Vegetarian compared with meat dietary protein source and phosphorus homeostasis in chronic kidney disease.

BACKGROUND AND OBJECTIVES: Patients with advanced chronic kidney disease (CKD) are in positive phosphorus balance, but phosphorus levels are maintained in the normal range through phosphaturia induced by increases in fibroblast growth factor-23 (FGF23) and parathyroid hormone (PTH). This provides the rationale for recommendations to restrict dietary phosphate intake to 800 mg/d. However, the protein source of the phosphate may also be important. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We conducted a crossover trial in nine patients with a mean estimated GFR of 32 ml/min to directly compare vegetarian and meat diets with equivalent nutrients prepared by clinical research staff. During the last 24 hours of each 7-day diet period, subjects were hospitalized in a research center and urine and blood were frequently monitored. RESULTS: The results indicated that 1 week of a vegetarian diet led to lower serum phosphorus levels and decreased FGF23 levels. The inpatient stay demonstrated similar diurnal variation for blood phosphorus, calcium, PTH, and urine fractional excretion of phosphorus but significant differences between the vegetarian and meat diets. Finally, the 24-hour fractional excretion of phosphorus was highly correlated to a 2-hour fasting urine collection for the vegetarian diet but not the meat diet. CONCLUSIONS: In summary, this study demonstrates that the source of protein has a significant effect on phosphorus homeostasis in patients with CKD. Therefore, dietary counseling of patients with CKD must include information on not only the amount of phosphate but also the source of protein from which the phosphate derives.

Racial differences in skeletal calcium retention in adolescent girls with varied controlled calcium intakes.

BACKGROUND: Higher bone mass in blacks than in whites has been related to greater calcium utilization efficiency. Dietary calcium requirements for maximal skeletal calcium accretion during puberty may differ between the races. OBJECTIVE: This study compared the relation between calcium intake and calcium retention in black and white adolescent girls. DESIGN: A range of controlled calcium intakes (760-1981 mg Ca/d) were used in 3-wk controlled balance studies. Some subjects were studied more than once; a total of 182 observations from 55 black girls and 66 white girls were analyzed. RESULTS: Blacks had 185 +/- 32 mg/d greater mean skeletal calcium retention than did whites (P < 0.0001) at all calcium intakes as a result of significantly greater net calcium absorption (P < 0.001) and lower calcium excretion (P < 0.0001). CONCLUSIONS: Dietary calcium requirements did not differ with race. Higher calcium retention at all calcium intakes during adolescence may underlie the higher bone mineral content of adult blacks than of adult whites.

Racial differences in calcium retention in response to dietary salt in adolescent girls.

BACKGROUND: Sodium is an important determinant of urinary calcium excretion, and race is an important determinant of calcium retention. The effect of dietary sodium on calcium retention and the influence of race have not been studied in adolescence, the life stage during which peak bone mass is accrued. OBJECTIVE: The study reported here was undertaken to compare racial differences in calcium retention as a function of dietary salt intake. DESIGN: A total of 35 adolescent girls (22 black and 13 white) participated in two 20-d metabolic summer camps, separated by 2 wk, that simulated a free-living environment. The effect of changes in dietary sodium on calcium retention was tested in a randomized-order, crossover design with 2 concentrations of sodium-1.30 g/d (57 mmol/d) and 3.86 g/d (168 mmol/d)-and a constant calcium intake of 815 mg/d (20 mmol/d). RESULTS: Both race and sodium intake significantly affected calcium retention (P < 0.01). Calcium retention was significantly greater in black girls than in white girls, regardless of dietary sodium intake (P < 0.001). The high-sodium diet significantly reduced calcium retention in both whites and blacks (P < 0.01), primarily through a decrease in net calcium absorption. Black girls excreted significantly less calcium in the urine than did white girls, regardless of diet (P < 0.05). CONCLUSIONS: Calcium retention is significantly greater in black girls than in white girls but is significantly reduced in girls of both races in response to salt loading.