It has recently been established that the rate of progression of
chronic renal failure in man can be slowed by restricting
dietary protein. Consequently, the short term and long term effects of a
low protein diet on the course of different chronic nephropathies were studied in an attempt to delineate the factors that determine the response to such a diet. When a
low protein diet was given for six months renal function improved significantly in nine patients with chronic
tubulointerstitial nephritis (p less than 0.025); the diet had a marginally beneficial effect in 12 patients with chronic
glomerulonephritis (p less than 0.05) and no effect in nine with hypertensive
nephrosclerosis. The heterogeneous functional response in the patients with chronic
glomerulonephritis correlated closely with the effect of the diet on these patients'
proteinuria (r = 0.76, p less than 0.01). In a short term study (four weeks) of 12 patients with
chronic renal failure changes in renal plasma flow were proportional to
dietary protein intake. Renal vascular resistance fell during a
high protein diet and increased when
dietary protein was restricted. The changes in renal plasma flow during the
low protein diet correlated well with the patients' long term functional response to the diet (r = 0.76, p less than 0.01). It is concluded that the response to a
low protein diet in
chronic renal failure is determined, firstly, by the nature of the underlying nephropathy, with maximal benefit being observed in non-glomerular disorders; secondly, by the effect of the diet on the
proteinuria in chronic
glomerulonephritis; and, thirdly, by the haemodynamic response to the diet, with patients with a reactive renal vascular bed improving with a
low protein diet.