April: Are High-Protein, Vegetable-Based Diets Safe for Kidney Function? A Review of the Literature

As more than 60% of adults in the US aged 20-74 years are overweight or obese, many CKD patients are not only faced with dietary modifications in order to help manage their disease, but also to reduce weight. Popular weigh loss diets today encourage increasing protein intake and decreasing carbohydrate intake. These diets can pose problems for patients with CKD because high protein intake may accelerate CKD. This problem presented the question in the continuing education article in this month’s Journal of the American Dietetic Association. The article, Are High-Protein, Vegetable-Based Diets Safe for Kidney Function? A Review of the Literature, reviews literature to date comparing the effects of animal and vegetable protein on kidney function in health and disease. Since it has long been proposed and studied that a high animal protein diet accelerates complications seen in CKD, a review of literature studying the effects of non-animal protein was needed. The literature shows that the long-term effects of high protein intake are unknown or poorly understood both in normal renal function as well as chronic kidney disease. High-protein diets pose particular problems for patients with CKD because high protein intake may accelerate CKD, however, patients with CKD are at high risk for protein malnutrition. Among other findings, the review suggests that vegetable protein diets appear to meet protein requirements and provide adequate nutrition in people with CKD, and that high protein intake, from either vegetable or animal source, likely accelerates CKD.

Traditionally, one of the main dietary modifications used to help delay or prevent the advancement of CKD is dietary protein restriction. This stems from the long known consequence that ingesting too much protein accumulates waste products, such as nitrogen-containing compounds, acids, phosphates, uric acid, oxalate, and phenols, which can accelerate renal deterioration. The second article, Dietary Protein Restriction Benefits Patients with Chronic Kidney Disease, outlines the need for safe methods of management such as dietary manipulation. The article points out that protein restriction has not been proven to slow the progression of CKD. However, most CKD symptoms are caused by protein intolerance, therefore protein restriction can reduce albuminuria and prevent uraemic symptoms. The article also suggests that a properly designed low-protein diet maintains body weight and protein stores even in patients with advanced CKD. Furthermore, it is explained that malnutrition is believed to be so common in CKD due mainly to a problem with definitions. Malnutrition refers to abnormalities caused by an insufficient or imbalanced diet, and should be cured by increasing dietary protein. According to the article the metabolic problems attributed to malnutrition in CKD patients are caused by complications of CKD rather than an inadequate diet. The adverse effects occur when the diet exceeds the ability of the damaged kidney to excrete the ions and metabolic products and can be present with only a mild increase in some of these products. The presence of protein intolerance explains why limiting dietary protein will ameliorate the symptoms of CKD.

While low-protein diets have been advocated for over 70 years as a means of slowing the rate of progression of kidney disease and delaying the appearance of uraemic symptoms, the practice has recently come under scrutiny. The third article, Dietary Protein Restriction as a Treatment for Slowing Chronic Kidney Disease Progression: The Case Against, reviews several reasons why the benefit to risk ratio of dietary protein restriction is not favorable for many reasons, including compliance is generally sub-optimal, there is no convincing clinical evidence that dietary protein restriction provides any benefit beyond that afforded by angiotensin blockade, and the optimal level and duration of dietary protein intake have not been defined. This article also suggests that there is concerning evidence that low-protein diets are associated with both statistically and clinically significant declines in nutritional markers in CKD populations, which already have a high prevalence of malnutrition. Finally, the article concludes that patients with progressive renal failure are likely to be better served by ensuring optimal preservation of their nutrition and instituting alternative, proven measures for which there is a much stronger body of clinical evidence of favorable benefit to risk ratio, such as rennin-angiotensin system blockade, blood pressure reduction and statin therapy.

ADA Continuing Education Research Article:
Bernstein, Adam M. "Are High-Protein, Vegetable-Based Diets Safe for Kidney Function? A Review of the Literature." Journal of the American Dietetic Association 107.4 (2007):644-.

Additional Articles:
Mandayam, S. "Dietary protein restriction benefits patients with chronic kidney disease." Nephrology 11.1 (2006):53-7.

Johnson, DW. "Dietary protein restriction as a treatment for slowing chronic kidney disease progression: the case against." Nephrology 11.1 (2006):58-62.

All articles and the JADA Continuing Education Questionnaire can be found at www.adajournal.org.