Gastrointestinal function in obesity: motility, secretion, and absorption following a liquid test meal

Digestive responses to a 300-mL liquid fat-rich meal (432 kcal) in a group of massively obese patients were compared with those observed in a group of healthy lean subjects of variable body weight. Gastric and intestinal propulsion, digestive secretions, and absorption in the proximal 70 cm of intestine were measured using a multiple-marker dilution method. The average gastric emptying of energy, acid, volumes, and meal marker were similar in the two groups 80 minutes after intake, justifying a comparison of intestinal processing of the meal. Compared with lean subjects, the obese subjects responded with less pancreatic secretion (P less than .05) and gallbladder emptying, but absorbed a larger proportion of the emptied energy in the test segment (P less than .01) during a similar or shorter transit time. In addition, when the entire meals were compared, the obese group generally absorbed the test meal more effectively and rapidly in the upper part of the intestine. As a consequence, the flow volumes at the exit of the test segment were lower (P less than .05), and less of the test meal was propulsed to distal parts of the intestine. In the lean subjects, the body weight or height correlated positively with the gastric emptying rate, peak gastric acid output, and pancreatic responses, and negatively with (P less than .05) the segment transit time. The taller the subject, the greater the proportion of the meal which was rapidly propulsed unabsorbed to lower parts of the intestine, indicating that a large intestinal area was exposed for rapid energy uptake. No such correlations were observed in the obese group.