THE INFLUENCE OF DIETARY FACTORS ON URINARY CALCIUM EXCRETION: AN INVESTIGATION OF PROTEIN, POTASSIUM BICARBONATE AND PHOSPHATE USING AN ACUTE LOAD TEST IN ADULT MALES
Date
1996-03
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ORCID
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Degree Level
Masters
Abstract
High protein diets have been shown to promote negative calcium balance by increasing calcium excretion in urine. However, as protein in the diet increases, so does the phosphate content which accompanies the protein. Phosphate reduces calcium excretion in the urine. The addition of potassium bicarbonate has been shown to reduce urinary calcium losses. This study was set up to examine the acute effects of protein, phosphate and potassium bicarbonate on urinary calcium. We examined the usefulness of an acute load test as a method to study dietary effects on calcium balance.
Ten healthy adult males were randomly fed 50 g protein (HP), 50 g protein + 50 mmol potassium bicarbonate (HP+K), 17 g protein (MP), or 17 g protein + 8 mmol phosphate (MP+Pi). The additional phosphate was equivalent to the amount contributed by 33 g of protein. The protein used was milk protein (80% casein, 20% lactalbumin). Urine was collected at baseline and every 1.5 hours postload for 4.5 hours. Blood was taken at baseline and at 3 hours postload.
There were no significant differences in urinary calcium excretion (UCa) at baseline between all treatments. At 3 hours postload, the HP treatment resulted in hypercalciuria in subjects compared to during the MP+Pi treatment (p<0.05). Equalizing phosphate was shown to be necessary in demonstrating the hypercalciuric effect of protein since UCa during the HP treatment was not significantly different from the MP treatment. The addition of potassium bicarbonate (HP+K) resulted in a significant lowering of UCa in subjects compared to the HP treatment (p<0.05). The HP+K treatment resulted in a significantly higher urinary potassium excretion in subjects at 1.5 hours and 3 hours postload compared to during the HP treatment (p<0.05). As well, the HP+K treatment resulted in a significantly higher urinary sodium excretion in subjects at 3 hours and a significantly lower urinary phosphate excretion in subjects at 3 hours compared to during the HP treatment (p<0.05). Acid excretion in the urine and serum parathyroid hormone (PTH) was measured at baseline and 3 hours postload. There were no significant differences in NAE at baseline between all treatments. The HP treatment resulted in a significantly higher net acid excretion (NAE) at 3 hours compared to the MP (p=0.0005) and MP+Pi (p=0.0054) treatments. Supplemental potassium bicarbonate resulted in a
significant lowering of NAE at 3 hours compared to during the HP treatment. There were no significant differences between treatments for serum PTH when measured at baseline and 3 hours.
The results obtained in the present study were similar to those of chronic load tests. When HP was compared to MP+Pi, HP was shown to be hypercalciuric. When phosphate levels were not equal (MP vs HP), there was no apparent hypercalciuric effect. The addition of potassium bicarbonate reduced UCa due to HP and also caused a significant increase in natriuresis and a significant decrease in phosphaturesis. Net acid excretion was shown to be a factor involved in the hypercalciuria of protein; however, there was no evidence for the involvement of serum PTH. The acute load test is useful for studying the effects of dietary factors such as protein, phosphate and potassium bicarbonate on urinary calcium excretion.
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Keywords
DIETARY FACTORS, URINARY CALCIUM EXCRETION
Citation
Degree
Master of Science (M.Sc.)
Department
Pharmacy and Nutrition