The effect of milk and lactobacillus feeding on human intestinal bacterial enzyme activity.

Twenty-one subjects were recruited for a study designed to investigate the effect of oral supplements of Lactobacillus acidophilus on fecal bacterial enzyme activity. Three bacterial enzymes were assayed: beta-glucuronidase, nitroreductase, and azoreductase. These fecal enzymes can catalyze procarcinogens conversion to a proximal carcinogen. The sequence of feeding studies and fecal enzyme assays was the same for all subjects: 4 wk of a control period; 4 wk of plain milk feeding; 4 wk of control, without any dietary supplements; 4 wk of milk containing 2 X 10(6) per ml viable L acidophilus; and 4 wk of control, without any supplements. The concentration of viable lactobacilli simulates that found in acidophilus supplemented milk. Reductions of 2- to 4-fold in the activities of the three fecal enzymes were observed only during the period of lactobacilli feeding. These changes were noted in all subjects and were highly significant (p less than 0.02 to 0.001). During the final control period, after lactobacilli feeding, fecal enzyme levels returned to normal after 4 wk.