What causes rapid weight gain & bloating?

Updated April 17, 2017

If you have ever had your weight change drastically from one day to the next, you are not alone. Rapid weight gain and bloating are both possible. The good news is you will most likely lose it as quickly as you gained it. But what causes rapid weight gain and bloating in the first place?

What Constitutes Rapid Weight Gain?

Some people would consider rapid weight gain having gained three pounds in 24 hours. Others would consider it having gained five pounds in three weeks. It is important to know if you have gained pounds in fluid or fat because fluid retention may be a sign of something health-hazardous. If you have gained several pounds in two days, all of it or the bulk of that is water-weight. It will often come off easily, usually without you doing anything differently and you can relax. If you gained five pounds in three weeks, it is likely that the bulk of it is fat, not fluids.

Fluid Retention

Many women notice rapid weight gain in the days before and during their period. They can gain several pounds then and often feel bloated. This is an example of when hormones make you retain fluids. Other times hormones can result in water retention and fast weight gain is when you take oral contraceptives containing the hormone oestrogen, anti-inflammatory drugs, steroids and some antidepressants (Reference 1). Sensitivity to certain foods and kidney, lung and heart disease can also make you retain water quickly as well (Reference 2).

Benign Rapid Fat Gain

If you suddenly change your daily intake of calories to, say, doubling them for two weeks and stop all exercise, you will most likely rapidly gain fat weight. You may have noticed that you can gain several pounds during the holidays. Often, this weight will come off by itself when you return to your normal eating and exercise habits. A woman who is pregnant will usually also gain several pounds quickly, to accommodate the growing foetus in her uterus.

Potentially Dangerous Rapid Weight Gain

You will also gain weight quickly and suddenly if you have problems with your thyroid. According to the website, "Weight gain occurs owing to fat accumulation and fluid retention caused by protein deposits in the body. The symptoms of hypothyroidism are fatigue, lethargy, swelling of the face, puffy eyes, dry skin, decreased sweating, poor memory, slow speech and husky voice, weakness, intolerance to cold and headache." Thyroid issues are the most common cause for sudden weight gain (Reference 2). Another disorder is Cushing's syndrome: "In this problem, fat accumulates in the face, abdomen and upper back; while the arms and legs usually remain slender," the website states.


If you find that you have gained weight and you know that it is not because of a sudden change in your lifestyle or pregnancy, it is strongly recommended that you make an appointment with your doctor for a thorough check-up. Rapid weight gain can be as dangerous as rapid weight loss.

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About the Author

Julia Derek is a certified Manhattan-based trainer and writer. She has 14 years experience in the fitness industry. She works at Reebok Sports Club/NY or through her company Her writing has appeared in New York Post, Los Angeles Daily News, and AM/NY. She attended George Mason University.