Blood Sugar Levels Shift During Your Menstrual Cycle. Here's How To Keep Things In Check

Functional Medicine Doctor By Casey Means, M.D.
Functional Medicine Doctor
Casey Means, M.D. is a Stanford-trained physician, Chief Medical Officer and Co-founder of metabolic health company Levels.
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The menstrual cycle is characterized by changes in hormones—primarily estrogen and progesterone—that affect several processes in the body, including how we handle blood sugar, or glucose.

Studies show that glucose control changes throughout the menstrual cycle, significantly enough that we may want to pay attention to what we eat during each phase to avoid major blood sugar spikes and crashes. In addition, some evidence suggests there may be a relationship between glucose and premenstrual syndrome, or PMS.

Here's a breakdown of what's happening through different phases of the month and what practical effect it may have for you.

Why glucose levels matter.

Glucose is one of the two primary energy sources for our body, along with fat. Most of the glucose we use comes from foods we eat, primarily carbohydrates. Our body releases insulin to help shuttle glucose into our cells for energy or to storage for later use to keep our blood sugar at a base level. If we take in too much glucose—say, from carb-heavy or sugary foods—it can lead to a spike in blood sugar and a corresponding flood of insulin. 

Paradoxically, in the short term, these spikes can lead to a blood sugar crash as all that insulin drops our glucose levels. We can feel that drop as fatigue, brain fog, anxiety, or irritability. Long-term, repeated spikes or elevated glucose can cause insulin resistance, as our cells become numb to insulin's effects, and the body produces more insulin to overcome this.

Insulin resistance is perhaps the most common health concern in the U.S. and can factor in nearly all chronic conditions, including fertility challenges, heart disease, diabetes, and Alzheimer's disease. Insulin also blocks our body's ability to burn fat for energy and can increase the risk of obesity. In addition, insulin can stimulate the ovaries to make more testosterone, which can cause menstrual irregularity, as seen in polycystic ovarian syndrome.

Chronically high glucose can cause other problems as well, including inflammation and oxidative stress (an overabundance of damaging free radicals in the body). 

In short, for optimal health, we want to make diet and lifestyle choices that support stable glucose levels. Being aware of what's happening in our body, as it affects glucose and insulin control, can help. 

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The effect of menstrual cycle phases on glucose control.

For many women, the menstrual cycle lasts between 25 and 31 days. Throughout the cycle, hormones fluctuate via communication between the brain, ovaries, and uterus. The main hormones that play a role in this process are estrogen (estradiol), progesterone, luteinizing hormone, and follicle-stimulating hormone. Since the concentration of all of these hormones varies throughout the menstrual cycle, we talk about two main phases: the follicular and the luteal, separated by ovulation.

In general, we have greater hormone levels during the luteal phase—with progesterone higher than estrogen—as the body prepares to nourish a fertilized egg. Hormone levels drop if there's no fertilization, leading to the follicular phase, but estrogen tends to be higher than progesterone.

That differing ratio of hormones at each phase seems to influence our glucose control, as the body tries to conserve glucose for the parts of the process that are more energy-demanding, like ovulation and building up the uterine lining.

Research shows that glucose tends to be higher during the luteal phase post-ovulation. The higher levels of progesterone (compared to estrogen) reduce insulin sensitivity, which means insulin isn't as efficient at clearing glucose from your system, leading to higher circulating glucose.  

By contrast, glucose levels tend to be lower during the follicular phase, when estrogen is the dominant hormone. Estrogen has several beneficial metabolic effects, including modulating body fat and improving insulin sensitivity. (Indeed, when estrogen levels drop postmenopause, we sometimes see increased insulin resistance and risk of developing type 2 diabetes.)

It's worth noting that oral contraceptives work by interfering with these normal hormone level changes and thus may affect the glucose effects. Still, research is mixed, and factors such as type (combined OCP vs. the mini pill), dose, potency, and androgenicity will influence a person's hormonal profile. 

What does this mean for you?

Knowing that your body is more insulin resistant during the luteal phase (after ovulation) suggests it's a good time to avoid carb-heavy or sugary foods and prioritize low-glycemic whole foods for optimal metabolic health.

High carb intake could cause an even bigger blood sugar spike than usual since your body's ability to clear the excess glucose from your system quickly is impaired in that part of the cycle. Those spikes can lead to crashes, leaving you feeling fatigued or less sharp.

Sleep and stress can also affect our body's ability to process glucose, so emphasize good sleep habits and stress mitigation during these parts of your cycle. Here are some additional tips for maintaining stable blood sugar levels at any time of the month. 

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