This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.Although it has been established that high-protein diets result in the generation of excess acid load and that the kidney's ability to eliminate that excess acid is reduced as a consequence of aging, the effects of high-protein diets on systemic acid base balance in older populations have not been studied. The purpose of this study is to examine the effects of a high-protein, low-carbohydrate diet on acid-base balance and renal calcium excretion in older (aged 55-70) compared to younger (aged 25-40) adults. A total of 24 healthy subjects (12 older and 12 younger) will participate in this 6-week feeding study. This crossover study design consists of two cycles, both of which are comprised of a 2-week 'washout' (usual) diet followed by a 1-week experimental diet, either high or low in protein (2.0 or 0.5 g protein/Kg body weight). During the washout period the subjects will consume and record their self-selected usual diet. During the experimental diet the subjects will consume the metabolic meals provided to them. The fat, calcium, phosphorous, sodium, and potassium content of the diet will remain the same while only protein and carbohydrate content varies. Fasting blood and urine samples and 24-hour urine samples will be collected a total of four times over the course of the study. Differences in acid excretion, serum acidity, and calcium excretion as a function of age and in response to the high-protein, low-protein, and usual diet will be compared and analyzed using an Analysis of Covariance.
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