I was surprised to find a literature review about probiotics which suggested they may have significant CNS effects. The tl;dr of the review seems to be: 1) You want doses of at least 109 or 1010 CFU, and 2) You want, in particular, the strains B. longum, B. breve, B. infantis, L. helveticus, L. rhamnosus, L. plantarum, and L. casei.
I then sorted the top 15 results on Amazon for “probiotic” by these desiderata, and found that this one seems to be best.
Some points of uncertainty:
Probiotic manufacturers generally don’t disclose the strain proportions of their products, so there’s some chance they mostly include e.g. whatever’s cheapest, plus a smattering of other stuff.
One of the reviewed studies suggests L. casei may impair memory. I couldn’t find a product that didn’t have L. casei but did have at least 109 CFU of each other recommended strain, so if you take the L. casei/memory concern seriously your best option might be combining this and this.
For convenience, here’s a slightly edited-for-clarity version of the abstract:
38 studies (all randomized controlled trials) were included: 25 in animals and 15 in humans (2 studies were conducted in both). Most studies used Bifidobacterium (eg, B. longum, B. breve, and B. infantis) and Lactobacillus (eg, L. helveticus, and L. rhamnosus), with doses between 109 and 10^10 colony-forming units for 2 weeks in animals and 4 weeks in humans.
These probiotics showed efficacy in improving psychiatric disorder-related behaviors including anxiety, depression, autism spectrum disorder (ASD), obsessive-compulsive disorder, and memory abilities, including spatial and non-spatial memory.
Because many of the basic science studies showed some efficacy of probiotics on central nervous system function, this background may guide and promote further preclinical and clinical studies. Translating animal studies to human studies has obvious limitations but also suggests possibilities. Here, we provide several suggestions for the translation of animal studies. More experimental designs with both behavioral and neuroimaging measures in healthy volunteers and patients are needed in the future.
Possibly another good example of scientists failing to use More Dakka. The mice studies all showed solid effects, but then the human studies used the same dose range (10^9 or 10^10 CFU) and only about half showed effects! Googled for negative side effects of probiotics and the healthline result really had to stretch for anything bad. Wondering if, as much larger organisms, we should just be jacking up the dosage quite a bit.
On the other hand: half of mouse studies working in humans is an extremely good success rate. We should be quite suspicious of file-drawer effects and p-hacking.
I agree the effect is consistent enough that we should be suspicious of file drawer/p-hacking—although of course that’s also what you’d expect to see if the effect were in fact large—but note that they were different studies, i.e. the human studies mostly weren’t based on the non-human ones.
I was initially very concerned about this but then noticed that almost all the tested secondary endpoints were positive in the mice studies too. The human studies could plausibly still be meaningless though.
Has anyone (esp you Jim) looked into fecal transplants for this instead, in case our much longer digestive system is a problem?
Turns out there’s an app (Apple, Android) which compiles evidence from 179 studies on probiotics, ranks them by strength of evidence (study design, etc.) then suggests the most evidence-supported probiotic for a given “indication” (allergies, IBS, etc.). The only available CNS-related indication is “Mood/Affect”, though, and the review described in the OP isn’t included in the study database, nor were any of the three studies included in that review that I spot-checked. But the two strains it recommends for mood/affect (b. longum and l. helveticus) are among the seven strains recommended in the OP.
Note that from what I can tell about the state of this field, “most evidence-supported intervention” should be read more as “better than choosing randomly, I guess” than “this is definitely promising.”
So apparently Otzi the Iceman still has a significant amount of brain tissue. Conceivably some memories are preserved?
TIL that (according to this study, at least) adenovirus serotype 36 is present in 30% of obese humans, but only 11% of non-obese humans. The virus appears to cause obesity in chickens, mice, rats and monkeys. It may work (paper, pop summary) by binding to and permanently activating the PI3K enzyme, causing it to activate the insulin signaling pathway even when insulin isn’t present.
Previous discussion on LessWrong.