The relationships between the meal energy density and postprandial gastric emptying, intestinal propulsion and absorption, and pancreaticobiliary secretions were investigated. Nine different 300-ml liquid test meals with energy densities ranging from 2.5 to 7.2 MJ l-1 were studied by means of a multiple-indicator dilution technique. The higher the energy density of the meal, the slower the gastric emptying of the test meal marker (P < 0.01). Despite slowing of gastric emptying of the meal marker the higher the energy density of the meal, the more energy was emptied to the duodenum during the 1st h after meal intake (P < 0.01). The small-intestinal transit time for the mid-portion of the meal correlated positively with energy density of the test meal (P < 0.05). Despite the prolonged time for transit through the jejunal test segment after meals with high energy density, the fractional absorption of energy varied only 50-70%, with no correlation to the energy density of the meal. As a consequence, more energy passed unabsorbed from the test segment to lower parts of the intestine after meals with high energy density (P < 0.05). We conclude that the energy density of a liquid meal is a strong determinant for the subsequent gastrointestinal adaptation. This relates not only to gastric emptying but also to intestinal transit and absorption of nutrients. The early onset of regulation suggests a role for the gastrointestinal tract in modulating the availability of systemic energy, which might be of importance for short-term regulation of food intake.