WebMD Ask the Pharmacist

Rapid Weight Loss

What Are the Risks of Rapid Weight Loss?

Rapid weight loss creates physical demands on the body. Possible serious risks include:

• Gallstones, which occur in 12% to 25% of people losing large amounts of weight over several months.
• Dehydration, which can be avoided by drinking plenty of fluids.
• Malnutrition, usually from not eating enough protein for weeks at a time.
• Electrolyte imbalances, which rarely can be life threatening.

Other side effects of rapid weight loss include:

• Headaches
• Irritability
• Fatigue
• Dizziness
• Constipation

The dangers of rapid weight loss increase with the time spent on the diet. Eating a no-protein diet is particularly risky.

Is Rapid Weight Loss Ever a Good Idea?

Rapid weight loss diets can have ill effects, but so does obesity. For this reason, very low calorie diets (VLCDs) are considered a reasonable weight loss option for people with obesity (having a body mass index --BMI -- greater than 30).

VLCDs are doctor-supervised diets lasting several weeks. The meals are nutritionally balanced, but expensive -- people can end up spending thousands of dollars over time. VLCDs safely produce a loss of 15% to 25% of body weight in 12 weeks. (That's for those who finish the program: 25% to half of people can't). Sustained weight loss is comparable to that of regular dieters.

Most people seeking rapid weight loss, though, usually do it on their own. Frequently, it's to achieve a short-term goal, such as fitting into a dress, or looking good at the beach.

Starving yourself is certainly not a good idea. But if you're otherwise healthy, a brief period of extreme calorie restriction isn't likely to hurt you. You should tell your doctor what you're doing, and be sure to include protein in your diet (70 to 100 grams per day). Take a multivitamin, and eat potassium-rich foods (tomatoes, oranges, and bananas).

Also, remember that crash diets rarely help you achieve a sustained, healthy weight. Most people put the pounds right back on.