Factors influencing frequency of flatus emission by healthy subjects.

The purpose of the present study was to measure the frequency of flatus emission by 25 healthy subjects and to determine if factors commonly thought to influence flatulence actually correlate with the frequency of gas passage. Over a one-week period on their usual diet, subjects passed gas 10 +/- 1 times/day [upper limit of normal (mean + 2 SD): 20 times/day]. The addition of the nonabsorbable disaccharide lactulose (10 g/day) to the diet significantly (P < 0.01) increased flatus frequency to 19 +/- 2.4 times per day. Gender, age, and the ability of an individual's colonic flora to produce methane had no significant influence on flatus frequency either on the basal or lactulose-supplemented diets. Some subjects consistently passed gas more often than did others. These individual differences appeared to result, in part, from differences in the ability of the flora to produce gas from a given quantity of fermentable material.