We investigated the effects of Lactobacillus paragasseri OLL2716 on gastrointestinal symptoms in healthy adults with gastric complaints. In this randomized, double-blind, placebo-controlled trial, 174 healthy Japanese adults were randomly assigned to an OLL2716 or placebo group, and each group consumed 85 g of yogurt containing L. paragasseri OLL2716 or placebo yogurt daily for 12 weeks. The primary endpoint was the change in gastric symptoms from baseline as per the participants’ questionnaires at 6 and 12 weeks. The secondary endpoints were changes from baseline in the short-form Nepean Dyspepsia Index (SF-NDI), the Gastrointestinal Symptom Rating Scale (GSRS), and the Council on Nutrition Appetite Questionnaire-Japanese (CNAQ-J) scores at 6 and 12 weeks. The primary endpoint data showed that the changes in “epigastric pain” at 6 and 12 weeks were significantly decreased in the OLL2716 group compared with those in the placebo group. Additionally, the changes in “epigastric pain syndrome-like symptoms” were significantly decreased in the OLL2716 group compared with those in the placebo group at 6 weeks. The SF-NDI items that improved at 6 weeks were “irritable, tense, or frustrated”, “enjoyment of eating or drinking”, and “tension”, which are sub-scales related to mental stress. The items “Over-all” in the GSRS and “feeling hungry” in the CNAQ-J significantly improved in the OLL2716 group compared with the placebo group at 12 weeks. The results suggest that regular intake of L. paragasseri OLL2716 may improve both gastric discomfort and mental stress in healthy adults with gastric complaints, such as postprandial fullness or early satiety.

The significance of less abundant genera within the gut microbiota, such as Parabacteroides, remains largely unexplored. Despite its low levels, Parabacteroides is highly conserved and potentially beneficial across populations. This trial aimed to evaluate whether a four-week intake of glucolacto-oligosaccharides (GLO), previously reported as an enhancer of Parabacteroides, improves defecation frequency as the primary outcome. It also assessed holistic gut health and underlying microbiota-based mechanisms. In this randomized, double-blind, placebo-controlled trial, 50 healthy Japanese participants with a defecation frequency of five or fewer times per week were enrolled. The mean (±SE) weekly defecation frequency in the GLO group was 3.2 ± 0.2 at baseline, increasing to 5.8 ± 0.6 at week 4, whereas that in the placebo group was 3.4 ± 0.3 at baseline, increasing to 4.4 ± 0.3 at week 4. The time-dependent weekly defecation frequency was significantly higher in the GLO group than in the placebo group (p = 0.029). Changes in the relative abundance of the genus Parabacteroides significantly increased in the GLO group compared with in the placebo group. Changes in fecal bile acid composition were also confirmed in the GLO group compared with the placebo group, which was thought to be due to the unique features of Parabacteroides. Furthermore, changes in alpha diversity indices were significantly higher in the GLO group than in the placebo group (Simpson, p = 0.041; Pielou, p = 0.022). Additional analysis demonstrated that the increase in alpha diversity in the GLO group was significantly correlated with the increase in the relative abundance of Parabacteroides (p = 0.006), which tended to be associated with decreases in serum gamma-glutamyltransferase (p = 0.089) and serum triglyceride (p = 0.075) levels. These data suggest that GLO intake improved defecation status, selectively increased Parabacteroides, and harmonized the gut environment.