Dieting and Gallstones

Illustration of a gallbladder with gallstones
PIXOLOGICSTUDIO/SCIENCE PHOTO LIBRARY / Getty Images

As most people know, there are significant health benefits to be gained from losing excess pounds. For example, many people can reduce high blood pressure and cholesterol levels through weight loss. Overweight people are at greater risk of developing gallstones than people of average weight. However, people who are considering a diet program requiring very low intake of calories each day should be aware that during rapid or substantial weight loss, a person's risk of developing gallstones is increased.

What Are Gallstones?

Gallstones are clumps of solid material that form in the gallbladder. They may occur as a single, large stone or many small ones. Gallstones are a mixture of compounds, but typically they are mostly cholesterol.

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.

Causes

Gallstones develop in the gallbladder, a pear-shaped organ beneath the liver on the right side of the abdomen. It's about 3 inches long and an inch wide at its thickest part.

The gallbladder stores and releases bile into the intestine to aid digestion.

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.

Obese People Are More Likely to Develop Gallstones

Obesity is a strong risk factor for gallstones.

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.

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.

Losing Weight and Gallstone Risk

People who lose a lot of weight rapidly are at greater risk for developing gallstones. Gallstones are one of the most medically important complications of voluntary weight loss. The relationship of dieting to gallstones has only recently received attention.

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.

Why Losing Weight Causes Gallstones

Researchers believe dieting may cause a shift in the balance of bile salts and cholesterol in the gallbladder. The cholesterol level is increased and the amount of bile salts is decreased. Going for long periods without eating (skipping breakfast, for example), a common practice among dieters, also may decrease gallbladder contractions. If the gallbladder does not contract often enough to empty out the bile, gallstones may form.

Differences in Weight Loss Methods and Risk Levels

If substantial or rapid weight loss increases the risk of developing gallstones, more gradual weight loss would seem to lessen the risk of getting gallstones. However, studies are needed to test this theory.

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.

Weight Loss Surgery and Risk

Gallstones are common among obese patients who lose weight rapidly after gastric bypass surgery. (In gastric bypass surgery, the size of the stomach is reduced, preventing the person from overeating.)

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.

Should People Who Already Have Gallstones Try To Lose Weight?

Scientists know that weight loss increases the risk of gallstone formation. However, they don't know whether weight loss increases the risk of silent gallstones becoming symptomatic gallstones or of other complications developing. In addition to painful gallstone attacks, complications include inflammation of the gallbladder, liver, or pancreas. These are usually caused by a gallstone getting lodged in a bile duct.

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.

Treatment for Gallstones

Silent gallstones are usually left alone and occasionally disappear on their own. Usually, only patients with symptomatic gallstones are treated.

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.

Are the Benefits of Weight Loss Greater Than the Risk of Getting Gallstones?

There's no question that obesity poses serious health risks. Obesity has been linked to heart disease, stroke, high blood pressure, high cholesterol levels, and diabetes. Obesity has also been associated with higher rates of certain types of cancer, such as gallbladder, colon, prostate, breast, cervical, and ovarian cancers.

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.

Adapted from the NIDDK Weight-control Information Network

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