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Health Information
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Wednesday, May 14, 2008
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Dieting And Gallstones
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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 that 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.
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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.
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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.
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Yes. 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.
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Yes. 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.
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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.
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Possibly. 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.
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You bet. 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.
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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.
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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.
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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.
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Clayman CB, ed. The American
Medical Association Encyclopedia of Medicine. New
York: Random House. 1989. This authoritative reference guide
for patients has entries on the gallbladder, gallstones,
and the biliary system. It is widely available in libraries
and bookstores.
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 formation rates in patients on very-low-calorie
diets, including the role that fasting and diet composition
may play.
Yang H., et. al. Risk Factors for Gallstone Formation
during Rapid Loss of Weight. Digestive Diseases and Sciences.
Vol. 37, No. 6 (June 1992), pp 912-18. This article, written
for physicians, discusses gallstone formation in patients
on very-low-calorie diets.
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Weight-control Information Network
1 Win Way
Bethesda, MD 20892-3665
Phone: (301) 984-7378 or 1-800-WIN-8098
Fax: (301) 984-7196
E-mail: win@info.niddk.nih.gov
The Weight-control Information Network (WIN) is a service
of the National Institute of Diabetes and Digestive and
Kidney Diseases (NIDDK), part of the National Institutes
of Health, under the U.S. Public Health Service. Authorized
by Congress (Public Law 103-43), WIN assembles and disseminates
to health professionals and the public information on
weight control, obesity, and nutritional disorders. WIN
responds to requests for information; develops, reviews,
and distributes publications; and develops communications
strategies to encourage individuals to achieve and maintain
a healthy weight.
Publications produced by the clearinghouse are reviewed
carefully for scientific accuracy, content, and readability.
This e-text is not copyrighted. The clearinghouse encourages
users of this e-pub to duplicate and distribute as many
copies as desired.
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NIH Publication No. 94-3677
November 1993
e-text posted: 20 February 1998
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