Role of anaerobic bacteria in weight loss and reduced food intake after jejuno-ileal bypass in the rat.

The mechanism of weight loss after small intestinal bypass was studied in Wistar rats. Weight loss after 90 per cent bypass was twice that after equivalent small-bowel resection. This was not due to differences in absorption, as faecal fat and energy excretion were equally increased after both procedures. However, when resected rats were pair fed with bypassed animals, their weight curves were identical, suggesting that diminished food intake was responsible for the increased weight loss after bypass. Anaerobic organisms were rarely found in normal small bowel but were present in high concentrations in the bypassed segment. Metronidazole administration significantly reduced weight loss after bypass, but not after resection. Cephalexin had no effect. These results suggest that approximately half the weight loss occurring after bypass is due to shortening of small bowel. The remainder can be accounted for by reduced food intake as a result of anaerobic overgrowth of the long excluded segment of bowel.