High levels of urine protein are a red flag for kidney disease. For reasons that remain unclear, inflamed kidneys have problems filtering protein. Protein leaks through the kidney filters, called glomeruli, instead of remaining in the blood. This condition is called proteinuria. Very severe proteinuria is called nephrosis. Independent of any other factor, proteinuria damages the kidney. Physicians occasionally try to compensate for high urine protein by advising that patients eat less protein.
Controversy
Although conventional wisdom advises protein restriction in kidney patients, data is conflicting as to whether this has any positive benefit or not. A 2010 meta-analysis published in the "Cochrane Reviews" shows a statistically insignificant improvement in extending the life of the kidney. Comparable results were published in the "American Journal of Clinical Nutrition" in 2006. This is directly at odds with a 1998 paper published by nephrologist Gerald Appel in the 1998 Baylor University Medical Center Proceedings, which claimed an unequivocal benefit in protein restriction.
Recommendations
The National Kidney Foundation recommends that patients with diabetes who also have chronic kidney disease limit their protein intake to 0.8 grams of protein per kilogram of body weight per day. This is the recommended daily allowance for adults. The NKF notes that this is far less than most people consume; on average Americans eat approximately 1.04 gram of protein per kilogram of body weight. The rationale for this modest restriction is that two meta-analyses have shown the protein restriction reduced the risk of loss of kidney function in diabetes patient.
Warning
The NKF specifically cautions against high-protein diets because such diets increase urine protein--and presumably hasten the loss of renal function. Essentially, the kidneys have to work too hard, in a state called hyperfiltration, to process the increased protein. The NKF specifically warns against the Atkins Diet, the South Beach Diet, Sugar Busters and the Zone.
Children
Many pediatric nephrologists are reluctant to restrict protein in children because protein is essential for growth. For example, nephrologist Sue Conley writes for the Cybernephrology web site for the University of Alberta, saying "I usually only advise avoiding excess protein intake. Children on peritoneal dialysis, who lose protein into dialysate, may actually need a high protein intake to maintain a reasonable serum albumin levels."
Alternatives
The NKF explores possible differences in the type of protein consumed. It noted that several small studies suggest that soy or vegetable protein may not be as hard on the kidneys, even when eaten in the same quantity as protein obtained from red meat. The NKF suggests that non-meat alternatives may be a reasonable alternative for people with stage 1 or stage 2 kidney disease.
References
- Cochrane Reviews: Protein Restriction for Diabetic Renal Disease
- New England Journal of Medicine: The Effect of Protein Restriction
- National Kidney Foundation: Nutritional Management in Diabetes and Chronic Kidney Disease
- The American Journal of Clinical Nutrition: Do Low-Protein Diets Retard the Loss of Kidney Function?
- T. Colin Campbell Foundation: Chronic Kidney Disease
