When PMS is about to hit, many women forego their diets and dive into the depths of junk food. We shamelessly swap our celery stick for a slice of chocolate cake, a bowl of pasta, or both, and satisfy our ravenous appetite for carbs. A study published in Annals of Endocrinology suggests food cravings before our period are triggered by fluctuating levels of hormones, including estrogen and progesterone, and may lead women to eat 500 extra calories per day.

"There are often dietary compulsions during this period of the cycle, especially for sweet foods and chocolate," wrote the researchers.

The craving for carbs is triggered by the brain, not our taste buds. For example, carb craving is a signal we need to eat something sweet or starchy, because the brain needs to make serotonin. Typically, this food craving is accompanied by a bad mood. Previous research has found when people have an urge to eat carbs, they’re usually stressed, irritable, angry, depressed, or tired, among other things. These moods are reflective of a change in neurotransmitters like serotonin.

Researchers from the National Institute of Nutrition and Food Technology in Tunisia sought to explore whether a change in diet before menstruation is linked to fluctuating serotonin levels and mood swings. A total of 30 healthy women between the ages 18 and 45 were monitored for changes in hormone levels, calorie intake, and weight.

The findings revealed between day one to three of the “follicular” phase, or menstruation, the women consumed an average of approximately 1,700 calories a day. However, in the three days leading up to menstruation, the women ate an extra 500 calories a day. More than half of the increase in calories was due to carbohydrates; the women gained 0.66 pounds more before their period than while they were ovulating.

Fluctuations in estrogen and progesterone levels are known to affect serotonin activity and levels, which play a big role in mood swings and food cravings. When serotonin levels are low during the late “luteal” phase, or right before our period, eating foods rich in sugar and carbs will lead to a spike in serotonin and dopamine levels, boosting our mood and making us feel better, according to a 2003 study in PNAS.

In a similar study carried out at the Massachusetts Institute of Technology, researchers had women with severe PMS stay at the MIT Clinical Research Center at the beginning and end of their menstrual cycle. These healthy women increased their caloric intake by more than 1,100 calories daily when they were premenstrual, and the calories came entirely from carbs. The researchers discovered low serotonin activity was behind their food cravings and premenstrual moods.

In reality, the brain wants what it wants. When the brain craves carbs to increase serotonin production, it will haunt us until we give in to carb-laden foods. We do have control of the carbs we choose to eat — healthy carbs like brown rice, multigrain bread, yogurt, and fruits, among others, is a healthy alternative.

Source: National Institute of Nutrition and Food Technology in Tunisia. Menstrual Cycle and Appetite Control. Annals of Endocrinology. 2016.