Source
Forssten et al. (2022), LIT-915, “One Giant Leap from Mouse to Man”, read in full in NOTE-703 from the Europe PMC text. The authors were all employed by IFF Health & Biosciences, which “manufactures and commercializes probiotics”. The review is narrative, with no search method.
What was actually shown
Routes, in animals. “The vagus nerve is the most direct route of communication between the gut and the brain”. In mice the effects are lost after vagotomy. Germ-free animals show an exaggerated stress-hormone response that colonisation normalises, replicated across rodent strains.
Transplant. Faecal transplant from depressed humans to rodents gives abnormal behaviour “indicating at least partial transfer of the clinical psychiatric phenotype”. The donors were few, and “the gut microbiome is the only humanized component of the rodent”.
People. “A recent meta-analysis demonstrated that probiotic consumption could result in a reduction of subjective stress levels in healthy volunteers”. Single trials report reduced reactivity to sad mood, perceived stress and anxiety, some only under stress or in subgroups.
Failures. L. rhamnosus JB-1, after “comprehensive preclinical evidence”, “was not found to have an effect on mood, anxiety, stress, sleep quality, memory performance, attention, or anti-inflammatory cytokine levels compared with the placebo.” Another strain did not relieve exam stress. A combination left depression scores identical to placebo.
What could have come out otherwise. The strains with the best rodent records could have worked in people. The trials the review reports say they did not.
What this does not say
- That probiotics treat depression. The evidence is small trials and nulls (C4, weak). The authors note that “most findings from these clinical trials cannot be extrapolated to patients with clinically diagnosed depression.”
- That one’s own microbiome moves everyday mood. In people the evidence is about adding strains, mostly in healthy volunteers, with small effects on subjective stress.
- That the routes are shown in humans. Vagal, immune and endocrine signalling are documented in animals and asserted in humans (C1).
- That the review is complete. It has no search method, and its optimistic close is warmer than its own failures warrant (NOTE-703).
Connections
- The owner’s claim that a lower-level collective within the person can at times drive behaviour and experience (CLAIM-166) is grounded in this reading and in LIT-903 (gut metabolites and appetite). This account states what CLAIM-166 relied on for affect: drive from below is causal in rodents and modest in people.
- The vagus is an interoceptive channel, so this is a route from the microbiome into the bodily state that, on THEORY-045, felt affect reports. That bearing is the record’s, not the review’s.
Note of 2026-10-29: what holds it back
Kept Proposed by the sixteenth status review. NOTE-703 read the review in full, but it is a narrative review without a search method, by a probiotics manufacturer’s staff, and its human half rests on one meta- analysis of healthy volunteers and trials it selected. No independent systematic review of placebo-controlled psychobiotic trials, separating healthy from depressed participants and subjective from objective outcomes, is in the record. Narrowing to the rodent half would free nothing: CLAIM-166 uses both halves.