If you've put on a surprising amount of weight in a short time, water retention, or oedema, may be the cause. You may wake up some morning to find that you have suddently gained several pounds overnight. Oedema---a common and usually harmless condition---can occur for various reasons. It is different from actual weight gain, but it can be hard to discern water weight from fat.
Weigh yourself in the morning, two or three days in a row. If you gain a pound or more in 24 hours, it's probably water weight. In fact, according to the American Heart Association, it takes an extra 3,500 calories to put on a pound of actual fat! That means an active 30-year-old woman would have to eat 5,900 calories to put on a pound of fat in one day---more than double her recommended intake of 2,400 calories.
Track your eating habits. Sodium intake and dehydration are common causes of water retention. The American Dietetic Association recommends that the average adult drink at least eight cups of water a day, more if you exercise regularly. So although it may feel like the last thing you want to do, cut back on high-sodium foods and soft drinks, drink more water, and see if you notice a change. Drinking more water will actually help your body release the fluids your cells are holding on to.
Ask your doctor whether any medications you are taking may cause water retention. According to the Mayo Clinic, some common medications, such as NSAIDs -- like ibuprofen and aspirin -- diabetes and blood pressure medications, and birth control pills have been linked to oedema.
Look at the calendar, if you're a woman. Researchers at the McKinley Health Center point out that rapid water weight gain, especially in the abdomen and breasts, is a common symptom of premenstrual syndrome (PMS). It can also be a symptom of pregnancy. If you're pregnant or think you may be pregnant, speak with your doctor right away to make sure your oedema is within normal limits.
Check for swelling in your hands, feet, and ankles. The American Academy of Family Physicians cautions that if your rings are suddenly too tight, your shoes feel too small for your feet, or your skin looks swollen and shiny, there's a good chance you're suffering from oedema rather than simple weight gain, which tends not to accumulate in those areas.
Oedema is usually harmless, but it can be a sign of an underlying health condition. If your oedema is severe, very uncomfortable, or lasts more than a few days, contact your health care professional.