Low Carbohydrate Diet Did Not Increase Bone Loss, Study Finds

Low carbohydrate diets have become popular as a weight loss technique; however, critics contend such diets may have harmful side effects. One concern has been that low carbohydrate diets, which replace calories from carbohydrates with more consumption of high-protein foods like meat and eggs, alter the body's acid balance. This imbalance could lead to increased bone turnover (more rapid depletion than formation of bone) -- increasing the risk for osteoporosis.

"That's not what our study found," said lead author John D. Carter, assistant professor in the Division of Rheumatology, USF College of Medicine. "Patients on the low carbohydrate diet did lose weight, but the diet did not appear to compromise bone integrity or lead to bone loss."

Earlier animal studies suggested that low carbohydrate, high protein diets could adversely affect bone quality.

"I was surprised by the results," Dr. Carter said. "People on low carbohydrate diets absorb less calcium through the gut and excrete more calcium in the urine, so you'd expect they would be leaching their bones."

Dr. Carter emphasized he does not advocate strict low-carbohydrates for long-term weight management. Such diets may adversely overload the kidneys with protein and lead dieters to consume more artery-clogging saturated fats and cholesterol, he said.

The USF study followed 30 overweight patients for three months. Half followed a strict low carbohydrate diet -- consuming less than 20 grams of carbohydrates a day the first month and then less than 40 grams a day for the remaining two months. The control half ate a normal American diet with no restrictions. The researchers used blood tests to measure the patients' breakdown and formation of bone and checked urine for signs that the dieters were complying with their low-carbohydrate diets.

The difference in bone turnover between the low carbohydrate dieters and the non-dieters was insignificant after three months. But, the dieters lost significantly more weight -- an average of 14 pounds -- than the patients on unrestricted diets.

A potential limitation of the USF study was that the researchers looked for at least a 50 percent difference in bone turnover between the dieters and non-dieters. It's possible that more subtle effects on bone quality might have been found, Dr. Carter said, particularly if the low carbohydrate diet was maintained beyond three months.

The study's other authors were USF rheumatologists Frank Vasey, MD, and Joanne Valeriano, MD.