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Tag: gut microbiome

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This research illustrates how little we currently know about gut bacteria.But it did show the importance of diet. From Science Daily:

Monitoring rise and fall of the microbiome

Trillions of bacteria live in each person's digestive tract. Scientists believe that some of these bacteria help digest food and stave off harmful infections, but their role in human health is not well understood.

To help shed light on the role of these bacteria, a team of researchers led by MIT associate professor Eric Alm recently tracked fluctuations in the bacterial populations of two research subjects over a full year. The findings, described in the July 25 issue of the journal Genome Biology, suggest that while these populations are fairly stable, they undergo daily fluctuations in response to changes in diet and other factors...."To a large extent, the main factor we found that explained a lot of that variance was the diet."

There are a few thousand strains of bacteria that can inhabit the human gut, but only a few hundred of those are found in any given individual, Alm says. For one year, the two subjects in the study collected daily stool samples so bacterial populations could be measured. They also used an iPhone app to track lifestyle factors such as diet, sleep, mood, and exercise, generating a huge amount of data.

Analysis of this data revealed that dietary changes could produce daily variations in the populations of different strains of bacteria. For example, an increase in fiber correlated with a boost in the populations of Bifidobacteria, Roseburia, and Eubacterium rectale. Four strains -- including Faecalibacterium prausnitzii, which has been implicated in protecting against inflammatory bowel disease -- were correlated with eating citrus.

During the study, each of the two subjects experienced an event that dramatically altered the gut microbiome. Subject B experienced food poisoning caused by Salmonella, and Subject A traveled to a developing nation, where he experienced diarrheal illness for two weeks.

During Subject B's infection, Salmonella leapt from 10 percent of the gut microbiome to nearly 30 percent. At the same time, populations of bacteria from the phylum Firmicutes, believed to be beneficial to human health, nearly disappeared. After the subject recovered, Firmicutes rebounded to about 40 percent of the total microbiome, but most of the strains were different from those originally present.

Subject A also exhibited severe disruptions to his microbiome during his trip, but once he returned to the United States, it returned to normal. Unlike Subject B's recovery from food poisoning, Subject A's populations returned to their original composition.

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If you missed these recent articles about weight and gut bacteria, please go read them now. Amazing stuff. From the December 9, 2013 Washington Post:

The microbes in your gut may be making you fat or keeping you thin

 ...a growing body of evidence suggesting that naturally occurring bacteria and other microbes in the body, and possibly even viruses, can influence weight in ways that scientists are only just beginning to understand. Numerous studies are underway looking at the role of intestinal organisms in obesity, with a focus on how they extract energy from food and how this affects weight gain or loss.

From September 5, 2013 Science News: Gut infections keep mice lean

Skinniness could be contagious. Gut bacteria from thin people can invade the intestines of mice carrying microbes from obese people. And these invaders can keep mice from getting tubby, researchers report in the Sept. 6 Science.

But the benefits come with a catch. The invading microbes drop in and get to work only when mice eat healthy food. Even fat-blocking bacteria can’t fight a bad diet, suggests study leader Jeffrey Gordon, a microbiologist at Washington University in St. Louis. 

Fat and thin people have different microbes teeming in their intestines, for example. And normal-weight mice given microbes from obese mice pack on extra fat, says coauthor Vanessa Ridaura, also of Washington University.

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Some recent studies have explored the link between bacteria in the gut and colorectal cancer. The beneficial Prevotellaceae bacteria (mentioned in the Nov. 5 study below) have been discussed elsewhere as liking whole grain foods. So go feed your gut with some nice whole grain bread or cereal. And some fruits and veggies while you're at it. As mom used to say: "You are what you eat."

A study published December 6, 2013 found that decreased diversity of the gut microbiome and the presence of certain types of bacteria were associated with colorectal cancer in humans: Decreased Diversity of Bacteria Microbiome in Gut Associated Colorectal Cancer

From the November 5, 2013 Science Daily: Microbes in the Gut Help Determine Risk of Tumors

Transferring the gut microbes from a mouse with colon tumors to germ-free mice makes those mice prone to getting tumors as well, according to the results of a study published in mBio®, the online open-access journal of the American Society for Microbiology. The work has implications for human health because it indicates the risk of colorectal cancer may well have a microbial component.

Scientists have known for years that inflammation plays a role in the development of colorectal cancer, but this new information indicates that interactions between inflammation and subsequent changes in the gut microbiota create the conditions that result in colon tumors.

Known risk factors for developing colorectal cancer include consuming a diet rich in red meat, alcohol consumption, and chronic inflammation in the gastrointestinal tract (patients with inflammatory bowel diseases, such as ulcerative colitis, are at a greater risk of developing colorectal cancer, for instance).

The results were stark: mice given the microbiota of the tumor-bearing mice had more than two times as many colon tumors as the mice given a healthy microbiota. What's more, normal mice that were given antibiotics before and after inoculation had significantly fewer tumors than the mice that got no antibiotics, and tumors that were present in these antibiotic-treated mice were significantly smaller than tumors in untreated mice. This suggests that specific populations of microorganisms were essential for the formation of tumors...

Looking at the microorganisms, they found that tumor-bearing mice harbored greater numbers of bacteria within the Bacteroides, Odoribacter, and Akkermansia genera, and decreased numbers of bacteria affiliated with members of the Prevotellaceae and Porphyromonadaceae families. Three weeks after they were inoculated with the communities from the tumor-bearing mice, the germ-free mice had a gut microbiome that was very similar to the tumor-bearing mice, and they had a greater abundance of the same bacterial groups associated with tumor-formation.