How Weight Gain and Weight Loss Affect Your Period

A sudden change may affect your menstrual cycle

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Gaining weight or losing weight can have an impact on your menstrual cycle—either positive or negative. For example, a weight change might take you from irregular to regular, or it might make your periods come less frequently or stop altogether. It depends not just on how much you gain or lose, but where you started from.

Typically, periods last for seven days and start 28 days apart. If you're overweight or underweight, your periods are more likely to be irregular.

A woman's feet are on a bathroom scale and one foot is covering the weight reading.

Rick Elkins / Getty Images

Weight Gain

Rather than looking at just the number on your scale, it's important to know your body mass index (BMI). BMI is a way to gauge how much body fat you have. To determine your BMI:

  1. Weigh yourself

  2. Measure your height in inches, then square it (multiply it by itself)

  3. Divide your weight by your height squared

  4. Multiply by 703

So if you weigh 150 and you're 65 inches tall, the formula would look like [150/(65)2] x 703 = 24.96. That number then determines whether your weight is considered normal/healthy as opposed to underweight, overweight, or obese.

Category  BMI
Underweight Below 18.5
Normal weight 18.5-24.9
Overweight 25-29.9
Obese 30 and up
Source: Centers for Disease Control and Prevention

If you have a body mass index (BMI) that's considered normal and you gain weight, it's possible that you may skip your period. Increasing your body's fat stores (also known as adipose tissue) leads to a hormonal imbalance that can stop your ovulation.

There's no defined amount of weight gain that results in a missed period, but the more significant the gain and the faster it happens, the more likely it is to affect your period.

Both weight gain and weight loss can cause you to skip your period and can help regulate your period.

Your menstrual cycle is a result of a complex interaction between your ovaries and your brain. Changes in your hormone levels cause ovulation, and more hormonal changes result in your period. Anything that interferes with this interaction can stop your body from ovulating. If you don't ovulate, you'll skip a period. 

What happens to your period when you have a significant fluctuation in your weight depends on what weight you are starting from. For example, if you are starting at a normal weight, gaining or losing weight may cause you to skip your period.

While, if you are underweight or very overweight and not menstruating, gaining weight or losing weight will likely restart your regular period. 

Woman using a hot-water bottle on her belly to relieve abdominal pain
 VOISIN / Getty Images

The greater your BMI (typically in the obesity range over 35), the more likely you are to miss your period. It is even possible to stop bleeding altogether, a condition known as secondary amenorrhea.

It is also possible that you may have irregular noncyclic bleeding or abnormal uterine bleeding. Usually, when you are very overweight this irregular bleeding can be very heavy.

Gaining Weight When Underweight

If you are underweight it is likely that you may not be getting your period. Typically calorie restriction, excessive exercise, or illness are behind your low BMI. These are stressors on your body that cause hormonal changes that interfere with ovulation. This also causes a very low estrogen level, which is especially bad for your bone health.

When you gain weight from a low BMI, you are reducing the stress on your body. This allows your body to ovulate again, and as a result, menstruate. It also restores your body's estrogen production and protects your bones.​​

Losing Weight From a Normal Weight

Just like weight gain, there is no defined amount of weight loss that results in missed periods when starting from a normal weight. The more weight you lose and the faster you lose it, the more likely your period will be affected.

Sudden and significant calorie restriction paired with strenuous exercise may cause a stress response that alters your hormone levels, interrupts ovulation, and causes you to miss your period. This results in a lower estrogen level in your body, which is especially harmful to your bone health.

Losing Weight When Overweight

If you are significantly overweight, especially if your BMI is over 35, it is likely that you are not getting your periods regularly. Your increased fat mass or adipose tissue produces extra estrogen that is partly responsible for problems with your ovulation and missed periods.

The excess estrogen associated with obesity can increase your risk of breast and uterine cancer. Losing weight will restore your regular periods and correct your estrogen excess.

Having regular periods is a good indicator of relative hormonal balance in your body. Both the extremes of being very underweight or very overweight result in hormonal imbalances that stop your periods and over time can lead to serious health issues.

You can correct the hormonal imbalances by either gaining or by losing weight to achieve a healthy BMI. This should restart your ovulation and your periods.

A Word From Verywell

If you are starting on a plan to gain or lose weight it is a good idea to meet with your healthcare provider, a nutritionist, and maybe a personal trainer. Your goal should be to lose fat not lean body mass if you are overweight and to gain lean body mass, not just fat if you are underweight.

Make lifestyle changes that will last the rest of your life, and set goals that realistic and achievable. Maintaining your body weight within the normal BMI range (18.5 to 24.9) is one of the most important steps in achieving good overall health.

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7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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