Dietary flaxseed meal reduces proteinuria and ameliorates nephropathy in an animal model of type II diabetes mellitus.

BACKGROUND: Evidence is emerging that varying the type or source of dietary protein intake can have beneficial effects on chronic renal disease. Consumption of soybean and soy-based food products, as the source of plant protein, can retard the development and progression of chronic renal disease. We studied the obese spontaneously hypertensive/NIH-corpulent (SHR/N-cp) rat, a model of obesity and type II diabetes mellitus that consistently develops nephropathy resembling diabetic nephropathy. We specifically sought to determine whether changing the source of protein intake from animal protein, casein, to plant protein in the form of either soy protein concentrate or flaxseed protein in the diet has a different impact on renal function and nephropathy in this model. METHODS: Male obese SHR/N-cp rats were randomly assigned to one of three diets containing either 20% casein, 20% soy protein concentrate, or 20% flaxseed meal. Except for the protein source, all three diets were identical and contained similar amounts of protein, fat, carbohydrates, minerals, and vitamins. All animals were maintained on these diets for 6 months. At the end of the study, blood sampling and 24-hour urine collections were performed for renal functional measurements, and the kidneys were harvested and examined for histologic evaluation. RESULTS: All three groups had similar amounts of food intake and body weight gain and exhibited fasting hyperglycemia and hyperinsulinemia. Plasma glucose levels did not differ among the three groups, but plasma insulin concentration was significantly lower in rats fed flaxseed meal than those fed either casein or soy protein concentrate. Mean plasma creatinine, creatinine clearance, and urinary urea excretion also did not differ significantly between the three groups. By contrast, urinary protein excretion was significantly lower (P < 0.01) in rats fed flaxseed than in rats fed either casein or soy protein concentrate. Morphologic analysis of renal structural lesions showed that the percentage of abnormal glomeruli with mesangial expansion and the tubulointerstitial score (an index of severity of tubulointerstitial damage) were significantly reduced in rats fed flaxmeal compared to those fed casein or soy protein concentrate. CONCLUSION: We conclude that dietary protein substitution with flaxseed meal reduces proteinuria and glomerular and tubulointerstitial lesions in obese SHR/N-cp rats and that flaxseed meal is more effective than soy protein in reducing proteinuria and renal histologic abnormalities in this model. The reduction in proteinuria and renal injury was independent of the amount of protein intake and glycemic control. Which dietary component(s) present in flaxseed meal is (are) responsible for the renal protective effect remains to be determined.

Dietary flaxseed meal is more protective than soy protein concentrate against hypertriglyceridemia and steatosis of the liver in an animal model of obesity.

OBJECTIVE: Soy protein and flaxseed meal have been reported to have beneficial effects on many chronic diseases in humans and animals. The primary objective of the study was to evaluate the beneficial effects of soy protein and flaxseed meal on hypertriglyceridemia and liver steatosis associated with obesity and diabetes. We compared the effects of dietary soy protein and flaxseed meal with that of casein on plasma and liver lipids in a genetic model of obesity, type II diabetes and insulin resistance, namely the SHR/N-cp rat. METHODS: Lean and obese phenotypes of SHR/-cp rats were fed AIN 93 diets containing 20% of energy from casein (control), soy protein concentrate or flaxseed meal for six months. Plasma was analyzed for total cholesterol, LDL cholesterol, triglyceride and total protein. Liver was analyzed for steatosis by light microscopy after staining samples with Hematoxylin-Eosin and Oil-Red-O. RESULTS: In lean rats soy protein and flaxseed meal significantly decreased plasma total cholesterol (26.0% and 20.3% respectively) compared to casein. In obese rats flaxseed meal had significant cholesterol lowering effect compared to control rats (41%). Soy protein significantly lowered both plasma LDL-cholesterol and HDL-cholesterol in lean phenotypes while in obese phenotypes flaxseed meal significantly lowered LDL-cholesterol and HDL-cholesterol compared to casein-fed rats. Flaxseed meal also significantly lowered plasma triglyceride in both lean and obese rats compared to casein fed rats (33.7% and 37% respectively). There was significantly greater fat accumulation in livers of obese rats than lean rats (200%) regardless of dietary protein type. Flaxseed meal significantly lowered fat deposition in livers of both lean and obese rats compared to rats fed casein or soy protein. Dietary component(s) present in flaxseed meal or soy protein responsible for hypolipidemic effects is not clear. CONCLUSIONS: The marked hypotriglyceridemic and hypocholesterolemic effects of flaxseed meal may have important therapeutic implications in patients with hypertriglyceridemia and hypercholesterolemia and deserve further study in humans with these disorders. Flaxseed meal supplementation may provide a new therapeutic strategy to reduce hypertriglyceridemia and fatty liver.