Additional studies are needed before medical laboratory tests for ‘lean’ microbes can be developed for use by physicians treating overweight and obese patients

Researchers at Cornell University have identified a family of microbes that may provide a genetic explanation for why some people are able to stay thin. If their findings are validated, a clinical laboratory test for these bacteria, and a macrobotic regiment to help people lose weight or stay lean, could be down the road.

Emerging Field Involving the Human Microbiome

The Cornell study was published in November 2014 in the journal Cell. It spotlights one bacterial taxon, the family Christensenellaceae, which was only named in 2012. That makes it a relatively new subject for researchers in the booming human microbiome sector.

Ruth Ley, Ph.D., is a Cornell University Associate Professor of Microbiology, and the research paper’s senior author. She believes the new Cornell study makes clear the connection between the human genotype and health-associated gut bacteria.

Ruth Ley, Ph.D.

Ruth Ley, Ph.D., an Associate Professor at Cornell University, says the Cornell-led study establishes the link between the host genotype and gut microbiome, which may help explain why some people can stay thin (Photo copyright Cornell University)

“If you look across the population [of gut bacteria] and explain abundances, there is a host genetic component,” Ley said in a Cornell University news release. “Up until now there had been no direct evidence that anything in the human gut is under that kind of [genetic] influence.”

Identical Twins Share More Gut Microbiotas than Fraternal Twins

The Cornell team examined more than 1,000 fecal samples obtained from the TwinsUK registry, including 416 twin pairs. They found that twins raised in the same households shared environmental influences but not necessarily gut bacteria. Identical twins, who have the same genetic makeup, had more similar gut microbiotas to each other than did fraternal twins, who share half the same genes. In all twins, lean individuals had higher levels of the highly heritable taxon Christensenellaceae than obese ones.

In addition to identifying many microbes, such as Christensenellaceae and its partners, that were enriched in people with low body mass index, researchers were able to reduce weight in germ-free mice by introducing the gut bacteria Christensenellaceae minuta.

Calls for More Research

While the Cornell study is one of the first to show that genetics plays a role in the bacteria that regulate weight gain, the scientific community says more research is needed to prove a connection between specific bacteria and weight gain.

“The genetic association is clear,” said Patrice Cani, Ph.D., a leader of the Metabolism and Nutrition Research Group at Université Catholique de Louvain for The Scientist magazine. “The impact of these bacteria on body weight is less clear.”

Ley told the Wall Street Journal (WSJ) that the Cornell researchers’ next step is to give the Christensenellaceae bacteria to mice orally and study how long the effects on weight gain last. In their initial work, germ-free mice that were given fecal transplants of the bacteria weighed less than the untreated control group of mice after 21 days.

Good Bacteria Products Might Be on Store Shelves One Day

If additional studies validate the Christensenellaceae bacteria’s role in human metabolism, medical laboratory testing for these bacteria could be followed by probiotic therapies for weight loss. For now, Ley is unwilling to predict whether weight-reducing probiotics one day will be on store shelves.

“I’m a scientist—I am going to say, maybe,” she said, in the WSJ article.

Tim Spector, a Genetic Epidemiologist at King’s College London, who contributed to the study, says scientists do have to pay more attention to so-called good bacteria.

Tim Spector

Tim Spector, a Genetic Epidemiologist at King’s College London, believes the Cornell study shows the benefits of researching more than just disease-causing bacteria. (Photo copyright King’s College London)

“In the past, the main bacteria we saw were the nasty guys, the ones that kill you. We haven’t been looking at the thousands of nice guys that help and keep us thin,” Spector said in the WSJ article.

Additional Studies Show Weight Gain/Loss in Mice Given Gut Microbes

The Cornell study is not the first research linking the microbes in our guts to the numbers on our bathroom scales. A landmark 9-year study published in the journal Nature found that lean and obese individuals differed “by the number of gut microbial genes and thus gut bacterial richness,” with the lean group less likely to gain weight over time or develop common chronic diseases.

In September 2013, a study published in Science showed germ-free mice on identical diets put on weight when they were transplanted with gut microbes from an obese person, but not from a lean person.

Assume that this research progresses to the point where the clinical community accepts that certain types of human microbiomes result in leaner individuals. It is probable that such knowledge would lead to clinical laboratory tests that physicians would use to manage overweight and obese patients. That would be a source of value for medical laboratories, but it would not be the end of the story.

If the public were to eventually believe that a certain microbiome was associated with lean individuals, many people would want to use direct access testing (DAT) to do their own microbiome analysis, followed by a trip to the health food store to purchase the macrobiotic regiment they believe would set them on the course to lose weight. In this scenario, clinical labs could generate additional cash sales by offering these types of DAT services.

—Andrea Downing Peck

Related Information:

Gut Microbiome Heritability

Expanding Knowledge about the Human Microbiome Will Lead to New Clinical Pathology Laboratory Tests

Genes Influence Types of Microbes in Human Gut

Effort to Map Human Microbiome Will Generate Useful New Clinical Lab Tests for Pathologists 

Lack of Gut Bacteria Can Make You Overweight

Mayo Clinic and Whole Biome Announce Collaboration to Research the Role of the Human Microbiome in Women’s Diseases Using Unique Medical Laboratory Tests

Richness of Human Gut Microbiome Correlates with Metabolic Markers 

Microbiologists at Weill Cornell Use Next-Generation Gene Sequencing to Map the Microbiome of New York City Subways 

Gut Microbiota from Twins Discordant for Obesity Modulate Metabolism in Mice 

At the University of Michigan, Research Study Indicates how Composition of Gut Microbiome May Serve as Complementary, Noninvasive Screening Tool for Colon Cancer