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.
“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.
“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