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Maggie E. Hostetter, Hannah E. Cabre, Amanda N. Gordon, Lacey M. Gould, Sam R. Moore, Noah D. Patterson, Abbie E. Smith-Ryan, FACSM. UNC Chapel Hill, Chapel Hill, NC.

BACKGROUND: Evidence suggests a lower carbohydrate to protein (CHO:PRO) ratio may positively influence metabolism in women. The purpose of this study was to evaluate the effect of CHO:PRO on metabolic flexibility across the stages of menopause. METHODS: 72 healthy females (Age=48.3±7.2 yrs; Wt=69.2±14.2 kg) were separated into 3 subgroups pre-menopause (PRE; n=24), peri-menopause (PERI; n=24), and post-menopause (POST; n=24). Respiratory exchange ratio (RER) was measured via indirect calorimetry to determine the rate of fat oxidation (FATox), carbohydrate oxidation (CHOox), and metabolic flexibility (MF) during exercise. MF was measured during submaximal exercise on a cycle ergometer with watts (W) increasing by 25 W every 2-minutes until the participants reached 75% of their heart rate reserve (HRR). The ranges of intensity excluding the warm-up phase included: ≤30% HRR (low intensity [LOW]), 31-≤50% HRR (moderate intensity [MOD]), and 51-75% HRR (high intensity [HIGH]). Overall MF was determined by the change in RER by subtracting RERREST from mean RER for each intensity (ΔRERLOW, ΔRERMOD, and ΔRERHIGH). CHO:PRO was determined from Diet History Questionnaire (DHQIII) and stratified in tertiles as >3.3g, 2.5-3.3g, <2.5g. Repeated measures ANCOVAs, covarying for estrogen and total calorie intake, were used to evaluate the group-by-CHO:PRO ratio interaction effects. RESULTS: There was no significant group by CHO:PRO interaction for ΔRERLOW (p=0.509), ΔRERMOD (p=0.890), or ΔRERHIGH (p=0.197), and no main effects for CHO:PRO ratio for MF (p=0.263-0.895). For ΔRERMOD, there appeared to be a greater decrease in MF from PRE to PERI (Mean difference (MD) ± Standard Error (SE)= 0.009± 0.031 a.u.) with little difference from PERI to POST (MD ± SE: -0.003± 0.031 a.u.). There was also no significant effect of CHO:PRO on FATox (p=0.739) or CHOox (p=0.722). CONCLUSIONS: Alterations in CHO and PRO, after controlling for calorie intake and estrogen, do not appear to influence MF as women transition to menopause. Metabolic flexibility may be blunted in both peri- and post-menopause during moderate intensity exercise. Future research is needed to understand and identify potential strategies related to diet and exercise that may help maintain metabolic flexibility for women during this transitional time.

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