Higher whole-body and exogenous postprandial glucose oxidation in the luteal versus follicular phase in healthy females.

Menstrual cycle phase can influence indices of carbohydrate metabolism at rest and during exercise; however, limited research has explored whether there are menstrual phase-specific differences in substrate metabolism in response to oral feeding. Using a within-subjects crossover design, 15 eumenorrheic females completed a metabolic trial in the follicular phase (FP; day 7 ± 2) and the luteal phase (LP; day 22 ± 3; 8 ± 2 days post-ovulation) of a single menstrual cycle. Following an overnight fast, participants consumed a 75 g glucose beverage enriched with a [U-13C6] D-glucose tracer. Capillary glucose concentrations, exogenous glucose oxidation, expired carbon dioxide percentage (L%CO2), and whole-body carbohydrate and fat oxidation rates were measured fasted and across 3-h postprandially. Peak 3-h glucose concentration was higher in LP versus FP (p = 0.04), with no differences in 3-h mean glucose or incremental area under the curve between phases (p = 0.34-0.63). Whole-body (p = 0.03) and exogenous carbohydrate oxidation (p = 0.002) were higher in LP versus FP. %LCO2 was elevated above fasting at all postprandial timepoints (p < 0.001) with no differences between phases (p = 0.84). In conclusion, following an oral glucose load, peak blood glucose concentration and carbohydrate oxidation rates were elevated in LP versus FP. These findings suggest postprandial substrate utilization differs by menstrual cycle phase in healthy females.