A diet high in protein has been shown to accelerate the progression of kidney disease. For this reason, health professionals have for many years recommended that those individuals at risk for, and being treated for, renal disease modify their diet to limit the amount of protein that is consumed. This is a particularly difficult challenge for Americans who tend to consume protein in excess of dietary needs (1). The current recommendation is that pre-dialysis kidney disease patients limit their protein intake to 0.6 ­ 0.8 g/kg of body weight. However, individuals suffering from kidney disease should talk with their physician and registered dietitian to formulate a diet specific for their condition.

On the basis of available evidence, a diet that is low in protein has been shown to have beneficial effects on kidney function. These same benefits may be seen with a soy- protein based meal plan. The soy-protein hypothesis predicts that substituting soy protein for animal protein in patients with diabetes may protect this population from developing diabetic nephropathy (2). It appears that soy protein helps to normalize glomerular filtration rates (GFR) and renal plasma flow. GFR is often used as a clinical marker to measure kidney health.

Soy in the prevention of diabetic kidney disease
Approximately one-third of all individuals with diabetes will develop kidney disease; those with type 1 diabetes are at particularly high risk. Unfortunately, diabetic kidney disease, also called diabetic nephropathy, can eventually worsen to end-stage-renal disease. For this reason, health professionals recommend that those with both type 1 and type 2 diabetes take precautionary steps to prevent the onset of this debilitating condition. In particular, dietary protein restriction has been implemented in the diet of these individuals. Research is now focussing on the role that a diet rich in soy-protein may have in preventing the onset of diabetic nephropathy.

There is limited published research on the impact of soy-protein in patients with kidney disease. In 1989 Nakamura and collaborators examined the effects of different protein loads on renal function. They found that when comparing a tuna-meal to a soy-protein meal the tuna meal led to a significant increase in GFR while the GFR in the soy-protein meal remained constant (3). In addition, Kontessis et al showed that renal blood flow, GFR and the fractional clearance of albumin were all lower after 3 weeks on a soy-protein based diet, as compared to a meat-based diet (4). Similarly, Reilla and colleagues have reported that replacing soy-protein with animal-protein produces a smaller increase in GFR and therefore helps to prevent kidney damage (5).

Most recently, Anderson et al evaluated how a diet rich in soy-protein effects renal function in type 2 diabetes patients with obesity, hypertension and proteinuria. Subjects followed either a control or soy diet each providing 1 g protein/kg body weight. In the soy diet 50 % of the total protein came from soy foods. A significant decrease in serum cholesterol and triacylglycerols was found when subjects consumed the soy diet. However, no distinct effects on renal function or proteinuria were reported (2). Further research is needed to fully evaluate how a diet rich in soy-protein effects renal function in type 1 and type 2 diabetes.

Incorporating soy into the diet
At this time we feel it is safe to recommend that individuals at risk for developing kidney disease, secondary to their diabetes, try to incorporate one or two servings of soyfoods into their daily diet. These soy protein sources do not appear to have the same negative impact on kidney health as do their animal protein counterparts. One serving of soyfood can be used in the diabetic exchange meal plan as one protein exchange. Soy cheese and regular soy milk will also add one fat exchange. Due to the prevalence of obesity among type 2 diabetic individuals, and the relatively high fat content of some soy products, these individuals should be encouraged to use low-fat and non-fat soy alternatives. In particular, many tofu and soy beverage varieties come with varying amounts of fat. These products are generally readily available and offer a high quality soy protein with little change in product flavor or palatability.