Low carb diet may not weaken bones, says study
over a three-month period, say US researchers - a result that may
prove to be only a brief glimmer for this fading star of diet fads.
Low carb diets, like the once fashionable Atkins diet, have lost popularity amongst the public with critics saying that the approach puts followers at a higher risk of clogged arteries and heart attack in the long-term.
Animal studies have also suggested that the low carb, high protein diet could adversely affect bone quality. This is because consumption of high-protein diets alter the body's acid balance which could lead to increased bone turnover (bone depletion is faster than formation).
The new study, published on-line in the journal Osteoporosis International (ISSN: 1433-2965), reports that 15 volunteers eating a low-carb diet for three months did not have higher levels of bone turnover markers than the 15 controls eating a normal diet.
"I was surprised by the results," said lead researcher John Carter from the University of South Florida College of Medicine. "Patients of 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."
The three month study used overweight volunteers, with the test group consuming a low-carb diet containing less than 20 grams of carbohydrates for one month and then less than 40 grams of carbohydrates for the remaining two months. Controls ate a normal American diet with no restrictions.
The primary end-point of the trial was the level of excretion of bone resoption of the marker, urinary N-telopeptide (UNTx), after three months, with secondary end-points of UNTx after one month, bone specific alkaline phosphate (BSAP), bone turnover ratio (BSAP/UNTx) at one month, and weight loss.
While the test group lost significantly more weight than the control group after three months (6.3 kg versus 1.05 kg), the average level of UNTx increased by 1.6 in the test volunteers, compared to 1.9 in the controls. This result, say the researchers, does not show a significant change in the bone turnover between the two groups.
A major limitation of this study is that the researchers looked for a difference in bone turnover of 50 per cent, which means that subtle changes in bone quality were not observable under the design of the study.
The researchers concluded: "The diet did not increase bone turnover markers compared with controls at any time point."
However, Dr Carter said that long-term weight management by sticking to a strict low-carbohydrate diet was not recommended, saying that diets high in fat and protein could overload the kidneys with protein, as well a clogging arteries with saturated fats and cholesterol.
Atkins Nutritionals, one of the main proponents of the low carb lifestyle, filed for bankruptcy last year. It re-emerged in January with a new mission: to promote 'tasty, portable nutrition'.
