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 cell poison that has been implicated in ulcerative colitis. Sulfide generation in the colon is probably driven by dietary components such as sulfur-containing amino acids (SAAs) and inorganic sulfur (eg, sulfite).


OBJECTIVE
We assessed the contribution of SAAs from meat to sulfide production by intestinal bacteria with use of both a model culture system in vitro and an in vivo human feeding study.


METHODS
Five healthy men were housed in a metabolic suite and fed a sequence 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 were measured in samples collected on days 9 and 10 of each diet period. Additionally, 5 or 10 g bovine serum albumin or casein/L was added to batch cultures inoculated with feces from 4 healthy volunteers. Concentrations of sulfide, 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 diet and were significantly related to meat intake (P: < 0.001). Sulfide formation in fecal batch cultures supplemented with both bovine serum albumin and casein correlated with protein digestion, as measured by the disappearance of Lowry-reactive substances and the appearance of ammonia.


CONCLUSIONS
Dietary protein from meat is an important substrate for sulfide generation by bacteria in the human large intestine.
Magee
E A
EA
Dunn Clinical Nutrition Centre, Hills Road, Cambridge, United Kingdom. e.magee@dundee.ac.uk
Richardson
C J
CJ
Hughes
R
R
Cummings
J H
JH
D000328:Adult; D000603:Amino Acids, Sulfur / Q000378:metabolism*; D018592:Cross-Over Studies; D004032:Diet; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism*; D005243:Feces / Q000737:chemistry; D006801:Humans; D007420:Intestine, Large / Q000378:metabolism* / Q000382:microbiology; D008297:Male; D008460:Meat; D008875:Middle Aged; D012044:Regression Analysis; D013431:Sulfates / Q000652:urine; D013440:Sulfides / Q000302:isolation & purification / Q000378:metabolism*
D000603:Amino Acids, Sulfur; D004044:Dietary Proteins; D013431:Sulfates; D013440:Sulfides