Effect of Milk Proteins with or without Salts on Urinary Calcium Excretion in Premenopausal Women Following an Acute Load Test
Date
1994-12
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ORCID
Type
Degree Level
Masters
Abstract
Milk and milk products contain factors that may act to increase or decrease urinary calcium excretion (UCa). Milk contains casein, low in sulfur amino acids, and lactalbumin, higher in sulfur amino acids. The presence of sulfur amino acids are responsible for calcium losses in urine. Milk also contains potassium which may decrease UCa. Cheddar cheese contains casein and NaCl. Sodium chloride has been shown to increase UCa, therefore cheddar cheese may promote UCa. Two studies were completed to examine the usefulness of acute load tests to determine the effects of dietary factors found in dairy products on UCa.
The effect of adding moderate levels of dairy proteins and salts found in milk (casein, C and lactalbumin, L with or without KHCO3), cheese (C and NaC1) or a non-dairy protein on UCa following 5 acute loads was determined in Study 1. Seventeen grams of milk protein (MP; 80% C, 20% L), 17 g MP + 23 mmol KHCO3 to simulate "milk" (MPK), 17 g casein + 23 mmol NaC1 to simulate "cheese" (CH), 17 g carbohydrate (CHO) and 17 g egg white (EW) were tested. Ten premenopausal women consumed each treatment following collection of fasting urine and serum samples. Urine samples were then collected 1.5 hours and 3 hours postload and an additional serum sample 3 hour postload.
By hour 3 all of the treatments except MPK caused a significant rise in UCa. Moderate amounts of protein did not increase UCa relative to CHO. Due to inconsistent fasting values in Study 1 the three treatments containing milk proteins were repeated. Three treatments were added containing 50 g of milk protein as 50 g milk proteins (Hi-MP), 50 g MP + 70 mmol KHCO3 (Hi-MPK) and 50 g casein + 70 mmol NaC1 (Hi-CH). As well, the subjects (10 premenopausal women) were required to consume a controlled diet after 3 pm 11the day prior to each load test to decrease any carry over affects.
In Study 2, all of the treatments except Hi-MPK and Hi-CH increased urinary calcium excretion over the three hours. Phosphate excretion was significantly lower for Hi-MPK compared to Hi-MP and Hi-CH, even though all three treatments contained the same amount of phosphate. Serum phosphate rose after Hi-MP or Hi-CH treatment but not for Hi-MPK.
It appears that KHCO3 prevents a rise in both calcium and phosphate excretion but only at high levels since MPK had no hypocalciuric or hypophosphatiuric effects. A hypercalciuric affect of excess milk proteins alone was not observed. Subjects given MP and Hi-MP did not differ in UCa, but Hi-MP contained more phosphate than MP which could account for the lack of a hypercalciuric affect.
In both studies, we were able to see a proportional rise in potassium excretion when subjects were given MPK and Hi-MPK treatments, but additional dietary sodium was not detected in the urine during the CH or Hi-CH treatments. Therefore the 3 hour acute load test is a suitable method for determining the effect of protein and KHCO3 on UCa, but is not useful for examining the effects of NaCl and UCa.
Description
Keywords
urinary calcium excretion
Citation
Degree
Master of Science (M.Sc.)
Department
Pharmacy and Nutrition