People who go on an extremely low calorie diet are more likely to develop gallstones than people on a moderately low calorie diet, according to a new study.
Dr. Michael Jensen, a professor of medicine at the Mayo Clinic, said dieters typically end up with similar weight loss in the long run whether they use extreme calorie restriction or more moderately restricted diets.
"You're going to end up in the same place (weight-wise), so why take the risk of ending up in the hospital with a gall bladder problem just to lose weight faster?" said Jensen, who was not part of the study.
Gallstones affect as many as 20 million people in the U.S.
Dr. Kari Johansson, the lead author of the study and a researcher at the Karolinska Institute in Sweden, said quick weight loss from very low calorie diets is thought to impact the salt and cholesterol contents of bile and the emptying of the gallbladder, both of which can contribute to gallstones.
To see how these diets affect gallstone risk in a real-world setting, Johansson and her colleagues collected information on customers' progress from a weight loss company in Sweden called Intrim.
Some of the study authors have worked for the company or serve on its scientific advisory board.
Their study included 6,640 dieters, half of whom went on a crash diet and the other half of whom went on a low calorie diet.
The crash diet involved liquid meals of just 500 calories a day for six to 10 weeks, followed by the gradual introduction of normal food, and then nine months of a weight maintenance regime of exercise and healthy eating.
The other dieters ate 1,200 to 1,500 calories a day, including two liquid meals, for three months, followed by the nine month weight maintenance period.
Health coaches at Intrim collected weight and body size information, which the researchers linked to a national health database that has records on gallstone treatments.
After three months in the weight loss program, the crash dieters lost about 30 pounds, compared to roughly 17 pounds lost among people on the low calorie diet.
One year out from the start of the diet, the extremely low calorie group had lost an average of 24.5 pounds, while the other group lost about 18 pounds.
Among those on the crash diet, 48 people developed gallstones requiring hospital treatment, and 16 people in the other group developed gallstones, Johansson and her colleagues report in the International Journal of Obesity.
They could not determine why gallstones were more common among people in the extremely low calorie group.
"One contributing factor was that they lost more weight during follow-up... another may be that they may have had a lower fat intake," Johansson said in an email to Reuters Health.
Jensen said people should have doctors supervise their health when going on a very low calorie diet, something that is recommended in the U.S.
"They should be informed about the risk/benefit tradeoff compared to using the less intensive, but also less effective, (low calorie diet) alternative," Johansson said.
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