TAMPA, Fla. – Contrary to findings in animals, low-carbohydrate diets do not increase bone turnover, compromise bone quality, and lead to osteoporosis, according to a new 3-month study in the journal Osteoporosis International.1

"My hypothesis prior to starting the study was that we would see increased bone turnover from this diet. That was not the case. Not only was there no apparent increase in bone turnover, but the dieters lost significantly more weight [than controls]." —J. D. Carter, MD
In the study of 30 patients, those participants who went on a strict low-carbohydrate diet lost 14 more pounds than control subjects and did not show any increase in biomarkers of bone turnover, report researchers, led by J. D. Carter, MD, a rheumatologist at the University of South Florida in Tampa. This study also found that nearly all patients on the low-carb diet were in a persistent state of ketoacidosis, but researchers did not monitor other known potential adverse sequelae of this state, including mild renal insufficiency.

"The data that led up to this study (mostly in the form of animal data and theory) would suggest that a low-carb diet would lead to increased bone turnover. This, in turn, could compromise bone quality and lead to osteoporosis," Dr. Carter said. "My hypothesis prior to starting the study was that we would see increased bone turnover from this diet. That was not the case. Not only was there no apparent increase in bone turnover, but the dieters lost significantly more weight [than controls]."

Biomarkers of bone turnover similar among groups

Fifteen patients were instructed to consume a diet of <20 g of carbohydrates per day in the first month, followed by <40 g of carbohydrates per day during the remaining 2 months of the study. Control subjects had no dietary restrictions. The study's primary endpoint was levels of urinary N-telopeptide (UNTx) at 3 months. Secondary endpoints were UNTX at 1 month, bone-specific alkaline phosphatase (BSAP) at 1 month, bone turnover ratio (BSAP/UNTx) at 1 month, and weight loss.

The low-carb diet did not increase bone turnover markers compared with controls during any period in the study. Specifically, the mean UNTx increased by 1.6 in the low-carb group and 1.9 among controls at 3 months. At 1 month, UNTx decreased by 2.2 in the diet group and 3.1 among controls, researchers report. Mean BSAP decreased by 0.53 in the low-carbohydrate group and increased by 0.34 among control subjects. Moreover, there was no change in the bone turnover ration compared with control subjects, the study showed. Bone turnover ration increased by 0.08 among dieters and by 0.05 in control subjects at 1 month.

It is possible that there is an initial increase in bone turnover that is followed by some unknown compensatory mechanism that then stabilizes bone turnover, Dr. Carter speculated. "A second possibility is that there could have been a more subtle effect on bone turnover that this study didn't capture," he said. The new study was powered to detect at least a 50% increase in UNTx at 3 months, but there may be a more modest effect, he explained.

It is difficult to know whether a longer study may have yielded a different set of results, he said. "However ... it appears that the increased bone turnover may be a short-term phenomenon, if present at all," Dr. Carter told CIAOMed. "Further, these data tend to mirror the cholesterol data with low carb diets [in that] studies have suggested an initial increase in cholesterol that is followed by a gradual decline."

Reference

  1. Carter JD, Vasey FB, Valeriano J. The effect of a low-carbohydrate die on bone turnover. Osteoporos Int. In press.