RESUMEN
BACKGROUND: The primary objective was to determine whether consumption of conjugated linoleic acids (CLAs) affected the fecal microbiota composition, fecal enzyme activity or fecal composition. METHODS: Human subjects consumed (1 L/day) cows' milk (4% fat) containing (5 mg/g fat) cis-9, trans-11 CLA (CONT), (32 mg/g fat) cis-9, trans-11 CLA (NAT) and (32 mg/g fat) trans-10, cis-12 CLA and cis-9, trans-11 CLA (SYN) for 8 weeks, in addition to their normal diet. Milk feeding periods were separated by 4 week washout periods. Fecal samples were obtained at the beginning (day 0) and the end (day 56) of each milk feeding period. Fecal samples were analysed for microbiological profile, enzyme activity, pH and short chain fatty acid content. RESULTS: Samples taken at day 0 and day 56 indicated that the numbers of lactobacilli and bifidobacteria significantly decreased after consumption of all experimental milks; total aerobes, total anaerobes, enterobacteria, and enterococci + streptococci did not change. At day 56, the activities of beta-glucosidase, nitroreductase, and urease enzymes had decreased compared to samples taken on day 0 for all treatments. beta-glucuronidase activity did not change. Fecal pH and ammonia content did not change. CONCLUSION: It was concluded that observed changes could have been attributed to increased milk intake; no differences could be attributed to consumption of the different CLAs.