That feeling when your clothes feel a little snug around the waistline, so you check your calendar and—surprise!—your period is due in a few days. Cramps and bloating accompanied by mood swings, fatigue, and appetite changes are common symptoms and universally dreaded by anyone with a menstrual cycle.

Weight gain during periods is normal, and most of the time, it isn't the kind of weight that stays on your body. Instead, it's usually a combination of water retention and hormonal fluctuations contributing to feeling bloated and puffy, but that doesn't make it any less uncomfortable.

Let's take a closer look at why this happens and how you can minimize the effect of period weight gain.

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Is Gaining Weight During Your Period Normal?

Gaining weight during your period is normal. Although women and midwives have known and experienced it for centuries, the scientific community became interested in understanding the weight fluctuations associated with the menstrual cycle in the early 1900s, calling it "menstrual edema" (edema is the medical term for swelling from fluid).  

Body weight doesn't just shift during your period, it can change throughout the month and even the day based on factors like sleep, exercise, stress levels, and diet. Period weight gain may show up as extra pounds on the scale, or it may feel like your clothes fit differently than the day before. It's not fun but also not unusual.

How Much Weight Do You Gain During Your Period?

There isn't a lot of research on the amount of weight women gain during their period, but two to five pounds is the average. Everyone is different, but weight gain above five pounds may mean checking in with your doctor is a good idea.

What Are the Top Causes of Period Weight Gain?

Reasons for weight during your period can vary, but hormonal shifts throughout the month are usually the underlying cause.

Hormones follow a general pattern each month, rising and falling to trigger processes like ovulation (when an egg is released for fertilization) and a menstrual period when fertilization doesn't occur. Hormones also affect mood, appetite, energy levels, and so much more; it's no wonder they also influence weight.

Most of the top causes of period weight gain are associated with hormonal changes. Let's take a closer look at each.

Hormonal Changes

Estrogen and progesterone are sex hormones that may influence weight gain during your period. In a typical cycle, estrogen, the hormone responsible for regulating the menstrual cycle (among many other jobs), peaks twice: once before ovulation and again before your period starts.

Meanwhile, progesterone levels stay relatively consistent until it rises and peaks during the second half of your cycle. Both estrogen and progesterone drop dramatically at the end of the cycle, which triggers your period.

Sensitivity to the rise and fall of progesterone and estrogen is hypothesized to be the cause of PMS symptoms like bloating and water retention.³  While it may feel like you've gained weight, it's likely just excess fluid that normalizes once hormone levels rise again.

Food Cravings or Overeating

We may joke about chocolate cravings and menstruation, but there's some science behind it. Serotonin, a neurotransmitter responsible for regulating mood and appetite, decreases when estrogen levels drop. This drop can increase cravings for carbohydrates, which may boost serotonin production. Our bodies may instinctively crave carbs to increase serotonin levels and improve mood. 

Progesterone also can increase your appetite in the days leading up to your period, which explains why some people tend to crave things more right before than actually during menstruation.  In reality, it's unlikely that you will eat enough to gain five pounds, but you may retain extra water weight or just feel uncomfortable after eating extra sweets or salty foods.

Bloating and Constipation

Gastrointestinal (GI) symptoms like bloating and constipation are also incredibly common. While they don't cause direct weight gain, they can make you feel heavy and uncomfortable.

Once again, changes in progesterone may be the culprit, as the hormone can slow down gastric transit time, making it harder to have a bowel movement in the days leading up to your period. Constipation can add to bloating and cause gas and abdominal discomfort. Once menstruation begins, the opposite may be true, as inflammatory prostaglandins can lead to increased uterine contractions that cause cramps and more frequent bowel movements.

Low Magnesium

Magnesium is a mineral that helps to regulate water balance in the body and is essential for proper muscle function and bone health. It also plays a role in blood sugar balance, which helps to stabilize hunger levels and food cravings. 

Low magnesium levels may contribute to low energy, muscle cramps, mood swings, and water retention. Some research suggests that low magnesium levels can contribute to PMS symptoms, including bloating and water retention.

Skipping the Gym

Skipping a workout here and there isn't a big deal, and sometimes it's better to take a rest day when you're feeling run down. But if you aren't moving your body for a week, it may make you feel even worse. Throwing on your spandex may not feel like the most appealing thing in the world when you're on your period, but physical activity can help relieve symptoms associated with PMS.

Fluid Retention

Once again, you can thank hormones for your period water weight.³ Progesterone can affect the balance of other hormones involved in fluid regulation, such as aldosterone and vasopressin. These hormones influence sodium and water reabsorption in the kidneys, potentially leading to fluid retention.