Kidney disease is one of the most feared complications for patients with diabetes. Unfortunately, this condition is all too common and the numbers continue to grow. The good news is that it can be identified with routine screening and that aggressive treatment will delay its progression to ESRD (end-stage renal disease). There are five stages of diabetic kidney disease. These stages lead to a progressive reduction in glomerular filtration rate and increased levels of albumin in the urine. Microalbuminuria progresses over time to macroalbuminuria (defined as a urine albumin excretion rate of over 300 mg in 24 hours) and this defines nephropathy. This article will explore the risks for diabetic kidney disease, screening as well as treatment strategies.
Risk factors for diabetic kidney disease
- Genetics – It is known from the Diabetes and Complications trial (DCCT) that some groups have a higher risk of diabetic kidney disease despite reasonable glycemic control (1). This increased risk appears to be associated with parental history of hypertension, diabetes and cardiovascular disease.
- Glycemic control – Research has shown that higher levels of glucose (increased HbA1C) will cause early stages of kidney disease. Also, higher glucose levels will hasten the progression of kidney disease (1). Achieving an HbA1C of 7% is important for patients with diabetes. A lower target may be considered in some patients if this does not increase their risk of hypoglycaemia. This will likely involve multiple daily injections (MDI)/or pump in patients with type 1 diabetes and using multiple medications or insulin earlier in patients with type 2 diabetes.
- Duration of diabetes – This appears to be a consistent risk factor for diabetic kidney disease.
- Blood pressure – Blood pressure should be targeted to 130/80. Strategies should include lifestyle modifications (achieving and maintaining an ideal body weight, limiting sodium to 1500 mg per day and alcohol intake according to CDA guidelines) as well as blood pressure medications if targets are not achieved. ACE inhibitors and ARB’s both offer renal protection. In type 2 diabetes ARB’s have been found to delay time to dialysis in those with diabetic nephropathy (2). Additional drugs should be added if BP targets are not met. Multiple drugs (>3) are often needed to meet targets. Hyperkalemia can be a complication of ACE/ARB therapy and a potassium restricted diet will help lower levels. High potassium foods include potatoes, oranges, bananas, grapefruit and tomatoes. The side effect of cough with ACE therapy may necessitate a switch to ARB therapy.
- Other risk factors – These include male sex, total cholesterol and smoking and ethnicity. Patients with diabetic kidney disease have an increased risk of cardiovascular disease. It has been noted that patients with diabetic kidney disease have more atherogenic lipid profiles (1). Achieving the CDA lipid targets will help reduce this risk. Smoking has consistently been found to worsen the progression of kidney disease (1). There is also an increased risk of kidney disease in Black, Hispanics and First Nations patients.
Screening – The standard screening tool for kidney disease is the albumin/creatinine ratio (ACR). It should be done annually in patients with type 1 diabetes after 5 years duration and at diagnosis in type 2 diabetes and annually thereafter. Unfortunately we know that type 2 diabetes can go undiagnosed for as long as 8-10 years. Also, it may take many patients 5 or more years to get serious about their disease. Good control at the onset of diabetes does reduce the risk of kidney disease.
Treatment Through Diet
A. Protein –The role of protein restriction is controversial. The CDA recommends that protein intake be no different from the person without diabetes. There have been many studies which have investigated the use of different levels of protein in the diet. Some of the earlier studies have found an improvement in the decline of kidney function but were of short duration and with a small number of subjects (1). A recent meta-analysis in 2008 (3) concluded that a low protein diet was not associated with a significant improvement in kidney function in patients with type 1 or 2 diabetes and diabetic kidney disease. The American Diabetes Association clinical practice guidelines (2008) suggest 0.8 -1.0 g/kg body weight/day in individuals with diabetes and a reduction to 0.8g in the later stages of kidney disease. A good starting point is to assess current intake and then to make appropriate recommendations. See sample diet history for some simple dietary strategies. It is important that nutritional intake not be compromised and those good quality proteins help to make up the diet. Good quality proteins include milk, fish, eggs, meat and soy. Some patients use protein powders and bars liberally and this should be discouraged. High protein weight loss diets are still popular among some patients with diabetes and if used at all should be only short-term.
B. Protein type – There have also been studies which investigated types of protein on kidney function. In one study the replacement of red meat with chicken reduced the urinary albumin excretion rate in type 2 patients with kidney disease and had a similar effect to an ACE inhibitor (4).
C. Omega-3 fatty acids – Some researchers have suggested an omega-3 fatty acid rich diet (rich in canola oil) decreases excretion of urine albumin in laboratory animals (5).
- Glycemic control – It is clear that early and aggressive lowering of blood sugar is important to long-term health of the kidneys.
- Blood pressure control – Optimal blood pressure control through lifestyle/medication(s) is critical. Sodium restriction is important as many patients with diabetes are salt sensitive.
- Diet – The dietitian can decide with the patient how best to plan the diet. Issues to address include protein, sodium, distribution and heart health.
- Psychological impact – Patients will be distressed by the effect of diabetes on their kidney function and information should be conveyed in a sensitive and positive manner. Diabetes is a burden and kidney disease adds to this burden. It is important to remember that it really was not until the mid-90’s that many health professionals were even convinced that good control mattered. Many of our patients with years of diabetes did not have the tools to properly manage their diabetes that we have today. Now there is much we can offer patients to maintain kidney function and delay time to dialysis.
|Breakfast||2 egg omelette with cheese, 2 buttered toast, orange juice, coffee with cream||1 egg omelette with skim milk cheese (1 oz), toast with heart healthy margarine, orange juice and coffee with 2% milk|
|Lunch||Roast beef sandwich (4 oz beef), mayo, cream soup and fat-free yoghurt||chicken/tuna/salmon sandwich (2 oz), low-fat mayo, vegetable soup and fat-free yoghurt|
|Snack||4 oatmeal cookies, apple juice||2 oatmeal cookies, fresh apple|
|Dinner||6 oz chicken, home fries, corn, ice-cream||3-4 oz chicken, baked potato, corn, extra green vegetables, frozen yoghurt|
|Snack||2 oz cheese and crackers||crackers and peanut butter (1 tbsp)|
- Gerstein HC, Haynes RB. Evidence-Based Diabetes Care 2001:429-465.
- Canadian Diabetes Association 2008 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada: S126-133.
- Pan Y, Guo LL, Jin HM. Low-protein diet for diabetic nephropathy: a meta-analysis of randomized controlled trials. Am J of Clin.Nutr. 2008.88(3):660-6.
- De Melo VD et al. Long-term effect of a chicken-based diet versus enalapril on albuminuria in type 2 diabetic patients with microalbuminuria.2008.J of Renal Nutrition.18(5):440-7.
- Garman JH et al.Omega-3 fatty acid rich diet prevents diabetic renal disease.2009.Am J of Physiology.296 (2):F306-16.