Written by Alexa Heathorn, MS, CNS, Science Writer. Twice-daily supplementation with a multi-strain Lactobacillus and Bifidobacterium probiotic for 12 weeks significantly reduced IBS symptom severity, increased fecal short-chain fatty acids, improved intestinal barrier integrity, and lowered inflammatory markers in adults across multiple IBS subtypes.

Irritable Bowel Syndrome (IBS) is a common functional gastrointestinal disorder affecting approximately 11% of the global population¹. It is characterized by recurrent abdominal pain, bloating, gas, and irregular bowel habits, including diarrhea, constipation, or a combination of both². Although the exact cause of IBS remains incompletely understood, evidence suggests that gut microbiota imbalance (dysbiosis), impaired intestinal barrier function, and chronic low-grade inflammation may play central roles in its development. IBS is further classified into subtypes based on predominant stool patterns, including IBS with diarrhea (IBS-D), constipation (IBS-C), mixed type (IBS-M), and unclassified presentations³.

Previous research has largely focused on short-term probiotic interventions targeting isolated symptoms rather than evaluating long-term outcomes across multiple IBS subtypes and broader markers². This gap in comprehensive data has limited the clinical application of many previous findings. To address these limitations, a recent double-blind, randomized controlled trial was conducted to evaluate the effects of short-chain fatty acid–producing probiotic metabolites on symptom relief and intestinal barrier function in individuals with IBS².

Short-chain fatty acids (SCFAs) are bioactive compounds produced by specific gut bacteria in the large intestine through the fermentation of dietary fiber⁴. The primary SCFAs including acetate, propionate, and butyrate, serve as key energy sources for intestinal cells, support the integrity of the gut lining, regulate immune function, and help reduce and prevent inflammatory signaling within the gut². Through these mechanisms, SCFAs are thought to play an important role in maintaining gastrointestinal homeostasis.

Although numerous studies have demonstrated the protective and anti-inflammatory effects of SCFAs, it remains unclear whether increasing SCFA availability, particularly through targeted probiotic supplementation, can meaningfully improve symptoms across multiple IBS subtypes².

The study included 120 adults aged 18–65 years who had been diagnosed with IBS and experienced symptoms for at least six months. All participants were instructed to follow a low-FODMAP diet, record dietary intake, and engage in at least three sessions of moderate-intensity aerobic exercise per week to help standardize lifestyle factors.

Participants were randomly assigned to receive either a probiotic supplement containing 1 × 10¹⁰ CFU of Lactobacillus and Bifidobacterium strains or an identical placebo. The supplement was taken twice daily for 12 weeks.

Assessments were conducted at baseline, weeks 4, 8, and 12, and again four weeks after the intervention concluded. Outcome measures included fecal short-chain fatty acid concentrations, protein markers of intestinal barrier function including occludin, claudin-1, and zonulin, and serum inflammatory and immune markers, including C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α).

The results were as follows after 12 weeks of intervention:

Symptom Improvement (IBS-SSS):

• Symptoms improved significantly more in the probiotic group than placebo (F = 9.314, P < 0.001).
• Differences became clear by week 8 (P = 0.007) and were stronger at week 12 (P = 0.001).
• Benefits were seen across all IBS subtypes (P < 0.05).

Short-Chain Fatty Acids (SCFAs):

• Levels of acetate, propionate, and butyrate increased significantly in the probiotic group (all P < 0.01).
• These increases were strongly linked to symptom improvement (r = 0.43, P = 0.002).

Gut Barrier Function:

• Intestinal permeability improved by weeks 8 and 12 (P < 0.001).
• Protective gut lining proteins increased, particularly by week 12 (P ≤ 0.003).

Inflammation:

• Markers of inflammation (CRP, IL-6, TNF-α, calprotectin) were significantly lower in the probiotic group by week 12 (all P ≤ 0.001).

Safety:

• No significant differences in side effects or adherence between groups (P > 0.05).

Potential limitations of the study include:

• The trial was conducted at a single center, which may limit how widely the results apply to different populations or regions.
• The intervention lasted 12 weeks, any longer-term durability of symptom relief and gut barrier improvements remains unknown.
• Advanced microbiome sequencing and metabolomics testing were not performed, meaning deeper changes in gut bacterial composition and metabolic pathways were not fully explored.
• All participants followed a structured low-FODMAP diet and lifestyle program, which may have contributed to symptom improvement in both groups and makes it difficult to isolate the independent effects of the probiotic intervention.

This study demonstrates that targeted probiotic supplementation, alongside structured lifestyle guidance, can significantly reduce symptom severity in individuals with IBS. Improvements were observed across multiple IBS subtypes and were accompanied by increases in short-chain fatty acids, enhanced gut barrier integrity, and reductions in inflammatory markers. These findings support the growing understanding that restoring microbial balance and strengthening the intestinal lining may play a meaningful role in symptom relief.

While longer-term research is needed, this trial provides strong clinical evidence that probiotics designed to enhance short-chain fatty acid production may offer a safe and effective adjunct strategy for managing IBS symptoms and supporting overall gut health.

Source: Li, Erfeng, Jie Wang, Bin Guo, and Wenbin Zhang. “Effects of short-chain fatty acid-producing probiotic metabolites on symptom relief and intestinal barrier function in patients with irritable bowel syndrome: a double-blind, randomized controlled trial.” Frontiers in Cellular and Infection Microbiology 15 (2025): 1616066.

© 2025 Li, Wang, Guo and Zhang

Click here to read the full text study.

Posted February 18, 2026.

Alexa Heathorn, MS, CNS-c, is a clinical nutritionist specializing in metabolic health, hormonal balance, and gastrointestinal restoration through root-cause functional nutrition. She earned her master’s degree in Nutrition from Bastyr University and is currently a Certified Nutrition Specialist (CNS) candidate. Alexa also works as a research writer and functional health consultant, translating complex science into actionable strategies for practitioners and wellness companies. Learn more at www.bloomedwellness.com.

References:

1. Canavan C, West J, Card T. The epidemiology of irritable bowel syndrome. Clinical epidemiology. 2014;6:71–80. doi:10.2147/clep.s40245
2. Li E, Wang J, Guo B, Zhang W. Effects of short-chain fatty acid-producing probiotic metabolites on symptom relief and intestinal barrier function in patients with irritable bowel syndrome: a double-blind, randomized controlled trial. Front Cell Infect Microbiol. 2025;15:1616066. doi:10.3389/fcimb.2025.1616066
3. Goosenberg. RRNSSE. Irritable Bowel SyndromeRohit R. Nathani; Shreya Sodhani; Eric Goosenberg. StatPearls Publishing; 2025.
4. Ríos-Covián D, Ruas-Madiedo P, Margolles A, Gueimonde M, de Los Reyes-Gavilán CG, Salazar N. Intestinal Short Chain Fatty Acids and their Link with Diet and Human Health. Front Microbiol. 2016;7:185. doi:10.3389/fmicb.2016.00185