This is the second post in a series that discusses the peer-reviewed research on the potential of popular diets to address PCOS symptoms. The first post discussed the ketogenic diet, while this post will discuss the Mediterranean diet. Additional posts cover low glycemic index diets, the bean diet, and plant-based diets.
What is the Mediterranean Diet?
The Mediterranean diet was first proposed as a possible healthy way of eating in the 1950s when researchers began to observe that life expectancies were higher in the Mediterranean region than in other developed countries. The region’s dietary patterns and lifestyle were hypothesized as the reason for this longevity. It should be noted (and if you’ve traveled to the region, you've observed) that diets actually vary tremendously across countries in the Mediterranean region.
The Mediterranean Diet is often proposed as a healthier way of eating compared to the standard American diet. A lower-carb variation of the diet may be helpful for women with PCOS.
But alas, in nutrition circles, the “Mediterranean diet” has come to imply a way of eating that emphasizes whole grains, breads, fresh fruit, non-starchy vegetables, leafy greens, beans, nuts, seeds, and potatoes. Olive oil is the primary fat source consumed, which is high in monounsaturated fatty acids. The diet includes eggs, fish, poultry, and low-fat dairy products, but only in moderation to decrease consumption of saturated fat. Similarly, wine in moderation, usually with dinner, is allowed. The diet limits sugar, processed foods, and red meat. (If you’ve ever traveled to Greece, you’ll know that limiting red meat is not a feature of their diet…). The diet has been proposed as one that can reduce chronic inflammation, oxidative stress, and overall health.
While there are several peer-reviewed journal articles discussing why the use of the Mediterranean diet might be beneficial to address PCOS symptoms, there is limited empirical research published on the actual use of the Mediterranean diet to successfully reduce PCOS symptoms.
As a fellow researcher, I know that studies that find no impact from an intervention are much less likely to be published than studies that find impacts, so I question whether the lack of publications on the topic is due to a lack of research or a lack of research that actually finds the diet to be helpful. I suspect it might be the latter.
Given the Mediterranean diet’s use of whole grains and complex carbohydrates as central features of the diet, I suspect that it is actually not that great for many women with PCOS. I know that the standard form of the diet would not be an ideal diet for me or many of the clients with whom I have worked.
However, two studies specifically consider the effect of the Mediterranean diet on females with PCOS, and one of these studies modified the Mediterranean diet to be lower in carbohydrates. I think this latter approach is potentially really helpful and would be a great alternative to those who enjoy following a Mediterranean-style diet and who also have PCOS.
low carb Mediterranean diet vs. low fat diet for PCOS
I LOVE this first study (Mei et al. 2022) that uses a randomized controlled trial to compare a low-carb variation of the Mediterranean diet with a low-fat diet. For decades, we have been bombarded with propaganda about the benefits of a low-fat diet, and I honestly think a low-fat diet is detrimental for most people because it naturally shifts our consumption over to carbohydrates. While carbohydrates are not bad in moderation, when they are the bulk of our diets, they will eventually wreak havoc on insulin sensitivity for many people, especially for those with PCOS who are already prone to insulin resistance and metabolic syndrome.
This study recruited 72 women of reproductive age with PCOS from Changhai Hospital in China. The women were between the ages of 16 and 45 with BMIs of at least 24 (overweight or obese women). The study excluded anyone with thyroid or adrenal disorders, liver or kidney disease, cardiovascular disease, or mental illness. They also excluded anyone taking hormonal medications (except for progesterone-based ones) or insulin-sensitizing medications.
Participants were then assigned to follow either the low-carb Mediterranean diet or a low-fat diet, which they followed for 12 weeks.
Those in the low-carb group consumed:
a maximum of 100g of carbohydrates per day or ≤20% of their calories from carbohydrates (note, while this is lower than the average person consumes, it is not low enough to enter ketosis)
increased protein and fat
foods that fall under a traditional Mediterranean diet including whole grains, extra virgin olive oil, vegetables, moderate amounts of lean proteins like fish, meat, and dairy, and low amounts of eggs
Those in the low-fat group consumed:
<40g of fat per day or ≤30% of their calories from fat
<10% of their calories from saturated fat (within their fat allotment as described above)
no fatty meats, butter, offal, fried foods, poultry skin, or fish roe
increased amounts of cereals, vegetables, and fruit
Total calories consumed across both groups averaged about 1345 calories per day, which was approximately the amount of calories they were consuming before the intervention.
This study did not include any exercise component or make any other lifestyle changes.
The table below summarizes the results in terms of the percent change in each measure for the low-fat group and the low-carb group after 12 weeks following their respective diets. The researchers also tested for statistically significant differences in the changes observed across groups. For almost all metrics, the low-carb group experienced a larger improvement than the low-fat group.
Results for each group after 12 weeks following their respective diets. The last column indicates which group experienced a bigger improvement. “No difference” means there was not a statistically significant difference between the changes observed across groups.
Both groups experienced decreases in body weight, body mass index (BMI), waist circumference, waist-to-hip ratio, and body fat percentage. The low-carb group experienced larger decreases for all of these metrics, suggesting that a low-carb variation of the Mediterranean diet could help women with PCOS achieve a healthy weight. Similarly, both groups experienced decreases in fasting insulin levels, and HOMA-IR, a measure of insulin resistance. Both also experienced increases in QUICKI, a measure of insulin sensitivity. For all of these measures of metabolic health, however, the low-carb diet group experienced larger improvements.
Given that insulin resistance is a driving factor for PCOS symptoms, improvements in this metric suggest that PCOS symptoms (acne, excessive body hair growth, menstrual irregularity) likely improved more among the low-carb participants than among the low-fat participants.
In terms of reproductive hormones, both groups experienced decreases in testosterone levels, likely due to the reduction in insulin levels observed. Decreasing androgen hormones like testosterone can improve symptoms of PCOS. Both groups also experienced
decreases in the ratio of luteinizing hormone (LH) and follicle-stimulating hormone (FHS), which tends to be elevated in females with PCOS. This elevated ratio can contribute to irregular periods because these two hormones regulate ovulation. The low-carb diet group again outperformed the low-fat diet group in terms of hormonal imbalances.
Additionally, while we have traditionally thought that increased consumption of animal products and dietary fat contributes to increased cholesterol levels and cardiovascular disease, this study demonstrates that a diet higher in fat and presumably animal products resulted in greater improvements in total cholesterol, LDL cholesterol, and triglycerides than the low-fat diet did.
Eat your healthy fats and animal sources of protein!
The Standard Mediterranean Diet and PCOS (And also Hashimoto’s)
This second study (Kamińska et al. 2023) is not nearly as well done as the first study, but I think it is important to include because it utilizes a standard Mediterranean diet without limitations on carbohydrate consumption, and it does not result in the same magnitude of changes as found in the low-carb version of the Mediterranean diet.
This study recruited women from the Medical University of Warsaw in Poland with BMIs in the “normal” range or less than 25. Their participants included 15 females with PCOS, 14 with Hashimoto’s (an autoimmune thyroid disorder), and 24 with neither disorder. Both Hashimoto’s and PCOS are associated with weight gain.
All participants in this study attended a 90-minute lecture on the Mediterranean diet and received 7-day menus each week and they were encouraged to undertake 2.5 to 5 hours of moderate-intensity aerobic exercise each week. The intervention lasted an average of 72 days across participants.
Participants were scored for compliance based on the following criteria:
Using olive oil as their primary cooking fat
Consuming at least 4 tbsp of olive oil per day
Consuming at least 2 servings of vegetables per day (including at least 1 serving of raw vegetables)
Consuming at least 3 servings of fruit per day
Consuming less than 1 serving of meat per day (100 - 150g of meat = 1 serving)
Consuming less than 12 g of butter, margarine, or cream per day
Consuming less than 1 sweet or carbonated beverage per day
Consuming at least 7 glasses of wine per week
Consuming at least 3 servings of legumes per week
Consuming at least 3 servings of fish per week
Consuming less than 3 servings of sweets or pastries
Consuming at least 3 servings of nuts per week
Consuming more chicken, turkey, or rabbit than veal, pork, hamburger, or sausage
Consuming at least 2 dishes seasoned with sofrito (sauce made with tomato, onion, leek, garlic and simmered in olive oil) per week
The study does not report the number of calories consumed or the percent of calories coming from carbohydrates, protein, or fat.
The table below shows the percent change in each metric for those participants with PCOS, Hashimoto’s, or neither condition.
Results after an average of 72 days following the standard Mediterranean diet. “No significant change” means that the difference observed is not statistically significantly different from zero. There were also no statistically significant differences across the three groups for any metric.
We can see that the magnitude of reductions in body weight are smaller in this study compared to the one discussed above. This could be coming from the shorter duration of the study (about 72 days vs. 84 days), although the difference in study lengths is not particularly large. It could also be coming from the fact that this intervention focused on those women with so-called normal BMIs, although the participant averages are in the upper end of this range and this study included physical activity whereas the previous study did not which should have contributed to additional weight loss.
Without doing a direct comparison of a low-carb Mediterranean diet with a standard Mediterranean diet among both normal weight and overweight people with PCOS, we cannot directly compare these studies, but I strongly suspect that carbohydrate consumption is a factor in the differences in impacts found here.
Unfortunately, this study did not measure the effects of the diet on hormone levels or other health benefits like measures of cardiovascular health or metabolic health.
Limitations
As we frequently see, studies focus on interventions among those with BMIs in the overweight or obese range, leaving those with PCOS in the normal weight range uncertain about how the intervention will impact them. Weight loss can improve hormone levels, so it is unclear if women of normal weight would experience improvements in hormone levels on the low-carb Mediterranean diet in the absence of weight loss.
The second study which considers women of normal BMI fails to measure any hormone levels or menstrual cycle length, which are critical metrics to determine the efficacy of any PCOS intervention.
The better of the two studies considers a modified low-carb Mediterranean diet. I would love to see a study that considers a control group, a low-carb Mediterranean diet group, and a standard Mediterranean diet group to see if carbohydrate consumption is driving the differences in results across the two studies considered here.
Take-home points on the use of the mediterranean diet for women with pcos
The Mediterranean diet is often proposed as a healthier alternative to the standard American diet, and for many people, it is a great alternative.
The diet emphasizes the consumption of whole grains, fruits, vegetables, legumes, nuts, seeds, potatoes, and olive oil. Moderate consumption of dairy, eggs, poultry, and fish is allowed while red meat is limited.
A low-carb version of the Mediterranean diet (≤100g carbs/day) outperforms a low-fat diet in terms of changes in body weight, body composition, most reproductive hormones, cardiovascular health, and metabolic health.
The standard Mediterranean diet leads to only small reductions in body weight and small improvements in body composition. This is likely driven by the relatively high consumption of carbohydrates consumed in the standard Mediterranean diet and the presence of insulin resistance among those with PCOS.
ABOUT THE AUTHOR
Kelly Grogan, Ph.D., NTM, is a holistic nutrition therapist who is passionate about helping females with PCOS. She currently manages her own PCOS with nutrition and lifestyle tools that she developed through extensive review of the scientific literature on PCOS interventions.
Disclaimer: This post is not intended to diagnose or treat any medical issues. It is intended for informational purposes only. I am not a medical practitioner. Always consult a trusted healthcare provider with any questions you may have about a medical condition or treatment and before starting any new health care regimen.
References
Kamińska W, Wiśniewska K, Okręglicka K, Pazura I, and Nitsch-Osuch A. 2023. Lifestyle intervention towards Mediterranean Diet, physical activity adherence and anthropometric parameters in normal weight women with Polycystic Ovary Syndrome or Hashimoto’s Thyroiditis – preliminary study. Annals of Agricultural and Environmental Medicine 30(1):111–117 https://doi.org/10.26444/aaem/159156
Mei S, Ding J, Wang K, Ni Z, and Yu J. 2022. Mediterranean Diet Combined With a Low-Carbohydrate Dietary Pattern in the Treatment of Overweight Polycystic Ovary Syndrome Patients. Frontiers in Nutrition, 9:876620 https://doi.org/10.3389/fnut.2022.876620