Background/Objective: Lifestyle intervention is recommended as first-line treatment for polycystic ovary syndrome (PCOS). This pilot study aimed to determine if a short-term hypocaloric dietary intervention induced changes in the phenotypic presentation of PCOS. Methods: Twenty women with PCOS and overweight/obesity participated in a 3-month hypocaloric dietary intervention with a 6-month follow-up. At pre-intervention, post-intervention, and follow-up, assessments of menstrual cycle status, hyperandrogenism, and polycystic ovarian morphology were performed, and PCOS phenotype status was determined using the following scale of decreasing severity: Phenotype A (ovulatory dysfunction, hyperandrogenism, and polycystic ovaries), Phenotype B (ovulatory dysfunction and hyperandrogenism), Phenotype C (hyperandrogenism and polycystic ovaries), or Phenotype D (ovulatory dysfunction and polycystic ovaries). Results: The participants lost 8 ± 3% of their initial body weight with the intervention (p < 0.001). Eight (40%) participants experienced a favorable shift in PCOS phenotype, while the remaining 12 (60%) participants had an unfavorable shift or no change. Changes in PCOS phenotype were primarily driven by reductions in menstrual cycle length (p = 0.010) and follicle number per ovary (p = 0.017), albeit no baseline clinical variable predicted a favorable-change PCOS presentation. At the 6-month follow-up (N = 12), weight was increased (p < 0.05), and seven participants (58%) had reverted to a more severe phenotype. Conclusions: Weight loss may provide temporary improvement in the phenotypic presentation of PCOS, yet sustained lifestyle change may be required to maintain these benefits.

Background/Objectives: Lifestyle interventions are first-line treatment for women with polycystic ovary syndrome (PCOS) to improve metabolic health. Impacts on reproductive function are less clear. Previous research has been limited by inconsistencies in evaluation of ovulatory function and lack of comparisons between women with and without PCOS. Methods: The present study implemented a prospective clinical trial of 28 women (PCOS, N = 10 and Non-PCOS Control, N = 18) undergoing a 1-month baseline assessment followed by a 6-month hypocaloric dietary intervention. Results: Both groups reached clinically meaningful weight loss with the intervention (PCOS group: 6.5 ± 5.5%; Non-PCOS Control group: 10.0 ± 4.7%). Largest follicle diameter and growth rate of ovulatory dominant follicle, menstrual cycle length and luteal phase length did not change during the intervention in either group (all p > 0.05). The Non-PCOS Control group had increased mid-luteal phase progesterone levels and secretory phase maximum endometrial thickness during the intervention (all p < 0.05), whereas the PCOS group showed a reduction in follicular phase length (p < 0.05). Additionally, changes in ovulatory function and endometrial development were not associated with the rate of weight loss (all p > 0.05). Conclusions: This study demonstrates that women with PCOS are unlikely to experience changes in menstrual cyclicity and endometrial development with a short-term hypocaloric dietary intervention. The shortening of the follicular phase suggests that women with PCOS may need a longer intervention to achieve clinically meaningful improvements in ovulatory function and endometrial health.