Lactobacillus Casei is in two specialized probiotic drinks: Yakult and DanActive (Actimel) and is also found in fermented green olives and cheddar cheese. There are over 5000 articles on PubMed.

“Administration of lactobacillus casei prior to an inflammatory insult to the bowel prevents the development of increased intestinal permeability.^{[10][11]” that is, it appears to reduce leaky git.}

Lactobacillus casei Shirota Supplementation Does Not Restore Gut Microbiota Composition and Gut Barrier in Metabolic Syndrome: A Randomized Pilot Study[2015].

“We found a significant rise in both Lactobacillus and Bifidobacteria in those taking the LcS, and there was also a significant decrease in anxiety symptoms among those[CFS Patients] taking the probiotic vs controls” [2009] – dosage was 24 Billion CFU, i.e. 4 bottles per day.

Fermented milk containing Lactobacillus casei strain Shirota prevents the onset of physical symptoms in medical students under academic examination stress [2015].

“Lactobacillus casei strain GG alone did not significantly improve symptoms in this irritable bowel syndrome” [2000] Note this is a different strain than above.

The anti-obesity effects of Lactobacillus casei strain Shirota versus Orlistat on high fat diet-induced obese rats[2015].

I recommend Yakult(click for a post on PubMed articles on this strain) because it has been demonstrated to reduce Anxiety levels in CFS. I know CFSers who can notice in a day or two of forgetting to take it that anxieties start building. Stress and anxiety are associated with relapse in CFS, thus reducing the same may decrease the risk of flares.

If you are using a mixture with L.Casei in it, be wary that it may be a “token amount” and far less than the 40 Billion CFU/day used in the above study.