The effect of nutrients on small intestinal motility is controversial. Our aim was to analyze the effect of intraduodenal infusion of mixtures of nutrients of increasing caloric load, on intestinal motility. Studies were performed in dogs with a duodenal cannula. Isosmolar infusions of saline, 0.5, 2, and 4 kcal/min were performed and motility recorded by means of infused catheters. Nonstatistically significant differences were observed between frequency of contractions during infusion of 0.5 (4.1 +/- 1.6 cpm) and 2 kcal/min (5.3 +/- 1.5 cpm) compared to control (4.3 +/- 1.9 cpm). With 4 kcal/min a significant decrease of frequency (2.7 +/- 0.9 cpm) was observed. A similar finding was observed for amplitude of contrations. With 0.5 kcal/min fasting cyclic activity was still present, but the numbers of phase III were significantly reduced, associated with an increased duration of phase II. With higher caloric loads cyclic fasting activity was replaced by marked variations of frequency, following a cyclic pattern. A lower threshold for mechanisms switching the fasting to fed state was observed, compared to those controlling frequency and amplitude.