I found this article at Yahoo. It worries me. Does anyone know more about this?

Low-Carb Diets Tax Kidneys, May Weaken Bones
Tue Aug 13, 2:36 PM ET

NEW YORK (Reuters Health) - Diets that are heavy on protein-rich foods and skimp on carbohydrates can increase the risk of kidney stones and reduce the body's ability to absorb calcium after just 6 weeks, researchers report.

Their findings come at a time when an increasing number of Americans, seduced by anecdotal accounts of fast weight loss, are turning to low-carbohydrate, high-protein (LCHP) diets. With an estimated 50% of American adults either overweight or obese, many are looking for a surefire way to shed pounds.

But while LCHP diets have been shown to get the pounds off in the near term, these diets are less successful over the long run and may even be hazardous to health, researchers warn.

For one, protein-rich foods can be high in fat, which increases the risk of heart disease and type 2 diabetes. A dearth of carbohydrate-rich foods such as fruits and vegetables can leave the body hungry for essential vitamins and minerals, while insufficient glucose (sugar) from carbohydrates, the body's preferred fuel source, can lead to fatigue and dizziness.

And according to the new study, 6 weeks on an LCHP diet increased the acid load to the kidneys, raising the risk of kidney stones. Animal protein has been shown to boost urinary excretion of oxalate, a compound that combines with calcium and other compounds to form the deposits commonly known as kidney stones.

At the same time, adults in the study had higher levels of calcium in their urine, suggesting a decreased absorption of the bone-building mineral and an increased risk of osteoporosis, according to the report in the August issue of the American Journal of Kidney Diseases.

"Consumption of an LCHP diet for 6 weeks delivers a marked acid load to the kidney, increases the risk for stone formation, decreases estimated calcium balance, and may increase the risk for bone loss," write Dr. Shalini T. Reddy from the University of Chicago, Illinois, and colleagues.

Their study included 10 healthy adults aged 21 to 52 who consumed their usual diet for 2 weeks, followed an LCHP diet for 2 weeks, and then followed a diet that restricted carbohydrates only moderately for 4 weeks. The protein-restricted diets included 3 liters of fluid a day.

Study volunteers lost an average of 9 pounds, but most developed ketones--compounds that are formed when the body uses its own fat as fuel and can raise acid levels in the blood. Acid excretion, a marker of acid levels in the blood, rose by 90% in some volunteers but none of the dieters developed metabolic acidosis, a potentially life-threatening condition caused by excessive breakdown of fats, the report notes.

There was also a sharp rise in urinary calcium levels during the LCHP and maintenance diets despite only a slight decrease in calcium intake. Urinary citrate, a compound that inhibits kidney stone formation, decreased.

While it is not clear from the study whether bone mass was affected, the findings indicate that such diets may increase the risk of bone loss over the long term.

"We already know that osteoporosis is going to be a major issue as the population ages, and if people are going to eat this kind of diet on a long-term basis, it's unknown what the implications would be for your bones," Dr. Chia-Ying Wang, a study author, said in a prepared statement.

SOURCE: American Journal of Kidney Diseases 2002;40:265-274.