," Ehrlich told AFP.

More than a hundred trillion bacteria -- up to 1,000 different species -- live inside the human gut, where they are a crucial part of the digestive process and protect us from pathogens. In exchange for this natural service to our body, our digestive tract provides bacteria with food and shelter.

Bacteria is a crucial part of human health, but when disrupted they can lead to poor digestion and in some cases, even death.

"Certain species of bacteria can become overly abundant, while others can disappear. It can happen at any point in one's life," said Ehrlich.

Researchers can aim to design treatments that seek to stimulate "good" bacteria, or restrain the growth of harmful bacteria, in order to establish a balance, he added.

"We can even imagine one day 'transplanting' the microbiota of a healthy individual into that of a patient suffering from a serious disease," he said.

"Ecosystems have a tendency to evolve toward a stable equilibrium, with certain species becoming dominant while others occupy niches," said Raes. "This also appears to apply to our intestines," he added, comparing the microbiota in the human gut to forests, tundra or tropical jungles.

It is still not known if a person can switch from one group to another over the course of their life, researchers said.

The study also found that vitamin production varied greatly between the three gut types. People in the bacteroides group were better able to generate vitamin C, B2 and B5, while those in the prevotella group showed higher levels of B1 and folic acid.

The researchers pointed out that the findings were based on samples from several hundred people, and that more research is needed to determine if more types of bacterial ecosystems thrive in the human gut.

The study was published Wednesday in the journal Nature.


Image 2: This is an artistic impression of the three human gut types. Credit: EMBL/P.Riedinger


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