Where did this claim come from?
Bioma is an example of a company that sells “personalized” probiotic formulations, determined by taking a quiz about how much weight you want to lose, what kind of food you eat, and your activity levels. It claims to use the results of the quiz to tell which formulation you need. I stopped here… but apparently they only have one formulation (!).
The misconception here is that specific gut microbes can control things like weight, fat distribution, and appetite in very specific ways, and that taking specially targeted supplements of these specific gut microbe populations can fix problems with weight, appetite and fat distribution.
The kernel of truth
Microbes do influence many functions of the body, mostly clearly gut and metabolic system (liver, pancreas etc) health and immune system regulation. The major mechanisms of these benefits seem, so far, to result from substances such as butyrate (short chain fatty acid that nourishes gut cells, regulates immune cells, and may influence gene expression) vitamins, and neurotransmitters such as serotonin and acetyl choline (Chakraborty 2024). Probiotics that contain microbes that produce butyrate, or more reliably, prebiotics or diets that support butyrate producing microbes do seem to have beneficial effects on conditions related to inflammation or immune dysregulation.
Extrapolation beyond reality
Specific benefits, such as reducing “cellulite” or flattening your stomach, or even more general benefits such as weight loss, cannot be linked reliably or specifically to any microbes right now.
Most of the in vivo reports, for instance, are based on findings from mostly mouse studies, in which specific probiotic stains had specific effects on e.g. bone, muscle and fat. Unfortunately, mice are not as good of models for humans as many would hope. Results from human studies are thin on the ground, and do not reliably support beneficial effects of specific probiotics (Huber 2023).
In general, such studies so far only address weight loss and are both few and variable in their methodology (Hamed Rivera 2024). Further, the studies described in a recent review (Alvarez 2021), for instance, reported very short treatment periods (8-12 weeks) so it is unknown whether any benefits from the probiotics were maintained. And if you look at the data (not just the statistics) you see the effect sizes are small, for example 0.64 kilograms, which is about 1.5 pounds (Hamed Rivera 2024). This is actually not very impressive.
The challenge for any intervention is that weight, fat distribution, appetite, etc. are regulated in complex ways, including genetic ways. Yes, certain classes of microbes may, based on the molecules they produce, support beneficial outcomes. But the outcomes are general, such as reductions in inflammation and the consequent “sickness syndrome” of mood symptoms, fatigue, and cognitive “fuzziness”. Importantly, we don’t really know what the mechanisms actually are for any benefits of any specific strain, so it’s hard to know how real the findings are. Beware of any program promising a probiotic formula “tailored for you!”, because the science isn’t there. On the other hand, any program that encourages consumption of a variety of pre- and probiotic foods will support the classes of gut microbes for whom there is an evidence base of general benefits, such as reduced inflammation and improved glucose tolerance, is likely to be legitimate.