Personalized Probiotic Claims

What the research does show

People differ in how probiotics settle in the gut. In a 2018 study combining mice and human volunteers, an 11-strain probiotic stayed viable through the gut. In mice with normal gut microbes it met strong resistance at the gut lining, while humans showed person-, region- and strain-specific patterns. These patterns were predicted by baseline features of the person and their microbiome, but could not be told apart by looking at probiotics in stool. The authors concluded that routine probiotics may be limited in how universally and persistently they affect the gut lining, and that new personalized approaches merit development. [1] Label: promising but limited; this was a small, invasive research study and not a test of health outcomes.

Probiotics can slow recovery after antibiotics in some research. In a second 2018 study, compared with spontaneous recovery, probiotics caused markedly delayed and incomplete return of the person's own gut microbial community, while a person's own stool microbiota given back (autologous transplant) produced rapid recovery. The authors said possible benefits of probiotics after antibiotics may be offset by compromised recovery of the gut lining. [2] This is an argument that one-size-fits-all use deserves study. It is not evidence that a mailed test can select a better product. Autologous transplant is a research procedure and is not something to attempt at home.

Most probiotics do not need to "settle" to act. A 2019 review noted most studies failed to report any impact on the microbiota, and proposed that effects may come from shared genes and metabolites, supporting a challenged microbiota, and influence on gut lining and immune cells. [3]

What "precision probiotics" research is

Researchers are exploring ways to pick or design probiotics using protein and metabolite data and computer models. A 2023 review describes this as a research direction toward "precision probiotics", motivated by the inconsistency of generalized probiotics. [4] That is a field of research, not a proven consumer service.

Do not confuse it with personalized diet research

A separate, better-studied area is personalized nutrition. A 2015 study of an 800-person cohort measured responses to 46,898 meals, found high variability in blood sugar response to identical meals, and built a machine-learning model that included gut microbiota data. A blinded randomized dietary trial based on it produced lower post-meal blood sugar responses. [5] That concerns food and blood sugar, not probiotic selection. See What Is Precision Nutrition?.

What the general probiotic evidence says

The US National Center for Complementary and Integrative Health says that in most instances we still do not know which probiotics are helpful and which are not, how much people would have to take, or who is most likely to benefit. [6] The UK's NHS notes that probiotics are generally classed as food rather than medicine, so they do not go through the rigorous testing medicines do, and that it cannot always be sure a product contains the bacteria stated on the label. [7] Label reading is covered in Probiotic Strains and Labels.

How to read a "personalized probiotic" offer

• Which health outcome improved, in which people, versus what comparison?
• Was the test result used to choose the product in the trial, or only a general probiotic?
• Is a stool result being used to judge the gut lining, when research shows the two can differ? [1]
• Is a disease or "dysbiosis" implied? See Dysbiosis in Research and Marketing.

Without these answers, treat the offer as a marketing claim. More on reading tests: Commercial Stool Tests.