Isolated soy protein consumption reduces urinary albumin excretion and improves the serum lipid profile in men with type 2 diabetes mellitus and nephropathy

Soy protein was shown to exhibit several beneficial effects on renal function in nondiabetic patients with nephropathy, and to improve serum lipids. This study examined the effects of isolated soy protein consumption on urinary albumin excretion, serum lipids, plasma amino acids, and isoflavones in diabetic patients with nephropathy. Male patients (n = 14) with type 2 diabetes and nephropathy were followed in a crossover design for 7 mo. The study comprised two 8-wk intervention periods, placed between a 4-wk lead-in and two 4-wk washout periods. In the 2 intervention periods, 0.5 g/(kg · d) of the dietary protein was provided as either isolated soy protein (ISP) or casein, in random order. Blood and urine samples were collected at the beginning and end of each period. Data were analyzed by multiple linear regression for a repeated-measure design. ISP consumption led to changes of -9.5% in urinary albumin excretion (P < 0.0001), -0.45 in the total-to-HDL-cholesterol ratio (P < 0.05), -0.20 in the LDL-to-HDL cholesterol ratio (P < 0.05), and +4.3% in HDL cholesterol (P = 0.0040). Plasma arginine concentrations, the arginine-to-lysine ratio, and plasma isoflavone concentrations were higher after ISP consumption (P < 0.05). Urinary albumin excretion was negatively correlated with plasma total isoflavones (p = -0.441), daidzein (p = -0.326), and O-desmethylangolesin (p = -0.389) (P < 0.05). The findings indicate that isolated soy protein consumption improves several markers that may be beneficial for type 2 diabetic patients with nephropathy.