Lactose is a disaccharide found in dairy products, which provide energy and essential nutrients. Digestion of lactose relies on the intestinal enzyme lactase, or lactase-phlorizin hydrolase, located on the brush border of the small bowel mucosa. This enzyme splits lactose into two absorbable monosaccharides: glucose and galactose. When lactase activity is insufficient, undigested lactose proceeds to the colon where it is fermented by the gut flora, generating gas that trigger the uncomfortable symptoms associated with lactose intolerance. Lactase non-persistence is extremely common, affecting approximately 70% of the adult population world-wide. Prevalence varies markedly across geographic regions, typically ranging from 50 to 90% in African, Asian, and South American countries. The subjective diagnosis of lactose intolerance requires the occurrence of symptoms such as abdominal pain, bloating, flatulence and diarrhea following the ingestion of high lactose dairy products. An objective assessment of lactose intolerance may be achieved with a specific breath test that measures hydrogen emission in breath following the ingestion of lactose. Consequently, current international guidelines require concurrent report of typical symptoms and pathologic breath test results in order to diagnose lactose intolerance. Management of lactose intolerance often involves dietary restrictions and the prescription of formulations that contain lactase. However, one should recognize that avoiding dairy products can increase the risk of nutritional deficiencies. Therefore, ongoing research is focused on alternative strategies, notably utilizing gut microbiota in order to improve tolerance to lactose. This review aims to explore the evidence supporting the use of probiotics as a potential treatment strategy to alleviate the symptoms of lactose intolerance by modulating colonic metabolism and enhancing lactose digestion.

Background: Bloating, gas, and abdominal discomfort are common in healthy individuals but lack effective interventions. Probiotics can alleviate some gastrointestinal (GI) symptoms; however, evidence for their impact on bloating, gas and abdominal discomfort in otherwise healthy populations remains limited. Mechanistic studies suggest that synbiotics may influence the underlying mechanisms of bloating, including increased gas production, impaired gut motility, and visceral hypersensitivity, but there is a paucity of data from large trials evaluating clinical outcomes. Accordingly, we evaluated the effects of a multi-species synbiotic on GI symptoms. Methods: In a randomized, double-blind, placebo-controlled, decentralized trial, participants (n = 350) with self-reported bloating/indigestion received either a multi-species synbiotic (53.6 billion AFU multi-species probiotic and 400 mg pomegranate extract; DS-01) or placebo daily for 6 weeks. Outcomes included GI quality-of-life (DQLQ), bloating and gas (PROMIS-GI 13a), abdominal discomfort (PROMIS-GI 5a), constipation, regularity, mood-related symptoms, and safety. Results: The multi-species synbiotic improved GI quality-of-life compared to placebo (0.80 vs. 1.20; p < 0.05) at Week 6. Bloating and gas were reduced in the synbiotic arm compared to placebo (16.0 vs. 21.0; p < 0.01), with more participants reporting never/rarely bloating (72.3% vs. 55.9%; p < 0.001). Abdominal discomfort also decreased (8.0 vs. 10.0; p < 0.01). Additionally, there was a statistically significant improvement in constipation symptoms and regularity in the synbiotic arm relative to placebo. Conclusions: Daily supplementation with this multi-species synbiotic significantly improved GI quality-of-life, bloating, gas, abdominal discomfort, and bowel habits. This is the first synbiotic to demonstrate meaningful improvements in bloating and gas in a generally healthy, diverse, real-world population.

Background The intestinal-gas symptoms of irritable bowel syndrome (IBS) are particularly bothersome and refractory. In our Japanese clinical practice, we often experience IBS patients with severe complaints of excess 'flatulence' or 'rumbling' as well as bloating, and have considerable difficulty in treating them. However, few studies have been reported on this subgroup of IBS for whom intestinal-gas symptom is the most bothersome (gas-predominant IBS). Aims The aim of this study was to characterize the features of refractory gas-predominant IBS and to find an effective treatment strategy. Methods One hundred and forty-six consecutive patients who fulfilled the Rome IV criteria for IBS were divided into subgroups according to the most distressing symptom. Among these subgroups, we focused on a gas-predominant IBS group. 'Flatulence' is defined as 'excess flatulence' or 'incontinence of flatulence'. Patients with gas-predominant IBS were treated with paroxetine, amitriptyline, or both. 'Remission-like improvement' was defined as achieving a severity rating of 30% or less for all IBS symptoms within 24 months, and no relapse occurred for at least six months. Results Of the 146 patients, 31 (21.2%) were classified ashaving gas-predominant IBS. All were refractory to conventional treatment. Ten did not meet the required treatment conditions (lack of treatment-related information (n=6) and deviation from the treatment protocol (n=4)) and were excluded, leaving the data of 21 patients available for study. Of the 21 studied patients, the most bothersome symptoms were 'flatulence' in 14 (66.7%), 'rumbling' in three (14.3%), both 'flatulence' and 'rumbling' in three (14.3%) and bloating in one (4.8%). Notably, 17 (81.0%) rated 'flatulence' and six (28.6%) rated 'rumbling' as one of the worst symptoms. Fifteen (71.4%) of the 21 patients exhibited very high anxiety scores for both state and trait anxiety, while a total of two (9.5%) were diagnosed with a psychiatric disorder, major depressive disorder. Eighteen (85.7%) of the 21 patients achieved 'remission-like improvement' with five to 23 months of treatment with paroxetine (n=14), amitriptyline (n=2), or both (n=2), and no relapse occurred for at least six months. Conclusions In Japan, there is a distinct refractory subgroup of IBS who complain of intestinal-gas symptoms such as 'flatulence' or 'rumbling' as their most distressing symptom. Further studies are needed on the prevalence and regional specificity of gas-predominant IBS in Japan and globally. Paroxetine treatment for a relatively long period may be effective in treating refractory gas-predominant IBS. However, this study was open-label and lacked a control group, and future investigations are needed to determine the most appropriate use of paroxetine for the treatment of gas-predominant IBS.