"No Red Meat" Helps Diabetic Kidneys

Summarized by Robert W. Griffith, MD
July 3, 2006

Summary

Kidney damage in people with type 2 diabetes can be slowed by switching from red meat (beef) to chicken meat

Introduction

Four in ten type 2 diabetic patients will develop nephropathy - a diabetic complication involving the kidneys, which, if not controlled, may lead to end-stage-renal-disease, requiring dialysis and eventually a kidney transplant. One of the most important signs of diabetic nephropathy (DN) is the appearance of albumin (a protein) in the urine in measurable quantities. The urinary albumin excretion rate (UAER) is used to diagnose the condition, and to check on its progress; normally, it should be less than 200 micrograms of albumin a minute. This is usually accompanied by abnormal blood lipid levels - raised blood cholesterol and triglyceride levels.

Diabetic nephropathy can be slowed, and end-stage renal disease postponed, by consuming a low protein diet. And a high intake of fish protein apparently has a protective effect in type 1 diabetic patients. Now investigators from Brazil have reported in the American Journal of Clinical Nutrition on their results of withdrawal of red meat from the usual diet in type 2 diabetic patients. Here's a summary.

What was done

Patients with type 2 diabetes were selected for this study; they had to be under 75 and have a body mass index (BMI ) below 32, UAER over 200 micrograms per minute, and raised serum triglyceride levels. People with abnormal liver function, uncontrolled diabetes, and urinary or renal infections were excluded. This was a cross-over study - that is to say, the same patients received all three treatment regimes, one after the other, in a randomly selected order. There was a 2-month run-in period, during which their usual diet and diabetic medication regimes were stabilized.

The three dietary regimes were: usual diet (UD), low-protein diet (LPD), and chicken diet (CD). All three diets all had the same amount of energy (calories) and proportion of fat (30% of calories). The UD and CD had the same total amounts of protein (20% of calories), with all the meat in the UD replaced by dark chicken meat for the CD. The protein in the LPD was at least 50% below the usual protein content of each patient's UD and CD, and consisted of dairy and vegetable protein only.

Each diet was followed for 4 weeks, followed by a 4-week washout period on their UD, followed by the next diet for 4 weeks, another washout period, and then the final diet. At the end of each 4-week diet phase, the UAER, the glomerular filtration rate (GFR, a measure of renal function), serum lipid profile, and blood pressure were measured.

What results were obtained

Although 67 patients were invited to participate, only 40 entered the run-in period - the others refused as they disliked chicken or red meat. Of the 40 run-in patients, only 17 completed the long, complicated protocol fully.

The average age was 59, the average BMI was 26, and 14 of the participants were men. The protein intake was similar with the CD and UD, and lower with the LPD, as expected; the amount of chicken eaten daily during the CD phase was almost the same as the amount of meat eaten during the UD (173 g/day vs. 188 g/day). Both the CD and the LPD produced a significant decrease in albuminuria; the UAER fell from an average of 312 micrograms/minute on the UD to 269 and 229 micrograms/minute on the CD and LPD, respectively.

Other improvements on the CD and LPD were an increase in the serum polyunsaturated fatty acids (PUFAs), compared to the saturated fatty acids, and changes in the lipid profile, compared with the UD - serum low density lipoprotein (LDL) cholesterol and triglycerides were decreased significantly. Glomerular filtration rate and HDL cholesterol were not affected.

What these findings mean

Previous studies have already shown that a low protein diet can reduce albuminuria in type 2 diabetics with nephropathy. However, this study addresses an additional aspect of the protective measure - switching from a low protein diet to a 'no-red-meat' diet. The results clearly support the concept: the CD was as effective in lowering the UAER as the LPD (and, probably, was more palatable to many of the participants).

The investigators provide an explanation for the beneficial renal effect of the chicken over red meat. They suggest that it's related to the lower serum PUFA levels found with the CD. Red meat has a high level of saturated fatty acids, so that its withdrawal and substitution with chicken increases the proportion of PUFAs in the blood. Low PUFAs are known to be a risk factor for coronary artery disease in men, whereas high levels provide some protection, possibly by an effect on the endothelium - the cells that line the arteries and which are the first to show atherosclerosis changes. Improved blood flow in the kidney tissues allows the glomerular filtration rate to increase and albuminuria to decline.

Another possible explanation concerns certain aminoacids found in red meat, namely arginine and glycine, which are known to influence renal function. However, it should be noted that the only dietary recommendation that can be made for these patients, based on the findings here, is to restrict beef intake. This will have a beneficial effect on known markers of diabetic nephropathy - i.e. raised UAER, lowered GFR, and low PUFA:saturated fatty acid ratios.

Source

• Withdrawal of red meat from the usual diet reduces albuminuria and improves serum fatty acid profile in type 2 diabetes patients with microalbuminuria. VDF. de Mello, T. Zelmanovitz, MS. Perassolo ,  et al., Am J Clin Nutr, 2006, vol. 83, pp. 1032--1038

Related Links
WebMD: Diabetic Nephropathy - topic overview
University of Maryland: Diabetic Nephropathy
Early Intervention in Diabetic Nephropathy is Key

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