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

Sixty-six healthy Saudi young adults with moderate to high perceived stress completed this trial, 37 taking Lactobacillus rhamnosus GG at 6 billion CFU daily for 30 days and 29 receiving no intervention. Stress score reductions were significantly greater with the probiotic (p = 0.006), and endline stress scores were lower (14.81 vs 19.48, p = 0.003), with adjusted models showing controls scoring 3.79 points higher (95% CI 0.74-6.83, p = 0.016). The effect was significant in men (p = 0.007) but not women (p = 0.341). There were no differences between groups in bowel movement frequency, stool consistency or digestive symptoms — a null result on gut function.