Yeast mannan (YM) is an indigestible water-soluble polysaccharide of the yeast cell wall. In vitro fecal fermentation studies showed that YM could exhibit a notable prebiotic effect. The aim of this randomized, double-blind, placebo-controlled study was to assess the efficacy of YM intake on the intestinal environment and skin condition. One hundred and ten healthy female subjects aged 30–49 years were supplemented with YM or placebo for eight weeks. Skin dryness was set as the primary endpoint. No side effects were observed during the study. Microbiota analyses revealed that YM intake selectively increased the relative abundance of Bacteroides thetaiotaomicron and Bacteroides ovatus compared to that by placebo. Feces and urine analyses showed that YM intake lowered the concentration of fecal p-cresol, indole, and skatole, and elevated urinal equol levels compared to those in placebo. Furthermore, YM supplementation ameliorated subjective skin dryness. This study suggests that YM intake could promote beneficial Bacteroides and improve the intestinal environment and skin condition.

Probiotic-fermented milk is commonly used to maintain intestinal health. However, the effects of heat-treated fermented milk, which does not contain live microorganisms, on intestinal function are not yet fully understood. This study aimed to investigate whether heat-treated Lactobacillus helveticus CP790-fermented milk affects fecal microbiota and gut health as a “postbiotic”. A randomized, double-blind, placebo-controlled trial was conducted in healthy Japanese individuals aged 20–59 years with a tendency toward constipation. Participants consumed 100 mL of either the test beverage (n = 60) or placebo beverage (n = 60) for four weeks. The test beverages were prepared with heat-treated CP790-fermented milk, while the placebo beverages were prepared with nonfermented milk flavored with lactic acid. Fecal samples were analyzed using 16S rRNA gene sequencing. Constipation symptoms were assessed using defecation logs and the Patient Assessment of Constipation Symptoms (PAC-SYM) questionnaire. Mood state was also assessed using the Profile of Mood States 2 (POMS2) questionnaire to explore its potential as a “psychobiotic”. Desulfobacterota were significantly decreased by CP790-fermented milk intake. PICRUSt2 analysis predicted a decrease in the proportion of genes involved in the sulfate reduction pathway following the consumption of CP790-fermented milk. The CP790-fermented milk intervention significantly improved stool consistency and straining during defecation. These improvements were correlated with a decrease in Desulfobacterota. After the intervention, overall mood, expressed as total mood disturbance, and depression–dejection were significantly better in the CP790 group than in the placebo group. These results suggest that the intake of CP790-fermented milk could be effective in modulating gut microbiota and improving constipation symptoms and mood states.

Human gut health is closely related to sleep. We aimed to evaluate the efficacy of yeast mannan (YM) in improving bowel habits and sleep quality, along with metabolomics in fecal samples. A total of 40 healthy adults (age range, 22–64 years) with discomfort in defecation were enrolled and randomly allocated to receive either YM (n = 20; 1.1 g/day) or placebo (n = 20) for four weeks. Participants recorded their defecation habits throughout the test periods. Sleep electroencephalogram (EEG) recording using an EEG device and fecal sampling were performed pre- and post-treatment. The YM group significantly increased defecation frequency and stool volumes compared to the placebo group. After 4 weeks of treatment, the non-REM sleep stage 3 (N3) duration in the YM group was significantly higher than that in the placebo group. YM ingestion significantly lengthened total time in bed (TIB) and significantly shortened N3 latency compared to placebo intake during the trial. The metabolomics analysis found a total of 20 metabolite differences between the YM and placebo groups. As a result of stepwise linear regression, changes in fecal propionate and gamma-aminobutyric acid (GABA) levels were identified as the primary factors explaining changes in TIB and N3 latency, respectively. Our findings suggest that the prebiotic YM could be beneficial to gut health and sleep quality.

Background: Gut health and brain activity are closely linked, and the gut−brain axis plays a crucial role in regulating mental health. Interventions using beneficial microbes, such as probiotics and postbiotics, are gaining attention as promising approaches to support mental health. This study aimed to evaluate the effects of postbiotic heat-treated Lactobacillus gasseri CP2305 (CP2305) on mental stress and alpha oscillatory activity in the brain. Methods: This double-blind, randomized, crossover, placebo-controlled study included 28 healthy participants aged 20–44 years. The participants underwent two trial sessions and consumed a single dose of tablets containing heat-treated CP2305 (postbiotic; 1 × 10 ¹⁰ cells) or matching placebo tablets. In each session, electroencephalography (EEG) at eight positions was recorded from before to 60 min after ingestion to measure the alpha power. Heart rate variability was also recorded to calculate the root mean square of successive differences (RMSSD), an indicator of parasympathetic activity. The effects on mental state were evaluated using the visual analog scale (VAS) and Profile of Mood States, 2nd edition (POMS2). An in vitro study was conducted using the enterochromaffin cell line RIN14B to measure serotonin (5-HT) secretion levels following the heat-treated CP2305 administration. Results: The alpha power showed a significantly greater increase from baseline following consumption of heat-treated CP2305 compared with the placebo. The change in the RMSSD from baseline was significantly greater following consumption of heat-treated CP2305 than following the placebo. Both the mental stress VAS and POMS2 tension–anxiety scores showed significantly greater improvements following consumption of heat-treated CP2305 compared with the placebo. In the in vitro 5-HT assay, extracellular 5-HT levels were significantly higher under the heat-treated CP2305 condition than under the control condition. Conclusion: This is the first clinical study to examine the effects of postbiotics on alpha oscillatory activity in the brain. Heat-treated CP2305 consumption was associated with modulation of brain activity, enhancement of parasympathetic activity, and alleviation of stress, indicating its potential as a functional food ingredient for mental health support. These beneficial effects may be partly associated with alterations in gut-derived 5-HT signaling induced by heat-treated CP2305. However, further studies are required to elucidate the underlying mechanisms. Clinical trial registration: https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000064175 , Identifier UMIN000056164.