Dear Doctors: I'm pretty good about eating a healthy diet. The exception is each month during my period, when all I seem to want is potato chips and ice cream. Is there something going on with my body, or is this just a good excuse for a few cheat days each month?
Dear Reader: Eating a healthful diet means putting a daily limit on the sweet treats and salty carbs that can wreak havoc on weight management, blood pressure and blood sugar. That kind of sustained discipline makes the occasional cheat day a welcome break. But when it comes to the intense food cravings that can occur during the menstrual cycle, years of research suggest that the many changes taking place in the body during that time are a significant factor. These include rising and falling levels of estrogen, progesterone, cortisol, serotonin and insulin. Levels of ghrelin and leptin, the so-called hunger hormones, also seesaw during the menstrual cycle. Ghrelin boosts feelings of hunger, whereas leptin promotes satiety.
Now, a small study from researchers in Germany, which was published last year in the journal Nature Metabolism, suggests that brain chemistry plays a significant role in period cravings. Specifically, the cycle of hormonal shifts that take place during a woman’s menstrual cycle cause the brain to become more sensitive to changes in insulin levels. The hormone insulin, which is produced by the pancreas, regulates blood sugar. It is also able to cross the blood-brain barrier. The body’s response to insulin has an effect on hunger and cravings.
The researchers conducted two experiments. In the first, they used a device known as a glucose clamp to measure changes to insulin sensitivity in the brains of 11 young women as they went through the phases of a menstrual cycle. They found that during the follicular phase, which is when the egg is being prepared to leave the ovary, the brain becomes more sensitive to insulin. Insulin sensitivity is associated with good blood sugar control and a stable appetite. But during the luteal phase, which is when the egg travels to the uterus and waits to be fertilized, insulin sensitivity in the brain measurably decreased. That suggested that this phase of menstruation, which is when food cravings typically occur, is marked by insulin resistance. This is a metabolic state that prevents the cells from absorbing glucose from the bloodstream, which in turn can cause an increase in hunger.
In the second experiment, conducted with a different group of 15 young women, the researchers again measured changes to insulin sensitivity throughout the phases of a menstrual cycle. The women underwent MRIs, which verified the original findings.
The idea that insulin resistance in the brain can have an effect on appetite is intriguing. It not only offers an explanation for the food cravings that many women struggle with during their periods, but it also points to new avenues of research in obesity and diabetes. However, as is true of all small studies, this is just a beginning. More research is needed to confirm these findings and to further explore their effects on the body.
(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
