Contribution of dietary protein to sulfide production in the large intestine: an in vitro and a controlled feeding study in humans

Background: Hydrogen sulfide is a luminally acting, bacterially derived cel l poison that has been implicated in ulcerative colitis. Sulfide generation in the colon is probably driven by dietary components such as sulfur-conta ining amino acids (SAAs) and inorganic sulfur (eg, sulfite). Objective: We assessed the contribution of SAAs from meat to sulfide produc tion by intestinal bacteria with use of both a model culture system in vitr o and an in vivo human feeding study. Design: Five healthy men were housed in a metabolic suite and fed a sequenc e of 5 diets for 10 d each. Meat intake ranged from 0 g/d with a vegetarian diet to 600 g/d with a high-meat diet. Fecal sulfide and urinary sulfate w ere measured in samples collected on days 9 and 10 of each diet period. Add itionally, 5 or 10 g bovine serum albumin or casein/L was added to batch cu ltures inoculated with feces from 4 healthy volunteers. Concentrations of s ulfide, ammonia, and Lowry-reactive substances were measured over 48 h. Results: Mean (+/- SEM) fecal sulfide concentrations ranged from 0.22 +/- 0 .02 mmol/kg with the 0-g/d diet to 3.38 +/- 0.31 mmol/kg with the 600-g/d d iet and were significantly related to meat intake (P < 0.001). Sulfide form ation in fecal batch cultures supplemented with both bovine serum albumin a nd casein correlated with protein digestion, as measured by the disappearan ce of Lowry-reactive substances and the appearance of ammonia. Conclusion: Dietary protein from meat is an important substrate for sulfide generation by bacteria in the human large intestine.