Yogurt and fermented-then-pasteurized milk: effects of short-term and long-term ingestion on lactose absorption and mucosal lactase activity in lactase-deficient subjects.

Lactase-deficient subjects absorb lactose in yogurt more effectively than lactose in other dairy products. However, as all previous studies were performed without a double-blind design and only after a single ingestion of the test product, the mechanism of this enhanced absorption remains unclear. The aims of this double-blind study were 1) to evaluate lactose absorption after prolonged ingestion of yogurt and fermented-then-pasteurized milk (FPM) and 2) to assess the modification of the lactase activity of the duodenal mucosa. In 16 lactase-deficient subjects we confirmed that yogurt enhances lactose digestion, this beneficial effect being destroyed by pasteurization. Moreover, the long-term (8 d) ingestion of either yogurt or FPM does not modify the results of hydrogen breath tests in comparison with a 24-h ingestion. The mucosal lactase (Dahlquist method) and beta-galactosidase (ONPG method) activities were not significantly modified by yogurt or FPM ingestion. These results suggest that in lactase-deficient subjects no adaptation occurs after eating yogurt or FPM and that the increased lactose absorption in yogurt must be mainly related to an intraluminal process.