How does the menstrual cycle affect blood sugar levels?
Hormonal fluctuations of estrogen and progesterone during the menstrual cycle have an impact on glucose metabolism and insulin sensitivity.
The menstrual cycle is separated into the follicular phase (pre-ovulation) and the luteal phase (post-ovulation). The follicular phase is characterized by low progesterone and a short rise and fall of estrogen, and the luteal phase demonstrates rising estrogen and progesterone, with a drop in both before menstruation due to lack of fertilized egg.
During the menstrual cycle, the body engages in energetically intense processes like ovulation and building up the uterine lining to receive a fertilized egg. Sex hormones like estrogen and progesterone appear to play a role in energy metabolism, insulin sensitivity, and how glucose is processed in the body. In general, estrogens seem to promote insulin sensitivity, and progesterone promotes insulin resistance. (However, there is evidence that estrogen can also increase insulin resistance, specifically in pregnancy.)
Research, including some using continuous glucose monitors, has shown that glucose concentrations in the luteal phase (post-ovulation) are significantly higher than in the follicular phase. Concordantly, in some studies, there is an increase in insulin resistance in healthy women during the luteal phase of the menstrual cycle (when the progesterone-to-estrogen ratio is high) in comparison to the follicular (pre-ovulation) phase (when the estrogen-to-progesterone ratio is high). This suggests that the reduction in insulin sensitivity during the luteal phase depends on the increased level of progesterone.
Animal studies show that estradiol (estrogen) improves the expression of insulin signaling molecules in skeletal muscle. Estrogens exert beneficial metabolic effects by lowering body fat and improving insulin sensitivity in females.
In some studies, fasting insulin rises before ovulation and reaches a maximum during the luteal phase. This indicates relative insulin resistance during the luteal phase of the cycle, in agreement with studies showing lower insulin sensitivity in the luteal phase using glucose tolerance tests.
Based on this literature, given relative insulin resistance during the luteal phase (post-ovulation), it seems reasonable to focus on minimizing glucose- (and insulin-) stimulating foods during this time to minimize the glycemic impact of this phase.
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