Date

April 2008

Document Type

Thesis

Degree Name

M.S.

Department

Dept. of Dietetics and Nutrition

Institution

Oregon Health & Science University

Abstract

Low-carbohydrate (CHO) diets are popular in the United States because of the promises of quick and easy weight loss, but the health effects of these diets on bone have yet to be described. Low-CHO diets severely restrict the amount of carbohydrate a person can eat in one day; consequently, several foods are excluded from the diet, including milk and yogurt, fruits, starchy vegetables and grains. Restricting these foods may result in low consumption of the bone-related nutrients including calcium, potassium, and magnesium. Also, restricting carbohydrate intake greatly increases protein and fat intake, a pattern that may negatively affect skeletal health. While previous studies report that low-CHO diets result in increased urinary calcium excretion, the impact of low-CHO diets on bone turnover and bone quality have not been established. We hypothesized that individuals consuming a low-CHO weight loss diet would have increased urinary calcium excretion and bone turnover, subsequently resulting in decreased bone quality compared to those consuming a high-CHO weight loss diet after six months. This prospective, parallel cohort, randomized, interventional study compared the effects of following a low-CHO or high-CHO weight loss diet on bone health after six months. Bone health was assessed in 115 overweight and obese adults by measuring calcium intake, urinary calcium excretion, bone turnover markers, and bone mineral content (BMC) and bone mineral density (BMD). Differences in absolute values at six months and changes from baseline were compared using independent sample t-tests, correlational analysis, repeated measures analysis of variance (ANOVA), multivariate and univariate linear regression models, and post-hoc analysis. Energy intake decreased in both groups (-343 ± 87 kcal/d in high-CHO vs -447 ± 107 kcal/d in low-CHO), but the differences were not significantly different between groups. Dietary intake of calcium was significantly lower at six-months in the low-CHO group compared to the high-CHO group whether reported as absolute intake (613 ± 216 mg/d vs 793 ± 522 mg/d; p<0.05) or as dietary calcium density (402 ± 164 mg/1000 kcal vs 512 ± 276 mg/1000 kcal; p<0.05). The low-CHO group lost more weight (-13 ± 0.9 kg) than the high CHO group (-8 ± 1 kg; p<0.01). The mean change from baseline in urinary calcium excretion was higher in the low-CHO group than the high-CHO group (0.099 ± 0.03 mmol/mmol creatinine vs 0.014 ± 0.23 mmol/mmol creatinine; p<0.05). The mean change in urinary calcium excretion rate was higher in the low-CHO group than the high-CHO group (46 ± 17 mg/24 hr vs -3.5 ± 11 mg/24 hr; p<0.01). There were no significant changes in bone turnover markers within or between groups. Whole body BMC increased in the low-CHO group (p<0.05); however, the changes in whole body BMC were not significantly different between groups. Spine BMC increased significantly in both groups (p<0.01 and p<0.05, respectively), but the changes were not significantly different between groups at six-months. No other significant differences or changes in bone quality were found. These results provide evidence that low-CHO diets followed to promote weight loss in an overweight and obese population increase urinary calcium excretion compared to a high-CHO diet but do not change bone turnover markers or bone quality over six months.

Identifier

doi:10.6083/M48S4MVD

School

School of Medicine

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