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Gut bacteria can effect weight loss

Gut bacteria keep proving how important they are in helping us maintain good health. Studies have shown that exposure to the right gut bacteria can ward off infection from harmful bacteria like C. difficile. Studies have also linked gut bacteria exposure to development of chronic diseases like asthma and Chron’s disease. Yesterday, the New York Times reported on two studies that together link gut microbe exposure to the weight loss.

In one study, people who are overweight were found to be more likely to have a certain microbe named Methanobrevibacter smithii in their gut. The scientists believe this microbe is better at squeezing nutritional value out of foods and makes it harder for people to lose weight:

The study involved 792 people who had their breath analyzed to help diagnose digestive orders. They agreed to let researchers measure the levels of hydrogen and methane; elevated levels indicate the presence of a microbe called Methanobrevibacter smithii. The people with the highest readings on the breath test were more likely to be heavier and have more body fat, and the researchers suspect that the microbes may be at least partly responsible for their obesity.

This type of organism may have been useful thousands of years ago, when people ate more roughage and needed all the help they could get to squeeze every last calorie out of their food. But modern diets are much richer, said an author of the study, Dr. Ruchi Mathur, director of the diabetes outpatient clinic at Cedars-Sinai Medical Center in Los Angeles.

In the other study, scientist examined the effects of gastric bypass surgeries on the microbiota of mice. The scientist gave one group of mice the surgery and saw their microbiome change significantly while they lost weight. They compared this result to mice who had their intestines surgically separated and stitched back together. This group of mice showed little change in their microbial flora. Implanting the fecal matter from the mice who received the gastric bypass into another set of mice caused the new group to lose weight as well:

the researchers used mice, which they had fattened up with a rich diet. One group had gastric bypass operations, and two other groups had “sham” operations in which the animals’ intestines were severed and sewn back together. The point was to find out whether just being cut open, without having the bypass, would have an effect on weight or gut bacteria. One sham group was kept on the rich food, while the other was put on a weight-loss diet.

In the bypass mice, the microbial populations quickly changed, and the mice lost weight. In the sham group, the microbiota did not change much — even in those on the weight-loss diet.

Next, the researchers transferred intestinal contents from each of the groups into other mice, which lacked their own intestinal bacteria. The animals that received material from the bypass mice rapidly lost weight; stool from mice that had the sham operations had no effect.

Exactly how the altered intestinal bacteria might cause weight loss is not yet known, the researchers said. But somehow the microbes seem to rev up metabolism so that the animals burn off more energy.

Check out the human study here at the Journal of Clinical Endocrinology and Metabolism. The study on mice appars here at Science Translational Medicine.

Everyone knows that bacteria help digest our food, especially in the colon. Fewer people know that gut microbes are also important effectors of the immune system. They help stimulate cells in linings of our guts to produce antibodies to pathogens. The immune system recognizes and fights harmful bacteria, but leaves the helpful species alone. Intestinal bacteria have also been linked to asthma. It turns out that lack of exposure to intestinal bacteria in early childhood can lead to an increase chance of developing asthma. At least in mice.

From Science:

The tricky question is how microorganisms provide this protection. Mice lacking their normal microbial partners and pathogens have now given mucosal immunologist Richard Blumberg of Brigham and Women’s Hospital in Boston and colleagues an insight. Throughout their lives, these so-called germ-free mice dwell in sterile cages and nibble sterile food, so they don’t acquire the intestinal denizens of normal rodents. Compared with their microbe-populated relatives, such mice are more susceptible to colitis, a type of intestinal inflammation, and to asthma, the researchers have now found. In their lungs and intestines, the germ-free mice also harbor an unusually large number of invariant natural killer T (iNKT) cells. These immune cells trigger inflammation after sensing certain microbes or particular molecules, called antigens, made by the body.

The new study suggests that these cells are crucial for conditions such as colitis and asthma. Blumberg and colleagues discovered that genetically altered mice that lack iNKT cells are not prone to colitis, even if they are raised germ-free in sterile surroundings. Furthermore, Blumberg’s team could largely prevent the development of colitis in germ-free mice that do have iNKT cells if they treated the rodents with an antibody that blocks the cells’ ability to detect antigens.

By shifting germ-free mice to cages containing ordinary rodents that teem with bacteria, the researchers demonstrated the importance of early microbe exposure for the distribution of iNKT cells. Transferred mice quickly pick up intestinal bacteria from their cage mates. Moving adult germ-free animals did not reduce the number of iNKT cells in the colon. However, when the researchers rehoused pregnant germ-free mice, ensuring that their offspring would be immersed in bacteria from birth, the pups had fewer iNKT cells in the colon, even after they grew up, Blumberg and colleagues discovered. “It became clear from the study that [iNKT cells are] sensing the composition of the microbial community in the gut and responding to it,” Blumberg says.

Further Reading:

[Science] Torsten Olszak et al., “Microbial Exposure During Early Life Has Persistent Effects on Natural Killer T Cell Function”. Subscription required.

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