Post-exercise Insulin Sensitivity is Not Impaired After an Overnight Lipid Infusion

Abstract

2266 An increase in plasma fatty acid availability reduces insulin sensitivity. It is unclear, however, if this inhibitory effect persists after plasma FA concentrations return to basal levels. PURPOSE: To determine whether overnight exposure to elevated plasma fatty acid concentrations after exercise alters insulin sensitivity the next morning. METHODS: Four healthy women exercised for 90 min at ∼65% VO2peak on two separate occasions. On one occasion a 20% lipid emulsion with heparin was infused (LIPID; 0.11 g fat/kg/h) from 1500h on the day of exercise until 0700h the next morning. On the other occasion, saline was infused as a control (SALINE). On both occasions subjects ingested the same meals after exercise (82% carbohydrate, 7% fat, 11% protein; 2661 ± 189 kcal/day), which was designed to maintain energy balance. Hourly blood samples were taken overnight for measurement of plasma fatty acid concentrations. At 0900h, 2 h after stopping the overnight infusion, a blood sample was obtained to measure plasma fatty acid, glucose and insulin concentrations, followed immediately by an intravenous glucose tolerance test to assess insulin sensitivity (Si and AIRG) using minimal model analysis. Indirect calorimetry was used to estimate resting and exercise energy expenditure. RESULTS: Total 24 h energy expenditure was not different in SALINE and LIPID (2424 ± 57 vs. 2309 ± 93 kcals). The lipid infusion, however, increased systemic caloric availability by 1417 ± 231 kcal and the average overnight plasma fatty acid concentration was 4-fold higher during LIPID than SALINE (0.87 ± 0.08 vs. 0.22 ± 0.03 mM, p<0.05). Two h after stopping the overnight infusions, plasma fatty acid concentrations returned to basal levels and were similar in SALINE and LIPID (0.49 ± 0.17 vs. 0.30 ± 0.17 mM), as were the plasma glucose (4.7 ± 0.1 vs. 4.9 ± 0.4 mM) and insulin concentrations (9.9 ± 2.3 vs. 12.5 ± 3.2 μU/mL). Insulin sensitivity (Si: 7.3 ± 1.9 vs. 7.8 ± 2.3 [×10-4 min−1/(μU/mL)] and the insulin response to glucose (AIRG: 602.7 ± 260.2 vs. 661.0 ± 296.8 μU/mL×10min) were also not different. CONCLUSIONS: Insulin sensitivity the morning after a single exercise session was not reduced after overnight exposure to a 4-fold increase in plasma fatty acid concentration and the delivery of ∼1400 excess calories. Funding sources: NIH – NIDDK #5P60DK-20572 and NIH #M01-RR00042