What are gallstones?

Gallstones are clusters of solid material that form in the gallbladder. The most common type is made mostly of cholesterol. Gallstones may occur as one large stone or as many small ones. They vary in size and may be as large as a golf ball or as small as a grain of sand.

Experts estimate that 10 to 15 percent of people in the United States have gallstones - as many as 42 million Americans. Most people with gallstones do not know that they have them and experience no symptoms. Painless gallstones are called silent gallstones. Sometimes gallstones can cause abdominal or back pain. These are called symptomatic gallstones. In rare cases, gallstones can cause serious health problems. Symptomatic gallstones result in about 800,000 hospitalizations and more than 500,000 operations each year in the United States.

What are gallstones?

Gallstones develop in the gallbladder, a small pear-shaped organ located beneath the liver on the right side of the abdomen. The gallbladder is about 3 inches long and 1 inch wide at its thickest part. It stores and releases bile into the intestine to help digestion.

Bile is a liquid made by the liver. It contains water, cholesterol, bile salts, fats, proteins, and bilirubin (a bile pigment). During digestion, the gallbladder contracts to release bile into the intestine, where the bile salts help to break down fat. Bile also dissolves excess cholesterol.

According to researchers, cholesterol gallstones may form in several ways, such as:

• When bile contains more cholesterol than it can dissolve.
• When there is too much bilirubin or other substance in the bile that causes cholesterol to form hard crystals.
• When there are not enough bile salts to break down fat.
• When the gallbladder does not contract and empty its bile regularly.

What are the symptoms of gallstones?

Some common symptoms of gallstones or gallstone attack include:

• Severe pain in the upper abdomen that starts suddenly and lasts from 30 minutes to many hours.
• Pain under the right shoulder or in the right shoulder blade.
• Nausea or vomiting.
• Indigestion after eating high-fat foods, such as fried foods or desserts
.

Is obesity a risk factor for gallstones?

Obesity is a strong risk factor for gallstones, especially among women. People who are obese are more likely to have gallstones than people who are at a healthy weight. Obesity in adults can be defined using the body mass index (BMI), a tool that measures weight in relation to height. The table below shows how the BMI calculation works. A BMI of 18.5 to 24.9 refers to a healthy weight, a BMI of 25 to 29.9 refers to overweight, and a BMI of 30 or higher refers to obesity.

As BMI increases, the risk for developing gallstones also rises. Studies have shown that risk may triple in women who have a BMI greater than 32 compared to those with a BMI of 24 to 25. The risk may be seven times higher in women with a BMI above 45 than in those with a BMI below 24.

Researchers have found that people who are obese may produce high levels of cholesterol. This leads to the production of bile containing more cholesterol than it can dissolve. When this happens, gallstones can form. People who are obese may also have large gallbladders that do not empty normally or completely. Some studies have shown that men and women who carry fat around their midsections may be at a greater risk for developing gallstones than those who carry fat around their hips and thighs.

Is weight-loss dieting a risk factor for gallstones?

Weight-loss dieting increases the risk of developing gallstones. People who lose a large amount of weight quickly are at greater risk than those who lose weight more slowly. Rapid weight loss may also cause silent gallstones to become symptomatic. Studies have shown that people who lose more than 3 lbs per week may have a greater risk of developing gallstones than those who lose weight at slower rates.

A very low-calorie diet (VLCD) allows a person who is obese to quickly lose a large amount of weight. VLCDs usually provide about 800 calories per day in food or liquid form, and are followed for 12 to 16 weeks under the supervision of a health care professional. Studies have shown that 10 to 25 percent of people on a VLCD developed gallstones. These gallstones were usually silent - they did not produce any symptoms. About one-third of the dieters who developed gallstones, however, did have symptoms and some of these required gallbladder surgery.

Experts believe weight-loss 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. Following a diet too low in fat or going for long periods without eating (skipping breakfast, for example), a common practice among dieters, may also decrease gallbladder contractions. If the gallbladder does not contract often enough to empty out the bile, gallstones may form.

Tags: Diets and Weight Loss

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.