What have isotope studies in humans told us about the nutritional effects of acidosis in dialysis?

In order to understand how acidosis might predispose to loss of lean body m ass it is important to recognise that body protein is in a dynamic state wi th a daily turnover of approximately 300 g of protein in a 60 kg man. This is significantly greater than the daily protein intake at a level of 1 g . kg(-1) . day(-1). Loss of lean body mass occurs when the balance between wh ole body protein synthesis and breakdown is negative. Measurement of whole body protein turnover is possible using either boluses or primed constant i nfusions of isotopically labelled amino acids. Previously, a variety of in vitro and in vivo animal studies have shown that acidosis increases protein degradation and amino acid oxidation. Several research groups including ou r own have used amino acid tracer techniques to examine whether protein deg radation is increased in vivo in human subjects with acidosis and chronic r enal failure. The results from these studies have shown a remarkable concor dance with increased protein degradation in all groups of patients studied. However, the results for protein synthesis have been more difficult to int erpret, with only a few studies directly measuring the effects of acidosis on amino acid incorporation into protein.