Gastrointestinal issues are fairly common throughout childhood and adulthood, affecting an estimated 8–25% of the general population (1). These percentages may vary based on the specific gastrointestinal condition, and the age of the individuals affected (2). Gastrointestinal disorders, including diarrhea and constipation, are common health concerns worldwide. Diarrhea is a significant global gastrointestinal issue, causing around 500,000 deaths annually in children under five (3). The World Health Organization (WHO) defines diarrhea as the passage of three or more loose or watery stools within a 24-h period (4). The disruption of intestinal microflora is a hallmark of diarrhea and can be triggered by various factors, including antibiotic use, infectious agents, and poor nutrition (5). Diarrhea can cause dehydration and electrolyte imbalances in children and adults, leading to serious consequences such as growth stunting in children, malnutrition, and recurrent enteric infections (6). This impairment is linked to a heightened risk of mortality (3, 7).

Also, constipation, characterized by infrequent and painful bowel movements, abdominal discomfort, and fecal incontinence, poses a major challenge in pediatric and adults healthcare worldwide. The prevalence of this condition is estimated to be between 0.7 and 29.6% worldwide (8). It is a common concern among both children and adults, often causing significant physical discomfort in affected individuals, along with psychological impacts (9). Constipation arises from a combination of factors, including genetic predisposition, disrupted intestinal motility, low dietary fiber and fluid intake, insufficient physical activity, and a diminished urge to defecate (10). Given these impacts of diarrhea and constipation on health and well-being, finding effective interventions is crucial. This is where probiotics come into play, offering a promising approach to managing and alleviating these gastrointestinal issues.

Probiotics have gained widespread recognition for their role in promoting gut health, particularly in preventing and managing gastrointestinal disorders like diarrhea and constipation. Their effectiveness is primarily linked to their ability to restore microbial balance, enhance gut barrier function, and modulate immune responses (11). Probiotics, defined by the World Health Organization as “live microorganisms that, when consumed in adequate amounts, confer health benefits to the host,” have demonstrated efficacy in managing gastrointestinal disorders such as diarrhea and constipation (12, 13). Probiotics exert their effects through a variety of mechanisms, including competitive inhibition of pathogenic bacteria, enhancement of mucosal barrier integrity, modulation of local and systemic immune responses, and production of antimicrobial compounds such as bacteriocins and short-chain fatty acids (14). The therapeutic efficacy of probiotics is strain-dependent. Lactobacillus rhamnosus GG enhances intestinal barrier function and stimulates the production of anti-inflammatory cytokines, while Saccharomyces boulardii has been shown to inhibit pathogen adhesion and increase enzyme activity that aids in nutrient absorption (15).

Numerous meta-analyses have evaluated the therapeutic effects of probiotics on diarrhea and constipation in the pediatric population (7, 9, 16–18). However, their findings remain inconsistent (9, 19–21), likely due to differences in statistical approaches and heterogeneity in study designs. To address these discrepancies, we applied a uniform statistical methodology to synthesize the evidence and provide a more definitive assessment of the effects of probiotic supplementation on diarrhea- and constipation-related outcomes in children.

The present meta-analysis was conducted in accordance with the PRISMA guidelines (22). The protocol for this study has been documented in the International Prospective Register of Systematic Reviews (PROSPERO).

The present umbrella of systematic reviews and meta-analysis attempted to summarize the available data evaluating the effect of probiotics on diarrhea and constipation outcomes among children. Accordingly, probiotic supplementation significantly reduced the RR values for diarrhea incidence and prevention in children compared to the control group. This outcome is consistent with a Cochrane review, which concluded that probiotics are effective in preventing antibiotic-associated diarrhea (AAD) in children, with specific strains showing increased effectiveness (30). Also, probiotic supplementation was associated with a reduced odds of diarrhea incidence in children specifically. In addition, probiotics were able to shorten the duration of diarrhea in study subjects. Focusing on pediatric populations, a meta-analysis demonstrated that the duration of diarrhea in children receiving probiotics was significantly shorter than in control groups, and the length of hospital stay was also reduced (31). All these findings point to beneficial effects of probiotics as an adjunctive approach in managing diarrhea across different age groups.

The types of diarrhea included across the analyzed studies varied and encompassed AAD, infectious diarrhea, and cases where the etiology was not explicitly stated. This heterogeneity may influence the pooled estimates, as the efficacy of probiotics is known to differ depending on the underlying cause (30). For example, probiotics such as Lactobacillus rhamnosus and Saccharomyces boulardii have demonstrated greater efficacy in managing infectious and antibiotic-associated diarrhea, respectively (32). Clinicians should consider probiotic strains with well-established efficacy, such as Lactobacillus rhamnosus and Saccharomyces boulardii, administered at dosages typically ranging from 10⁹ to 10¹⁰ colony-forming units (CFU) per day, consistent with doses used in clinical trials (33, 34). Accordingly, the variability in diarrhea type should be considered when interpreting the overall results, and future meta-analyses may benefit from stratifying outcomes based on etiology to enhance clinical relevance.

Based on the available evidence, some probiotic strains were more effective in improving gastrointestinal outcomes in children. Lactobacillus rhamnosus GG and Saccharomyces boulardii were consistently associated with significant reductions in the duration and frequency of acute diarrhea, particularly in cases of viral or antibiotic-associated etiology (33, 34). These findings are supported by several high-quality randomized controlled trials with low risk of bias. In contrast, the evidence for constipation was more variable, with Bifidobacterium lactis and Lactobacillus casei rhamnosus showing moderate effectiveness in improving stool frequency and consistency (35). However, the quality of evidence for constipation-related outcomes was generally lower, often limited by small sample sizes and heterogeneous outcome measures.

Moreover, probiotics resulted in decreased stool frequency in children. While, Dong et al., demonstrated improved defecation frequency following probiotic treatment in children (36). This discrepancy is justified by smaller number of included studies and lower sample size in Dong et al.’s study (36), which may affect the statistical power to detect significant changes. Also, this issue shed the light that microecological differences between children and adults may lead to variations in constipation-related outcomes.

Furthermore, odds of diarrhea incidence were significantly affected by single-strain probiotics. Whereas both single-strain and multi-strain probiotics effectively reduced diarrhea duration, as well as the risk of diarrhea incidence. It is worth noting that while single -strain probiotics demonstrated beneficial effects on diarrhea-related outcomes and stool frequency, they were also shown to increase stool consistency in constipated patients. Given this, caution is warranted in interpreting these findings. Accordingly, Schnadower et al. demonstrated that probiotics single-strain (Lactobacillus rhamnosus) was ineffective in the treatment of acute enteritis in children (37). Similarly, Szymański et al. reported no significant changes in relation to diarrhea symptoms following Lactobacillus reuteri administration (38). However, Zhang et al. highlighted that enhanced diversity of microbiota can improve constipation-related measures significantly. This underscores the effectiveness of multi-strain probiotics in addressing constipation (39). Previous studies have demonstrated strain-specific effects of probiotics in different health status (40–42). For example, in constipated children some probiotics have been known as discriminative species such as Bacteroides and Bifidobacterium longum species (43).

Probiotic administration resulted in significant improvements in reducing the duration and frequency of diarrhea in children. This effect was particularly significant in cases of acute viral diarrhea. The therapeutic efficacy of probiotics is also strain-dependent, with specific strains such as Lactobacillus rhamnosus and Saccharomyces boulardii showing the greatest benefit (44). Furthermore, while single-strain and multi-strain formulations have been used, current evidence suggests that clinical outcomes are more influenced by individual characteristics and strain viability than by the number of strains present (45). In addition, probiotic supplementation serves as an adjunct to standard diarrhea management protocols.

The relatively modest impact of probiotics on constipation observed in pediatric populations may be attributed to several factors. Constipation is a multifactorial disorder influenced by diet, hydration, physical activity, gut motility, and psychosocial elements, which probiotics alone may not fully address (35). Additionally, the heterogeneity of probiotic strains studied, differences in dosage, and variability in intervention duration complicate the interpretation of efficacy (46). The mechanisms by which probiotics might alleviate constipation—such as modulation of gut microbiota composition, enhancement of short-chain fatty acid production, and improvement of intestinal transit—may require longer treatment periods or higher doses than those employed in existing trials (47). Furthermore, outcome measures in constipation studies often vary widely, and subjective symptom reporting can affect the reliability of results. Finally, individual differences in baseline microbiota composition may influence response to probiotic supplementation, underscoring the need for personalized approaches in future research (48).

Several underlying mechanisms have been proposed through which probiotics influence gastrointestinal disorders such as diarrhea and constipation. Probiotics are known to modulate gut microbiota composition, helping to restore microbial balance. It has been shown that probiotics compete with pathogenic bacteria for adhesion sites which may affect the incidence of infectious diseases causing diarrhea and alleviating constipation (49). On the other hand, probiotics stimulate the intestinal immune cells and commensal microflora to regulate immune responses by activation of regulatory T cells (Tregs) (50, 51). Also, probiotics can improve the integrity of the intestinal barrier through strengthening tight junctions. This action prevents the adhesion of pathogenic bacteria to mucosal epithelial cells, and prevents translocation of harmful pathogens and toxins (49, 51). Moreover, probiotics were effective in alleviating inflammation state associated with diarrhea (52). It seems that each of these mechanisms may be possible through various strains. For example, Saccharomyces boulardii and lactobacilli modify immune pathways to remove the pathogens (50). Lactobacilli increases the production of immunoglobulins in the gut which contribute to production of interferons. It has been demonstrated that Lactobacillus rhamnosus GG (LGG) could produce antimicrobial substances to inhibits the growth of Escherichia coli, streptococci, and Clostridium difficile (50).

Although probiotics are generally considered safe for use in children, especially in healthy children, long-term safety data remain limited. Most clinical trials have focused on short-term administration during acute illness, and few studies have evaluated long-term or repeated use of probiotics. Rare adverse events, such as infections in immunocompromised individuals, highlight the need for cautious use in vulnerable populations (33, 34). Furthermore, the variability in probiotic formulations and lack of close regulatory oversight may lead to inconsistent safety profiles. Adherence to probiotic supplementation can also affect clinical efficacy, particularly in chronic conditions such as constipation where long-term administration may be necessary. Factors that influence adherence include: formulation palatability, dosing frequency, and caregiver education (53). Ensuring user-friendly formulations and clear instructions can improve adherence and optimize outcomes. Future research should prioritize long-term safety monitoring and explore strategies to increase adherence in pediatric populations.

As a strength, this study is a high-level research synthesis method that integrates findings from multiple meta-analyses in relation to effects of probiotics on diarrhea and constipation outcomes. So, this study provides more comprehensive overview of probiotics evidence, reliable conclusions and bias-minimized assessment. Moreover, this study included larger population to analyze the effects of probiotics in children. However, this study had some limitations too. First, several factors including: various type of preparation, purity, storing methods and cold chain principles (maintaining appropriate temperature conditions during storage and transportation to preserve the viability of live microorganisms) may result in different outcomes. Second, the number of studies on diarrhea caused by radiation, chemotherapy, HIV, and Clostridium difficile–associated diarrhea was insufficient to reach a confirm conclusion. Third, it is important to highlight changes in the intestinal flora, which were not reported in the included studies. Forth, included studies were heterogeneous in term of sex distribution.

This umbrella of meta-analysis supports the potential role of probiotics in relation to diarrhea and constipation outcome in children. Probiotic supplementation contributed to a declined risk and odds of diarrhea incidence compared to control group. Additionally, they were able to shorten the duration of diarrhea and did not increase stool frequency and consistency too. Furthermore, subgroup analysis revealed that both single and multi-strain probiotics were able to reduce the diarrhea duration and the risk of diarrhea incidence. Therefore, further investigations on special types of the probiotics, their purity, and their combination with prebiotics may be much helpful.