The Atkins New Diet Revolution (1), a low-carbohydrate, high-protein (LCHP) diet, has been the center of debate among health care professionals in recent years. Proponents of the diet claim that it stimulates weight loss and reduces chronic disease risk. Conversely, critics suggest that the disproportionate amount of fat negatively impacts blood lipids (cholesterol and triacylglycerols) and increases risk for cardiovascular disease. Further, the excess protein may stimulate bone loss and increase the risk for osteoporosis (2), a debilitating disease defined by reduced bone mass and breakdown of the microarchitecture of the bone (3).
In recent years, a plethora of independent research studies were conducted to determine the effectiveness of LCHP diets, modeled after the Atkins diet plan, on weight loss and risk factors for cardiovascular disease compared to traditional high-carbohydrate, low-fat (HCLF) diets. Surprisingly, after six months, these studies showed that the LCHP diet did not negatively affect blood cholesterol or triacylglycerol concentrations (4-7). Moreover, participants following the LCHP diet lost more weight and exhibited greater decreases in triacylglycerol concentrations compared to individuals consuming a traditional, HCLF diet (5-7). While these initial results are positive in the short-term, little is known about the long-term effects of this diet on cardiovascular disease risk. Furthermore, these studies did not evaluate the impact of this diet on risk factors for other chronic diseases, such as osteoporosis. The purpose of this research study was to evaluate the accuracy of the nitroprusside test to assess ketone status by comparing results with serum ?-hydroxybutyrate concentration and to determine whether ketones associated with weight loss (Chapter 3); and to comprehensively examine the effect of a LCHP diet on bone status by analyzing changes in calcium metabolism, biomarkers of bone turnover, and bone mineral status over 12 weeks (Chapter 4).
Osteoporosis is predominant in women because less bone is accrued during the developmental years and bone loss begins earlier in life. Furthermore, dietary intake of key micronutrients, such as calcium, tends to be inadequate in women, particularly in women who are dieting. The prevalence of obesity is greater among women (28.4%) compared to men (23.7%) (8), which may lead to more frequent dieting behaviors among women. In fact, data show that 45% of women are dieting at any given time, compared to 30% of men (9). Because women are more likely to exhibit dieting behavior, they are at greater risk for participating in dietary interventions that may stimulate bone loss. Careful examination of the influence of weight loss diets on bone health is vital for ensuring individuals are not placing themselves at risk for osteoporosis.
The claim that LCHP diets promote bone loss was spurred from previous investigations that demonstrated high dietary protein intake induced hypercalciuria (10, 11). The sulfur-amino acids released from protein metabolism reduce systemic pH by simultaneously increasing extracellular hydrogen ion concentrations and reducing bicarbonate concentrations. Systemic acidosis is corrected by increased renal acid excretion and bicarbonate reabsorption, which is accompanied by reduced renal calcium reabsorption (12). Because the majority of body calcium is stored in bone and suppressed urinary calcium reabsorption stimulates hyperparathyroidism, the source of the excess urinary calcium is believed to come from bone. However, human studies that have examined the effect of high dietary protein intake on bone status have found discrepant findings.
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Effect of a Low Carbohydrate
