Benefits
More frequent bowel movements in adults with infrequent stools
In a placebo-controlled trial in healthy Japanese adults who had about 3 to 5 bowel movements a week, 25 mg a day for 2 weeks raised bowel movements to 5.0 a week versus 4.3 on placebo, and days with a bowel movement to 4.6 versus 4.1. It was a single trial run by the maker and lasted only 2 weeks.
Stool amount in adults with infrequent stools
Stool amount, a co-primary measure that participants counted in daily diaries, rose more from baseline on the strain than on placebo, but stool amount during the intake weeks was not significantly different between groups. Stool shape, color, odor and the feeling after a bowel movement did not differ.
Water loss through arm skin in women
In 58 women with higher skin water loss, 50 mg a day for 8 weeks reduced water loss through arm skin more than placebo at week 4, but not at week 8, and not on the cheek. Skin hydration did not differ at either site. Self-rated facial flakiness improved at week 4, while elbow roughness and flaking were rated worse at week 8.
Tolerated at 250 mg a day for 4 weeks in a small safety study
In an open-label safety study, 11 healthy adults took 250 mg a day, five times the skin trial dose, for 4 weeks. Six mild events in 2 people (colds, a headache, shoulder stiffness) were judged unrelated, and small shifts in some blood values were judged not clinically meaningful. There was no placebo group.
Heat-killed cells with no live count to maintain
Because the cells are killed by heat and dried, there is nothing alive to die off in storage and nothing that can colonize the gut. That is a point about the format rather than a health result, and no study cited here compared this preparation with live L. casei.
Mechanism of action
Proposed serotonin signaling in the colon
The bowel trial authors described unpublished mouse data in which oral heat-killed strain 327 raised expression of Tph1, the enzyme that starts serotonin production, in colon lining cells and raised serotonin in colon tissue. Serotonin helps trigger gut muscle contractions. The data are unpublished and were not measured in people, so this remains a hypothesis.
Bacterial recognition by gut lining cells
Hormone-producing cells in the gut lining carry Toll-like receptors that recognize bacterial components. The authors propose that dead cells of strain 327 survive digestion and signal through such receptors, and may also shift gut bacteria. They state that further studies are needed, and no human study cited here measured this.
A gut and skin link is proposed, not shown
The skin trial authors note that some live lactic acid bacteria products have been linked to skin changes through lower production of phenols by gut bacteria. They state that whether heat-killed strain 327 works in a similar way still needs to be studied.
Clinical trials
Randomized, double-blind, placebo-controlled, parallel-group trial: one tablet with 25 mg of heat-killed strain 327 (about 50 billion cells) or a matching placebo tablet daily for 2 weeks, May to September 2017, registered as UMIN000027398. Three of the four authors were Kameda Seika employees and Kameda Seika made the tablets; the paper gives no separate funding statement (Saito et al. 2018, Biosci Microbiota Food Health)
104 healthy Japanese adults aged 20 to 64 with about 3 to 5 bowel movements a week, chosen from 397 applicants. 95 were analyzed (50 active, 45 placebo) after 9 were excluded from the efficacy analysis (2 active, 7 placebo).
Primary outcomes: bowel movement frequency was higher on the strain (5.0 vs 4.3 a week, p = 0.020; change from baseline 1.3 vs 0.7, p = 0.025), and stool amount rose more from baseline (p = 0.033), although the intake-period value did not differ significantly. Secondary: days with a bowel movement were higher (p = 0.024); stool shape, color, odor and feeling after a bowel movement did not differ. Both groups improved, a placebo response the authors acknowledged. Mild adverse events occurred in 9 active and 6 placebo participants, none judged related.
Randomized, double-blind, placebo-controlled, parallel-group trial: two tablets a day with 50 mg of heat-killed strain 327 (about 100 billion cells) or placebo for 8 weeks, September 2015 to January 2016, registered as UMIN000018976. Funded by Kameda Seika, which employed four of the seven authors (Saito et al. 2017, Biosci Microbiota Food Health)
64 healthy Japanese women aged 20 to 64 with relatively high skin water loss and about 3 to 5 bowel movements a week; 58 were analyzed (30 active, 28 placebo).
Primary outcomes were water loss and hydration at the cheek and upper arm. Arm water loss fell more than on placebo at week 4 (p = 0.021) but not at week 8 (p = 0.074); cheek water loss and skin hydration at either site did not differ at any visit. In the secondary questionnaire, facial flakiness improved at week 4, but elbow roughness and flaking scored worse than placebo at week 8. Mild adverse events occurred in 14 active and 12 placebo participants, none judged related.
Open-label safety study with no control group: 250 mg a day (about 500 billion cells) for 4 weeks, April to July 2016, funded by Kameda Seika and reported in the same paper as the skin trial (Saito et al. 2017, Biosci Microbiota Food Health)
11 healthy Japanese adults (6 men, 5 women) aged 20 to 64.
Six mild adverse events in 2 people (a headache, a cold, three episodes of cold symptoms and shoulder stiffness) were judged unrelated. Some values shifted slightly from baseline, including white blood cell count, LDL and HDL cholesterol and blood pressure, and all were judged not clinically significant. Eleven people over 4 weeks is too few to detect uncommon effects.