F/B – Biomarker For Weight Issues Or Just Another Marketing Tool?

It is undeniable that the recent discovery of the human microbiome has been a game changer in terms of our understanding of health. However, as with any early discovery the hype about all the potential profits it can bring is present as well. This inevitably attracts all types of interests. The microbiome space being new and promising makes launching and selling products easier to implement. As our world is getting sicker, people are looking in any place that will offer a flicker of hope. Thus, it is easy for certain companies to cherrypick a few scientific papers on a topic where consensus has not yet been reached and use them to their advantage.

The current research effort is mainly focusing on finding certain microbial signatures of dysbiosis that will serve as an alert to the onset of specific diseases. This is nothing groundbreaking as it follows the same structure as the rest of modern medicine — doctors run diagnostic tests and figure out what drugs patients should take to get their numbers within the reference range. It is a tried and tested structure and makers of home stool and vaginal tests have decided to follow the same pattern. One of the potential biomarkers from a home stool test that has gained popularity is the F/B ratio. Here, F stands for the relative abundance of Firmicutes, and B stands for the relative abundance of Bacteroidetes in the gut. Firmicutes & Bacteroidetes are the most abundant phyla of bacteria in the Western gut. This ratio allegedly provides information on whether the test taker has weight issues and how to fix them. For F/B values it has been proposed that it is best to have this number low – generally smaller than 1 — this is based on some studies (mostly on animals), with the notion that a high F/B ratio is linked to obesity.

Usually, a large reason why a person would order a home stool test is likely because they feel something is off with their health — they are not right in the homeostasis state that they intrinsically know they should be in. Naturally, they are looking for answers, the type of answers that they will not get when they go to their doctor, who likely does not have the time to listen to the details of their malaise, unless it is something very obvious or very serious. Perhaps a home test will point the person in the right direction to solve their discomfort. If a number is off in the test, the idea is to push it back to where it is supposed to be by implementing lifestyle changes or, better yet for the seller of the test, by supplement intake. It is important to note that women are more likely to purchase home stool tests and are also more likely to feel self-conscious of their weight. Therefore, they are more likely to buy supplements that promise to restore this ratio to equilibrium.

When one looks at the academic literature related to F/B ratios, there are a lot of studies that find the evidence inconclusive. There is a very interesting meta-analysis looking at studies from different countries, such as, Thailand, UK, Pakistan, Ukraine, Argentina, USA, Chile, India, etc. that warns that it is “difficult to associate the F/B ratio with a determined health status”. Even further, looking at hunter-gatherer and tribal microbiomes this ratio is very high — 32 in some cases with a lack of any weight issues. See table below:

Obviously, there are many open questions remaining about the F/B ratio. Claiming that it is possibly linked to obesity, while not fully erroneous at the moment due to the hypothetical nature of the statement, is not giving a clear picture of the science. Selling products that change the F/B gut ratio with the implied hope of weight loss is simply wrong. We clearly need more rigorous science and we need a lot more education on the topic so that consumers at the very least do not waste their hard earned money on a product that hopefully is just placebo while at its worst can potentially cause some harm, since its intended purpose is to change a ratio whose meaning is currently not well understood.

As a summary I think this quote by F. Shanahan, MD, a research professor at University College Cork in Ireland, says it best: “The need for precision in communicating microbiome science is amplified by human gullibility to the promise of personal microbiome ‘tests’ and unsupported health claims for microbiota manipulation. This aspect reflects poor capacity for critical thinking, particularly risk and benefit appraisal by consumers.”


• Magne, F. et al. The Firmicutes/Bacteroidetes Ratio: A Relevant Marker of Gut Dysbiosis in Obese Patients? Nutrients 12, 1474 (2020).

• Schnorr, S.L. et al. Gut microbiome of the Hadza hunter-gatherers. Nat. Commun. 5, 3654 (2014).

• Ramadass, B. et al. Faecal microbiota of healthy adults in south India: Comparison of a tribal & a rural population. Indian J. Med. Res. 145, 237-246 (2017).

• Krajmalnik-Brown, R. et al. Effects of gut microbes on nutrient absorption and energy regulation. Nutr. Clin Pract. 2, 201-214 (2012).

• Louis, S. et al. Characterization of the Gut Microbial Community of Obese Patients Following a Weight-Loss Intervention Using Whole Metagenome Shotgun Sequencing. PLoS One 2, 11 (2016).

• Shan Y. et al. Responsible stewardship for communicating microbiome research to the press and public. Nat. Med. 25, 872–874 (2019).

• Lynch S.V., Ng, S.C., Shanahan, F. et al. Translating the gut microbiome: ready for the clinic? Nat. Rev. Gastroenterol. Hepatol. 16, 656–661 (2019).



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