Duration of fast alters fasting glucose levels, response to oral glucose load, and weight in the mouse

Fasting alters glucose metabolism and insulin resistance. To determine the effect of various fast durations on circulating glucose levels prior to and after an oral glucose load, C56BL/6 mice were fasted for 0, 5, 10, or 24 hours (n =3–4 per group). After a 30‐min baseline period, mice received an oral glucose load (2 g/kg, post‐fast body weight) via gavage. Blood glucose levels were measured during baseline and 15, 30, 45, 60, 75, and 90 min after oral glucose administration. Post‐fast body weight was significantly lower after a 24‐hour fast (20.6 ± 0.6 g), compared to 0, 5, or 10 hours of fasting (24.0 ± 0.5, 22.7 ± 0.6, and 23.1 ± 0.7 g, respectively; all p ≤ 0.01). Fasting blood glucose levels were not different among the 0‐, 5‐, and 10‐hour fasted groups (173 ± 8, 198 ± 2, 206 ± 10 mg/dL, respectively); however, after a 24‐hour fast, baseline levels were significantly lower (120 ± 20 mg/dL; all p < 0.01). Mean increase from baseline blood glucose levels following oral glucose administration were significantly greater in the 5‐hour fasted group (303 ± 10 mg/dL) than either the 10‐ or 24‐hour fasted animals (253 ± 14 and 254 ± 20 mg/dL, respectively; both p = 0.01). These results indicate that fast alters glycemic parameters in mice; therefore, it is not appropriate to compare metabolic finding in mice fasted for different durations. P. Schork was supported by The American Physiological Society Frontiers in Physiology Fellowship.