WASHINGTON — The renal effects of high-protein diets pose a strong risk of harm in patients with chronic kidney disease, Allon Friedman, M.D., said at a meeting sponsored by the National Kidney Foundation.
Chronic kidney disease is often silent, so he recommends obtaining a serum creatinine measurement and a urinary dipstick test for proteinuria in all patients considering a high-protein diet for weight loss.
Those with a glomerular filtration rate of less than 60 mL/min should be advised against a high-protein diet, noted Dr. Friedman of Indiana University in Indianapolis.
Regardless of kidney function, protein intake increases glomerular filtration rate and renal blood flow by as much as 100% from baseline.
Over time, a high-protein diet appears to increase kidney volume and weight.
Studies suggest that high-protein diets increase urinary protein excretion in people with normal and in those with diminished kidney function, Dr. Friedman said.
High-protein diets are intended to induce ketosis by limiting carbohydrate intake. Increased ketone levels lead to increased sodium output, which in turn induces natriuresis, he said.
In the short-term, high protein consumption has been associated with orthostatic hypotension. There is little evidence that high-protein diets maintained for months adversely effect blood pressure, compared with standard low-fat diets.
Animal and human studies have shown that increased protein consumption leads to hyperuricosuria, hypercalciuria, hypocitraturia, and a reduction in urinary pH—all risk factors for the formation of kidney stones.
Healthy patients considering a high-protein diet should be advised about the potentially deleterious effects: chronic glomerular hyperfiltration and hyperemia, increased proteinuria, and an elevated risk for nephrolithiasis, Dr. Friedman said.
It may be helpful, he added, to point out to patients that although short-term studies (3–6 months) have resulted in more weight loss for high-protein diets than for standard diets, long-term studies (up to 1 year) have shown no differences in weight loss between the two groups.