Why it happens and what you can do about it

Changing levels of the hormones that control your menstrual cycle, mainly estrogen and progesterone, affect weight. One study found that women gained a pound, on average, during their cycle, likely because of water retention (more on that below).

Some women can gain as much as five pounds, says Suzy Lipinski, MD, a board-certified obstetrician-gynecologist and the medical director at Pediatrix Medical Group in Colorado.

Below are some common causes of period-related weight gain, according to experts and research.

Increased Appetite and Cravings

Period cravings aren’t just a rom-com trope — the cliché of needing chocolate during that time of the month can be attributed to the roller coaster that progesterone and estrogen ride during your cycle. “During the luteal phase, just before menstruation, increased progesterone levels can lead to heightened appetite, often resulting in cravings for high-calorie sugary comfort foods,” says Aderet Dana Hoch, RDN, the owner of Dining With Nature in New York City. “This phase may also slightly boost metabolic rate, prompting the body to seek more energy.”

Also, estrogen and serotonin (the mood-regulating hormone) are closely related, and when estrogen levels fluctuate between the luteal phase and menstruation, serotonin can, too, which can lead you to crave sugary delights or comforting carbs in an attempt to temporarily feel better, Dr. Lipinski says.

“There is some speculation that cravings for carbohydrate-rich foods are driven by the body’s desire for tryptophan, a precursor to serotonin,” says Angel Luk, RD, the author of You Can’t Out-Train a Bad Diet. Then, serotonin levels may rise, resulting in improved mood.

Fortunately, balance is usually restored later in the cycle. “During the follicular phase leading up to ovulation, elevated estrogen levels can suppress appetite by increasing the production of leptin, the satiety hormone, and reducing ghrelin, the hunger hormone,” says Hoch.

Menstrual Water Retention

Bloating and swelling are most common right before ovulation when estrogen levels peak, says Nicole Ibarra, RD, the founder of Altitude Nutrition & Fitness in Redding, California. That’s because high estrogen signals the production of aldosterone, a hormone made in the kidneys that causes salt and fluid retention. Once again, that switch is flipped with the next phase of the cycle. “When menstruation begins, you may notice a decrease in retention and the diuretic effect of progesterone,” says Hoch. “Individual tendencies, as well as diet and lifestyle, can also influence these effects.

Skipping Workouts

It’s common to feel sluggish before or during your period, and, understandably, this can lead you to skip workouts. Low energy during menstruation is at least partially due to loss of blood, which also means loss of iron, a key building block of blood that is an essential transporter of oxygen throughout the body, says Lipinski. “Heavy flow in particular can cause low blood counts, which may leave you fatigued and short of breath,” she says.

Anyone who has iron deficiency anemia or is at higher risk for low iron, such as plant-based eaters, should consult their healthcare provider about whether an iron supplement is beneficial to offset monthly menstrual blood flow.

GI Issues

Research suggests that as many as 73 percent of people with menstrual cycles experience GI symptoms in the days leading up to their period, including constipation, bloating, diarrhea, and nausea.

The two main players in gastrointestinal period stuff are progesterone and prostaglandins. Progesterone, when at its height during ovulation, can cause constipation because it slows down digestion and can make it harder to have regular bowel movements, says Eve Lepage, RN, a fertility nurse with Clue, the period tracking app. Some people experience constipation before their period, while others may deal with it during the first few days of bleeding.”

Prostaglandins, the inflammatory chemicals produced during a period that help the uterus contract and shed its lining, can have the opposite effect. ”They cause digested food in your gastrointestinal tract to move faster than usual,” Lepage says, which explains why you may have to go more often during the first couple days of your period. Prostaglandins also cause diarrhea and cramping, Lipinski adds.

Because everybody is different, exactly when these symptoms pop up can vary from person to person. One study examined more than 33,000 menstrual cycles to explore how GI symptoms fluctuate across them.

“Findings revealed that GI issues like constipation, bloating, diarrhea, and nausea are significantly more common during the luteal phase (just before menstruation) than in the follicular phase,” says Lepage. “These symptoms were present in both individuals with and without premenstrual syndrome (PMS), but those with PMS experienced more severe GI issues.”

The study also highlighted a strong connection between mood symptoms and GI symptoms. People who reported mood disturbances — such as anxiety, irritability, or depression — were more likely to experience worsened GI symptoms, whether or not they had PMS. An association between mood and gut function was consistent across both the luteal and follicular phases.

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