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

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 cycle1, 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 syndrome2, or PMS.

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 challenges3, heart disease, diabetes, and Alzheimer's disease4. 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). 

For many women, the menstrual cycle lasts between 25 and 31 days5. 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 luteal6, 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 higher2 during the luteal phase post-ovulation. The higher levels of progesterone (compared to estrogen) reduce insulin sensitivity7, 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 effects8, 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.)

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.