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The link between PCOS and insulin resistance

Top things to know:

  • The majority of people with polycystic ovary syndrome (PCOS) have insulin resistance or high insulin
  • High insulin is both a symptom of PCOS and an underlying physiological driver
  • Testing for insulin resistance can be helpful to rule out other conditions that are commonly misdiagnosed as PCOS

Polycystic ovary syndrome (PCOS) sounds like it’s exclusively a disease of the ovaries, but it’s not. While PCOS does affect the ovaries and ovulation, it’s actually a full-body endocrine and metabolic disorder that is closely tied to insulin resistance.

What is insulin resistance?

Under normal conditions, the hormone insulin rises briefly after eating. It stimulates the liver and muscles to take up sugar from the blood and convert it to energy. That then causes blood sugar to fall, and then insulin to fall. With normal insulin sensitivity, both sugar and insulin are normal on a fasting blood test.

With insulin resistance, blood sugar may be normal, but insulin is high. Why? Because the pancreas has to make more and more insulin to try to get its message through. Too much insulin generates inflammation and causes weight gain. It can also lead to Type 2 diabetes and heart disease. Too much insulin is also an underlying physiological driver of PCOS (1).

The relationship between insulin resistance and PCOS

Insulin resistance is a key feature of both obese and lean PCOS. It occurs in 70-95% of people with obese PCOS and 30-75% of people with lean PCOS (2,3).

High insulin is not just a symptom of PCOS—it is also a major driver of the condition (1,4,5,6). High insulin can impair ovulation and cause the ovaries to make excess testosterone (7,8).

One research study observed that an increasing rate of PCOS correlates with an increase in obesity and weight gain over the last ten years (9). Another paper described a “galloping increase [of PCOS] in parallel with the rising prevalence of type 2 diabetes” (10).

Testing for insulin resistance

As a clinician who prescribes diet and natural treatments for PCOS, I find it’s essential to confirm insulin resistance with a blood test such as fasting insulin, HOMA-IR index, or a 2-hour insulin glucose challenge test.

By testing for insulin resistance, I can identify PCOS patients who do not have an insulin problem, such as the small group who have adrenal PCOS (11) and the fairly large group who have hypothalamic amenorrhea but have been misdiagnosed as “lean PCOS.”

Conventional treatment of insulin resistance and PCOS

Conventional treatment recommendations for the insulin resistance aspect of PCOS include weight loss, aerobic exercise, and the diabetic drug metformin, which improves insulin sensitivity (3). Resistance training may also be effective, but more research is needed (12).

Oral contraceptives are the other officially-recommended treatment for PCOS, but they can interfere with sugar regulation and insulin resistance that underlies PCOS (13). The link between PCOS, insulin resistance, and oral contraceptive pills has been dubbed a “modern medical quandary” in need of further research (14).

The role of fructose in insulin resistance

For my patients with PCOS, I find that the most effective dietary intervention is to reduce fructose.

Fructose itself is not a problem; only a high amount can cause harm. For example, low-dose fructose from fruit does not induce insulin resistance and is instead beneficial for insulin sensitivity and health. High-dose fructose from desserts, soft drinks, and fruit juice has a very different effect. “There is a fundamental physiological difference in how smaller and larger amounts of sugar are processed in the body,” explained one researcher (15). At a high dose, fructose can overwhelm the normal processing pathways in the small intestine and is able to reach the liver, where it can generate inflammation and impair insulin sensitivity (16). More research is needed here.

Nutritional supplements for insulin resistance and PCOS

Inositol is an intracellular messenger involved in insulin signaling and can be taken as a nutritional supplement (myo-inositol and di-chiro inositol). A 2018 meta-analysis of ten randomized trials found that inositol significantly improves markers of insulin resistance and “appears to regulate menstrual cycles, improve ovulation and induce metabolic changes in polycystic ovary syndrome” (17). The dose used in most of the randomized trials ranged from 1.2 to 4 grams per day.

Magnesium is my second favorite supplement for insulin resistance because it works to correct the widespread subclinical magnesium deficiency that some researchers suspect may be contributing to insulin resistance (18) and heart disease (19). Magnesium deficiency affects at least one-third of individuals, and probably more, and cannot be easily or reliably diagnosed by a blood test (19,20).

A recent meta-analysis concluded that magnesium supplementation is effective for treating insulin resistance in people with magnesium deficiency (21) and one small study found that co-supplementation of magnesium, zinc, calcium and vitamin D improved the insulin metabolism of PCOS patients (22).

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Lara Briden is a naturopathic doctor with 20 years of experience in women’s health. Her book is the Period Repair Manual—soon to be available in German as well as English. Follow her on Twitter and Instagram.

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