Abstract:
INTRODUCTION: Despite known sex differences in glucose metabolism, current clinical diabetes guidelines make no differentiation between men and women, and understanding of the mechanisms underlying these differences is lacking. With the increasing prevalence of metabolic syndrome particularly amongst young women, investigations of sex-specific differences in glucose metabolism have become more important than ever. In particular, the widespread use of synthetic female sex hormones contained within the combined, monophasic oral contraceptive pill (OCP) highlights an important knowledge gap which needs to be addressed. OBJECTIVES: The aim of this pilot study was to assess the effects of the OCP on glycaemic regulation in healthy young women, and to explore the potential benefits of a high protein diet on glycaemic control. METHODS: Healthy young women, including OCP users (n=3) and non-OCP users (n=3) were examined across the entire menstrual cycle (28-day period), using continuous glucose monitoring (CGM). Throughout the study period, subjects alternated between periods of normal (NP; 11% of total energy) and a high (HP; 24%) dietary protein intake. Diets were isocaloric, with dietary periods lasting for an average of four days at a time. Test meal challenges were performed at regular intervals throughout the menstrual cycle to assess postprandial glucose (PPG) response to standardised meals of varying protein content, such that meal protein content matched that of the diet at the time. Additionally, 24h CGM data was collected to assess overall glycaemic variability between both menstrual cycle and dietary phase. RESULTS: Fasting glucose values were comparable between groups, although OCP users had consistently higher fasting insulin and HOMA-IR levels. No significant effect of the OCP on PPG was found. However, OCP users exhibited a tendency toward prolonged PPG response compared to non-users, particularly during the NP dietary phases. This PPG response was improved during the HP phases, for OCP users only (p=<0.0001). There was no effect of OCP use, menstrual cycle phase or diet on overall 24h glycaemic variability. CONCLUSION: Clear trends observed in this pilot study suggest a tendency for OCP users to have an altered glycaemic response. Although differences were minimal, it is the accumulated effect of these alterations that is concerning. Most women take the OCP for longer than a decade. Therefore such changes in glycaemic response may put OCP users at greater risk of the development of insulin resistance, impaired glucose tolerance and metabolic syndrome. With the vast prevalence of OCP use worldwide, coupled with the increasing rates of metabolic syndrome, these metabolic effects of OCPs deserve more attention. More research will allow better interpretation of clinical findings, greatly assisting in the tailoring of dietary recommendations to young women of child-bearing age.