• What Are Gallstones?
• What Causes Gallstones?
• Are Obese People More Likely To Develop Gallstones?
• Are People on a Diet To Lose Weight More at Risk for Developing Gallstones?
• Why Does Weight Loss Cause Gallstones?
• Are Some Weight Loss Methods Better Than Others in Preventing Gallstones?
• Are People Who Have Surgery To Lose Weight Also at Risk for Gallstones?
• Should People Who Already Have Gallstone Try To Lose Weight?
• What is the Treatment for Gallstones?
• Are the Benefits of Weight Loss Greater Than the Risk of Getting Gallstones?
• Additional Reading

One in ten Americans has gallstones. However, most people with gallstones don't know they have them and experience no symptoms. Painless gallstones are called silent gallstones. For an unfortunate minority, however, gallstones can cause painful attacks. Painful gallstones are called symptomatic gallstones, because they cause symptoms. In rare cases gallstones can cause life-threatening complications. Symptomatic gallstones result in 600,000 hospitalizations and more than 500,000 operations each year in the United States.

Bile is a fluid made by the liver that helps in digestion. Bile contains substances called bile salts that act like natural detergents to break down fats in the food we eat. As food passes from the stomach into the small intestine, the gallbladder releases bile into the bile ducts. These ducts, or tubes, run from the liver to the intestine. Bile also helps eliminate excess cholesterol from the body. The liver secretes cholesterol into the bile, which is then eliminated from the body via the digestive system.

Most researchers believe three conditions are necessary to form Most researchers believe three conditions are necessary to form gallstones. First, the bile becomes supersaturated with cholesterol, which means the bile contains more cholesterol than the bile salts can dissolve. Second, an imbalance of proteins or other substances in the bile causes the cholesterol to start to crystallize. Third, the gallbladder does not contract enough to empty its bile regularly.

Scientists often use a mathematical formula called body mass index (BMI) to define obesity. (BMI = weight in kilograms divided by height in meters squared. The accompanying table shows BMI in pounds and inches.) For example, an obese woman who is 5 ft. 4 in. tall (64 in.) and weighs 174 pounds has a BMI of 30. The more obese a person is, the greater his or her risk is of developing gallstones. Several studies have shown that women with a BMI of 30 or higher have at least double the risk of developing gallstones than women with a BMI of less than 25. (See Table 1, Body Weights in Pounds According to Height and Body Mass Index)

Why obesity is a risk factor for gallstones is unclear. But researchers believe that in obese people, the liver produces too much cholesterol. The excess cholesterol leads to supersaturation in the gallbladder.

One major study found that women who lost from 9 to 22 pounds (over a 2-year period) were 44 percent more likely to develop gallstones than women who did not lose weight. Women who lost more than 22 pounds were almost twice as likely to develop gallstones.

Other studies have shown that 10 to 25 percent of obese people develop gallstones while on a very-low-calorie diet. (Very-low-calorie diets are usually defined as diets containing 800 calories a day or less. The food is often in liquid form and taken for a prolonged period, typically 12 to 16 weeks.) The gallstones that developed in people on very-low-calorie diets were usually silent and did not produce any symptoms. However, about a third of the dieters who developed gallstones did have symptoms, and a proportion of these required gallbladder surgery.

In short, the likelihood of a person developing symptomatic gallstones during or shortly after rapid weight loss is about 4 to 6 percent. This estimate is based on reviewing just a few clinical studies, however, and is not conclusive.

Some very-low-calorie diets may not contain enough fat to cause the gallbladder to contract enough to empty its bile. A meal or snack containing approximately 10 grams (one-third of an ounce) of fat is necessary for the gallbladder to contract normally. But again, no studies have directly linked a diet's nutrient composition to the risk of gallstones.

Also, no studies have been conducted on the effects of repeated dieting on gallstone formation.

One study found that more than a third (38 percent) of patients who had gastric bypass surgery developed gallstones afterward. Gallstones are most likely to occur within the first few months after surgery.

Although excluding people with pre-existing gallstones from a weight-loss program seems prudent, there is no evidence to support this action. If people have had their gallbladders removed, there is little risk of them having gallstones or bile problems while participating in a weight-loss program.

The most common treatment for gallstones is surgery to remove the gallbladder. This operation is called a cholecystectomy. In rare cases, drugs are used to dissolve the gallstones. Other nonsurgical methods are still considered experimental.

The drug ursodeoxycholic acid prevented gallstones from forming in one clinical trial of patients on very-low-calorie diets. However, the drug is costly. Given the small proportion of patients who develop symptomatic gallstones on very-low-calorie diets, it is not known if ursodeoxycholic acid would be a cost-effective drug to recommend for all patients undergoing such diets, though people with preexisting gallstones may benefit from this drug.

Weight loss also reduces the risk of heart disease by lowering cholesterol levels. Even a modest weight loss of 10 to 20 pounds can bring positive changes. And the psychological boost from losing weight, such as improved self-image and greater social interaction, should not be ignored.

Patients who are thinking about beginning a commercial diet program to lose a significant amount of weight should talk with their doctors. A physician can evaluate a patient's medical history, individual circumstances, and the proposed weight-loss program. Doctor and patient can then discuss the potential benefits and risks of dieting, including the risks of developing gallstones.

Everhart, J.E. Contributions of Obesity and Weight-Loss to Gallstone Disease. Annals of Internal Medicine 1993, Vol. 119, pp 1029-35. This article, written for physicians, shows how obesity as well as weight loss and low calorie diets increase the risk of gallstones.

Gallstones. NIH Publication No. 93-2897. This fact sheet provides basic information about gallstones and treatment options. It is published by the National Institute of Diabetes and Digestive and Kidney Diseases and is available through the National Digestive Diseases Information Clearinghouse, Box NDDIC, 9000 Rockville Pike, Bethesda, MD 20892, Tel: 301-654-3810.

Weinsier RL, et. al. Gallstone Formation and Weight Loss. Obesity Research, 1993; 1 (1): pp 51-56. This review article, written for physicians, examines gallstone for

e-text posted: 20 February 1998