Low intakes of dietary fiber and magnesium are associated with insulin resistance and hyperandrogenism in polycystic ovary syndrome Original paper

What was studied?

This study evaluated dietary and lifestyle contributors to insulin resistance (IR) and hyperandrogenism in women with polycystic ovary syndrome (PCOS), specifically focusing on fiber and magnesium intake. Conducted as an observational cohort study at a reproductive medicine center in Canada, researchers enrolled 87 women with PCOS and 50 subfertile women without PCOS. The study aimed to determine if differences in caloric intake or physical activity could explain obesity and metabolic abnormalities in PCOS, and whether specific dietary patterns or micronutrients were associated with PCOS phenotypes and IR.

Who was studied?

The participants included 87 women diagnosed with PCOS based on Rotterdam criteria and 50 control women without PCOS, all aged between 20 and 44. Among the PCOS group, some were classified as having hyperandrogenic PCOS (HA-PCOS) and rest as non-hyperandrogenic. The study population was ethnically diverse, comprising East Asian, European, South Asian, Aboriginal, and South American backgrounds. Participants completed 3-day dietary and activity logs, wore pedometers, and underwent hormonal and metabolic testing, including HOMA-IR calculations for insulin resistance.

What were the most important findings?

The most striking discovery was that women with PCOS, despite having higher BMI and waist-hip ratios, did not consume more calories nor engage in less physical activity than the control group. Instead, they consumed significantly less dietary fiber and magnesium. Within the PCOS group, those with IR had lower fiber and magnesium intakes and a higher glycemic load. Fiber intake was negatively correlated with several metabolic and hormonal markers, including HOMA-IR, fasting insulin, 2-hour glucose, triglycerides, testosterone, and DHEAS levels, while positively correlated with HDL cholesterol. Similarly, magnesium intake was inversely related to IR, C-reactive protein, and testosterone levels, and positively associated with HDL cholesterol.

Fiber and BMI together accounted for 54% of the variance in HOMA-IR, marking fiber intake as a major microbial-modifiable dietary factor. These associations are particularly relevant in the microbiome context since dietary fiber significantly impacts gut microbial composition, increasing short-chain fatty acid (SCFA)-producing bacteria like Faecalibacterium prausnitzii and Roseburia spp., which in turn can enhance insulin sensitivity and modulate systemic inflammation.

What are the greatest implications of this study?

This study challenges the assumption that obesity in PCOS is primarily due to overnutrition or inactivity and instead points clinicians toward specific nutritional targets, fiber and magnesium, as modifiable factors linked to metabolic dysfunction and androgen excess. The clinical implications are significant: increasing fiber and magnesium intake could become a frontline, non-pharmacological strategy in managing IR and hyperandrogenism in PCOS. Moreover, as fiber-rich diets influence microbiome diversity and function, these findings offer a mechanistic basis for future interventions targeting the gut microbiome in PCOS management. Integrating dietary fiber and magnesium monitoring into clinical assessments could better personalize nutrition-based care strategies for women with PCOS.