The effect of probiotic supplementation on perceived stress and bowel function in healthy young adults: evidence from a randomized controlled trial in Makkah

Abstract

Background: Young adults experience high, persistent stress due to academic, social, and financial pressures. Lactobacillus rhamnosus GG (LGG) may reduce stress via the gut-brain axis, yet evidence from Middle Eastern populations is limited. We tested whether LGG lowers perceived stress in Saudi young adults and improved bowel function.

Methods: In this randomized controlled trial, healthy adult participants with moderate-high Perceived Stress Scale (PSS) scores received LGG (6 × 10⁹ CFU/day, capsule) for 30 days or no intervention. Validated PSS version, anthropometrics and bowel habits were assessed at baseline and endline. Analyses included paired, two-sample t tests, Wilcoxon rank-sum and multivariable linear regression adjusted for baseline PSS, age, sex, and BMI were conducted.

Results: Sixty-six participants completed the trial (37 probiotic; 29 controls; mean age 21.97 ± 2.59 vs. 20.83 ± 1.91 years). Post-intervention, stress score reductions were significantly greater in the probiotic group than controls (p = 0.006). In sex-stratified analyses, males receiving probiotics showed larger reductions than male controls (p = 0.007), while no significant difference was observed among females (p = 0.341). Probiotic participants also reported lower post-intervention stress scores (14.81 ± 6.12 vs. 19.48 ± 5.91; p = 0.003) and a higher proportion classified as low stress (84.2% vs. 15.8%; p = 0.008). Adjusted models showed control participants had stress scores 3.79 points higher than probiotic recipients (95% CI 0.74-6.83; p = 0.016). No between-group differences were found in bowel movement frequency, consistency, or GI symptom improvement.

Conclusion: A 30-day LGG course may reduce perceived stress-particularly in males-with a trend level effect observed in females without affecting bowel habits. Probiotics may be considered as an adjunct for stress management in high-risk young adult populations. Future larger, placebo-controlled, and longer-term trials are recommended to confirm these findings and explore underlying mechanisms.

Clinical trial registration: This trial is registered at ClinicalTrials.gov (Identifier: NCT06464484; https://clinicaltrials.gov/study/NCT06464484).

Keywords: Saudi Arabia; bowel function; gut–brain axis; perceived stress; probiotics; randomized controlled trial.