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Thursday 28 April 2016

Effects of a 12-month Low-Carbohydrate Diet vs. a Low-Fat Diet on Bone Mineral Density: A Randomized Controlled Trial


Background Despite health benefits, diet-induced weight loss has been thought to decrease bone mineral density (BMD) and increase the risk of osteoporotic fractures. However, results from clinical trials on this topic have been variable; there is little to no evidence regarding the effect of low carbohydrate diets on BMD.
Methods We examined the effects of a low-carbohydrate diet (<40 g/day; n = 9) versus a standard low-fat diet (<30% kcal/day from total fat, <7% saturated fat; n = 12) on BMD among 21 obese women who took part in a 12-month clinical trial and were free of diabetes, cardiovascular disease or chronic renal disease at baseline. Intake of total energy or protein was not restricted. BMD was measured using dual X-ray absorptiometry at baseline and after 12 months of intervention.
Results Median (Interquartile range) age at baseline was 52.7 (10.7) years in the low-carbohydrate group and was 51.8 (11.7) years in the low-fat group. Nineteen participants (90%; 8 white and 11 black) completed the intervention. On average, participants in the low-carbohydrate group lost 2.1 (4.0) kg while those in the low-fat group lost 0.2 (6.7) kg at 12 months. Baseline level of physical activity and change in physical activity at 12 months did not differ between the two groups. At 12 months, participants on the low-carbohydrate diet preserved more bone mass in the femoral neck than those on the low-fat diet (Table). Preservation of total femoral and lumbar L1–4 BMD was not statistically different between groups. Similar patterns were seen for T scores and Z scores. Results were consistent after excluding two participants with a family history of osteoporosis.
Conclusion Despite greater weight loss, a low-carbohydrate diet resulted in better preservation of BMD than a standard low-fat diet among obese women.

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