Transforming gastrointestinal health with probiotic fermented milk: a systematic review and meta-analysis

Fermented milk contains probiotics, which are known for their health benefits. This study explored the effects of probiotic-enriched fermented milk on defecation frequency and gut microbiota, an area previously lacking sufficient evidence. This study included 15 randomized controlled trials retrieved from the Cochrane Library, Embase, and PubMed databases from inception to August 3, 2023. Eligible studies involved adult participants who consumed probiotic-enriched fermented dairy products, with outcomes related to defecation patterns. Data were extracted and pooled using a random-effects model to estimate the overall effect. This study was registered with PROSPERO (CRD42023420924). The meta-analysis involving 882 individuals demonstrated that probiotics-enriched fermented milk significantly increased defecation frequency (mean difference [MD] = 0.79 times/week, 95 % confidence interval [CI]: 0.19–1.39) compared with the control. Healthy individuals significantly improved defecation frequency (MD = 1.18, 95 % CI: 0.08–2.28) when they consumed products enriched in Lactobacillus spp. using starter culture–fermented within 4 weeks, and eventually increased viable count Lactobacillus spp. (MD = 0.66, 95 % CI [0.03, 1.28]). Participants with constipation symptoms showed improved defecation frequency when the intervention lasted for more than four weeks. Stool consistency improvement was greater among participants who consumed probiotic-enriched fermented milk compared to those who consumed placebo products (MD = −0.24, 95 % CI [−0.44, −0.04]). In conclusion, probiotic-enriched fermented milk improved defecation frequency and stool consistency in adults. The effects varied between healthy individuals and those with constipation symptoms, depending on the duration of the intervention, the type of bacterial strain used, and the comparator applied.