Menstrual cycle phase does not affect whole body peak fat oxidation rate during a graded exercise test

Abstract

Female sex hormones fluctuate in a predictable manner throughout the menstrual cycle in eumenorrheic women. In studies conducted in both animal and humans, estrogen and progesterone have been found to exert individual metabolic effects during both rest and exercise, suggesting that estrogen may cause an increase in fat oxidation during exercise. However, not all studies find these metabolic changes with the natural physiological variation in the sex hormones. To date, no studies have investigated whether whole body peak fat oxidation rate (PFO) and maximal fat oxidation intensity (FATmax) are affected at different time points [mid-follicular (MF), late-follicular (LF), and mid-luteal (ML)] in the menstrual cycle, where plasma estrogen and progesterone are either at their minimum or maximum. We hypothesized that an increased plasma estrogen concentration together with low progesterone concentration in LF would result in a modest but significant increase in PFO. We found no differences in body weight, body composition, or peak oxygen uptake (V̇o2peak) between any of the menstrual phases in the 19 healthy, young eumenorrheic women included in this study. PFO [MF: 0.379 (0.324–0.433) g/min; LF: 0.375 (0.329–0.421) g/min; ML: 0.382 (0.337–0.442) g/min; mean ± (95% CI)] and resting plasma free fatty acid concentrations [MF: 392 (293–492) µmol/l; LF: 477 (324–631) µmol/l; ML: 396 (285–508) µmol/L] were also similar across the menstrual cycle phases. Contrary to our hypothesis, we conclude that the naturally occurring fluctuations in the sex hormones estrogen and progesterone do not affect the whole body PFO and FATmax in young eumenorrheic women measured during a graded exercise test. NEW & NOTEWORTHY Menstrual cycle phase does not affect the peak fat oxidation rate during a graded exercise test. Natural physiological fluctuations in estrogen do not increase peak fat oxidation rate. FATmax is not influenced by menstrual cycle phase in healthy, young eumenorrheic women.

The day-to-day reliability of peak fat oxidation and FATMAX

“…2h,3h,respectively). From a practical perspective, this suggests that controlling for menstrual cycle phase may not be an important requirement in studies assessing PFO, which is in agreement with recent findings by Frandsen et al (2020). Thus, more future studies can recruit female participants without using this as justification for their exclusion.…”

Caffeine increases maximal fat oxidation during a graded exercise test: is there a diurnal variation?

“…They then rested for 5 min with free access to water before beginning a maximal graded exercise test to measure their VO 2max . This began with the same warmup protocol, followed by increments of 50 W every minute until self-reported exhaustion [29]. Indirect calorimetry data were registered using a CPX Ultima CardiO2 breath-by-breath gas analyzer (Medical Graphics Corp., St. Paul, MN, USA).…”

Peak Fat Oxidation Rate Is Closely Associated With Plasma Free Fatty Acid Concentrations in Women; Similar to Men

“…The general metabolic response to acute graded exercise is similar across sexes, with increasing fat oxidation rate from light- to moderate-intensity exercise and a decreasing fat oxidation rate from moderate to high-intensity exercise with a concomitant increase in glucose oxidation (Stisen et al, 2006 ; Vest et al, 2018 ; Frandsen et al, 2020 ). When evaluating differences in the oxidation of fat and carbohydrate during exercise between men and women, it is critical to consider a number of variables, i.e., training state, body composition, and hormonal status but also consider the day-to-day reliability in the methodology (Chrzanowski-Smith et al, 2020 ).…”