1. Three studies were carried out in each of six normal volunteers to investigate how lipid, when given at different stages during the course of a meal, affects gastric emptying and postprandial blood glucose and insulin concentrations.
2. The control meal consisted of 300 ml beef consommé (50 kJ, 12 kcal), followed 20 min later by 300 g mashed potato (908 kJ, 217 kcal). In the two test meals, 60 g margarine were incorporated into either the soup or the mashed potato.
3. The addition of margarine to either component of the meal delayed gastric emptying of the mashed potato (P < 0.05), but the pattern varied according to the component to which the fat was added.
4. Incorporation of fat into the soup increased the lag phase (P < 0.05) but did not influence the slope of emptying of the mashed potato, while incorporation of fat into the mashed potato reduced the slope of emptying of the mashed potato (P < 0.05) but did not influence the lag phase.
5. Addition of fat to either component of the meal reduced postprandial blood glucose (P < 0.05) and insulin responses, but when the fat was incorporated in the soup, peak glucose and insulin responses were delayed as well (P < 0.05).
6. The results show that the effect of fat on gastric emptying and absorption of nutrients depends on when, in relation to the other components of the meal, the fat is consumed.