Dietary and Microbial Determinants of Intestinal Sulfur Gas and Malodor: Mechanisms, Phenotypes, and Nutritional Mitigation

Intestinal gas and malodor are common nutrition-related concerns that may influence dietary adherence, gastrointestinal symptoms, and quality of life. Although gas volume and odor are often treated as a single outcome, they arise from partly distinct processes. Bulk intestinal gas is generated principally through swallowed air, acid-bicarbonate reactions, and microbial fermentation, whereas malodor is determined mainly by trace volatile sulfur compounds, including hydrogen sulfide, methanethiol, and dimethyl sulfide. Their production depends on dietary sulfur amino acids, sulfate, taurine, host-derived substrates, microbial cross-feeding, intestinal transit, luminal chemistry, and gas-liquid partitioning. This review integrates evidence concerning dietary determinants of intestinal gas, gut microbial sulfur metabolism, nutritional and microbiome-directed interventions, and downstream odor-control strategies. The concept of conditional sound-odor discordance is retained as a secondary framework illustrating that gas volume, acoustic intensity, and odor burden should not be considered interchangeable endpoints. Human dietary trials indicate that low-FODMAP diets and substrate-specific enzymes may reduce fermentation-related symptoms or total gas production, but they do not necessarily suppress sulfur-derived odorants. Probiotic evidence remains strain-specific and largely indirect, whereas sulfide-binding compounds and external adsorptive devices target odor-active molecules more directly. Future nutritional studies should combine controlled dietary exposure with measurements of gas volume, volatile sulfur compounds, microbial functional pathways, intestinal transit, and perceived odor.