While we often think about fasting as a way to improve insulin sensitivity and manage PCOS, simply shifting the distribution of your caloric intake may yield benefits. For many women, the idea of fasting can be daunting and/or create feelings of restriction that may cause undo anxiety (this is the case for me!). So, I love that there is an easier way to achieve the hormonal benefits of fasting! The study that follows also considered lean women with PCOS, a subset of PCOS patients who are often ignored in the literature and who rarely receive nutrition or lifestyle counseling for the management of their PCOS. Finally, there’s something out there tested specifically on us!

study design

This study recruited 60 women, ages 25 to 39, with BMIs less than 23.7 who had previously been diagnosed with PCOS (Jakubowicz et al. 2013). Women who were taking any exogenous reproductive hormones (like birth control pills), insulin-sensitizing medications, or steroid medications were excluded.

The majority of the women were sedentary and were asked to maintain their status quo level of exercise throughout the intervention.

All women consumed diets consisting of 1800 calories per day, which was determined to be an amount of calories that should maintain body weight. Mealtime windows were as follows:

• Breakfast: 6AM - 9AM

• Lunch: 12PM - 3PM

• Dinner: 6PM - 9PM

The participants were given meal plans that used the following macronutrient quantities:

• Carbohydrates: 124g

• Protein: 191g

• Fat: 62g

However, consumption differed based on the timing of calories consumed. Half of the women were assigned to the “breakfast diet” with calories as follows:

• Breakfast: 980 calories (54%)

• Lunch: 640 calories (35%)

• Dinner: 190 calories (11%)

The “dinner diet” reversed these amounts:

• Breakfast: 190 calories (11%)

• Lunch: 640 calories (35%)

• Dinner: 980 calories (54%)

The women followed these diets for 12 weeks. A participant was considered non-compliant if they consumed more than 1980 calories (exceeding the target by more than 10%). Those participants who were non-compliant for more than three days in any given week were removed from the study. Two women were removed from each group for non-compliance. Additionally, two women dropped out from the breakfast diet group while three dropped out of the dinner diet group.

results - body weight/bmi

Given that the diet was not designed for weight loss, it is unsurprising that neither group experienced changes in BMI, waist-to-hip ratio, or body fat percentage.

results - insulin resistance

Among the breakfast diet participants, average fasting glucose decreased by 8%, and average fasting insulin decreased by 53%. Measures of insulin resistance, HOMA-IR and HOMA-B, decreased by 56% and 35% respectively, while a measure of insulin sensitivity, ISI, increased by 135%. These are substantial improvements in the participants’ blood sugar management! The dinner diet experienced no statistically significant changes in any of these measurements. These impacts are substantially larger than those found for time-restricted eating, although this study was also longer than the time-restricted eating study, which may explain the different magnitudes of findings.

results - sex hormones

Among breakfast diet participants, there was sex hormone binding globulin doubled on average, while free testosterone decreased by 50%, DHEA-S decreased by 35%, total testosterone by 47%, and free androgen index by 78%. All these changes imply that the diet shift likely had significant effects on pesky PCOS symptoms like excessive body and facial hair growth, acne, and male-pattern baldness. The only statistically significant change experienced by the dinner diet group was a 35% increase in one of the forms of estrogen studied.

results - ovulation frequency

Many women with PCOS do not ovulate regularly. While this has implications for health on its own, it is also particularly problematic for those women with PCOS who are trying to conceive.

Ovulation rates increased across both groups, likely due to the macronutrient composition of the diet that emphasized high protein over high carbohydrates. However, the effect was more pronounced for the breakfast diet group, where 50% of this group had ovulated by the end of the study versus only 20% in the dinner group. Additionally, only women in the breakfast diet group experienced two ovulations within the 3-month study period.

why does timing matter?

As discussed in my post on fasting, melatonin can interfere with insulin sensitivity, with the degree of interference in part determined by genetics (Garaulet et al. 2020).

It can take up to five hours for your body to digest and absorb the food you’ve eaten (Tobias and Sadiq 2022), and your body starts producing melatonin when its senses the onset of darkness (Masters et al. 2014).

If the sun sets where you are around 8pm, (assuming you’re not staring at bright screens) your body will start secreting melatonin around this time. If you’ve consumed dinner at 7pm, you may have up to 4 more hours of digestion after melatonin has been released. If you consumed even moderate amounts of carbohydrates at dinner, your body may have a hard time regulating your blood sugar due to the circulating melatonin, which will cause your pancreas to secrete high levels of insulin in its attempt to bring your blood sugar back down. This will exacerbate any existing insulin resistance that you have.

When I’ve consumed carbohydrates closer to bedtime, I’ve observed my blood sugar spiking higher overnight than the same food would have done if consumed earlier in the day. And when these spikes have occurred, my blood sugar has remained dysregulated, with peaks and dips occurring for hours. Shifting most of my caloric consumption earlier in the day would reduce the impacts of melatonin-induced insulin resistance.

discussion and future research

While the way of eating may have large health benefits for women with PCOS, implementing this diet in reality might be challenging. Dinners are often our most social meal of the day and for many families, dinnertime might be the only time the whole family is together on any given day. I would love to see a study that uses slightly less extreme shifts towards the morning, perhaps reserving 20 - 25% of calories for dinner such that family or social dinners are not entirely impossible.

It would also have been helpful for the authors to report impacts based on the level of compliance to see if those who perhaps had a larger dinner once or twice a week still experienced substantial benefit. I suspect this would be the case, but without data, we can’t know for sure.

Take-home points

Shifting caloric intake earlier in the day can improve insulin sensitivity and hormone levels for lean women with PCOS.

Implementation of this strategy may be challenging for those who tend to gather with others at dinnertime. Future work is needed to determine the level of compliance at which benefits diminish.

References

Garaulet M, Qian J, Florez JC, Arendt J, Saxena R, Scheer FAJL. 2020. Melatonin effects on glucose metabolism: Time to unlock the controversy. Trends Endocrinol Metab, 31(3): 192–204. doi: https://doi.org/10.1016/j.tem.2019.11.011

Jakubowicz D, Barnea M, Wainstein J, and Froy O. 2013. Effects of caloric intake timing on insulin resistance and hyperandrogenism in lean women with polycystic ovary syndrome. Clinical Science, 125:423–432 doi: 10.1042/CS20130071

Masters A, Pandi-Perumal SR, Seixas A, Girardin J, and McFarlane SI. 2014. Melatonin, the Hormone of Darkness: From Sleep Promotion to Ebola Treatment. Brain Disorders & Therapy, 4(1):1000151. doi: 10.4172/2168-975X.1000151

Tobias A and Sadiq NM. 2022. Physiology, Gastrointestinal Nervous Control. StatPearls Available: https://www.ncbi.nlm.nih.gov/books/NBK545268/

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.