Diets emphasizing restricted carbohydrate and increased protein intake experienced a resurgence in popularity in the US in the late 1990’s and early 2000’s. While consumer interest in these diets has since begun to wane, a number of recent studies have demonstrated the efficacy of a high protein intake combined with moderate intakes of fat and carbohydrates (30% protein, 20-30% fat, 40-50% carbohydrate) in weight loss, appetite control, and improved blood glucose levels. However, there remains conflicting evidence regarding the impact of a high protein intake on overall kidney health, which extends to acid-base balance and bone health.

An increase in protein intake has been shown to increase renal plasma flow and to increase the glomerular filtration rate (GFR). It is accepted that glomerular hyperfiltration resulting from consumption of a high-protein diet can cause progressive kidney damage in people who already suffer from kidney disease; however there is controversy over the effects of a high-protein (HP) diet in those with healthy kidney functio. Additionally, HP diets produce a marked acid load in the form of excess sulfates from the metabolism of sulfur-containing amino acids. To maintain acid-base homeostasis the kidney increases its excretion of the acid load, and any failure on the part of the kidney to excrete the acid will lead to metabolic acidosis. Because aging is associated with a decline in kidney function, in the form of decreased GFR and decreased ability to excrete acid, examining the effects of a HP diet in older people is of particular interest.