“There is one published study of gut microbiota in schizophrenia. Shen and colleagues found a significant reduction in butyrate producers in people with schizophrenia compared to healthy controls. The purpose of this study is to examine changes in serum butyrate levels with the prebiotic: Prebiotin (12g/day), an oligofructose-enriched inulin (FOS); the effect of FOS on the composition of the gastrointestinal microbiota in people with schizophrenia; and the relationship of the composition of the gut microbiota to various clinical, cognitive, and neuroimaging variables.”
Butyrate is made in the gut, you can also get it from food, like butter.
The gut microbiota have been shown to: a) produce multiple neurotransmitters, including gamma-aminobutyric acid (GABA), dopamine, norepinepherine, and serotonin, and may regulate CNS levels of these neurotransmitters; b) modulate brain development through the regulation of synaptogenesis; and c) modulate the levels of stress hormones during brain development, which may affect stress response and anxiety behavior. Moreover, the gut microbiota effects the production of neurotrophins, including brain-derived neurotrophic factor (BDNF), which plays a significant role in neurogenesis and synaptic plasticity (Sudo et al, 2004; Nemani et al, 2015).
The gut microbiome may also affect brain development and function through its regulation of immune system function, which is mediated, in part, through the production of short-chain fatty acids (SCFA). There are three major SCFAs: butyrate, propionate, and acetate. Butyrate is of particular interest, since it plays a key role in maintaining gut homeostasis and epithelial integrity "
The supplement they are using is available to the public, it’s called Prebiotin. The usual dosage is 2-4 grams once or twice a day, but for this study they are using 12 grams. That sounds like a lot but most people should be getting at least 20 grams a day of fiber and a range of 25-40 is considered good.
If you care to read about the trial, it is on clinicaltrials.gov, number NCT03617783