Soy Intake Benefits Patients With Type 2 Diabetes and Nephropathy 

Intake of soy protein had beneficial effects on cardiovascular risk factors and kidney-related biomarkers in patients with type 2 diabetes and nephropathy. Leila Azadbakht, PhD, from the Isfahan University of Medical Sciences in Isfahan, Iran writes, "Several short-term trials on the effect of soy consumption on cardiovascular risks are available, but little evidence exists regarding the impact of long-term soy protein consumption among type 2 diabetic patients with nephropathy."  "To determine the effects of long-term soy consumption on cardiovascular risks, we measured C-reactive protein (CRP) and kidney function indexes among type 2 diabetic patients with nephropathy."

Of 41 patients with type 2 diabetes and nephropathy who were enrolled in this study, 18 were men and 23 were women. The soy protein group (n = 20) was assigned to a diet containing 0.8 g protein/kg body weight (35% animal proteins, 35% textured soy protein, and 30% vegetable proteins), whereas the control group (n = 21) was assigned to a similar diet containing 70% animal proteins and 30% vegetable proteins. Duration of the study was 4 years.

The soy protein group fared better than the control group regarding effects on cardiovascular risk factors. Mean change in the soy protein vs control groups for fasting plasma glucose levels was–18 ± 3 vs 11 ± 2 mg/dL (P = .03); for total cholesterol levels, –23 ± 5 vs 10 ± 3 mg/dL (P =.01); for low-density lipoprotein (LDL) cholesterol levels, –20 ± 5 vs 6 ± 2 mg/dL (P = .01); and for serum triglyceride levels, –24 ± 6 vs –5 ± 2 mg/dL (P = .01).

Compared with the control group, the soy protein group also had greater decreases in serum CRP levels (1.31 ± 0.6 vs 0.33 ± 0.1 mg/L; P = .02) and significant reductions in proteinuria (–0.15 ± 0.03 vs 0.02 ± 0.01 g/day;P = .001) and urinary creatinine levels (–1.5 ± 0.9 vs 0.6 ± 0.3 mg/dL; P = .01).

Limitations of the study include evaluation of only CRP rather than other inflammatory markers, evaluation of only a single dosage range and formulation of soy protein, lack of data on the effects of soy protein according to estrogen receptor genotype, and measurement of urinary urea nitrogen and urinary creatinine as concentrations rather than as 24-hour excretions.

"Longitudinal soy protein consumption significantly affected cardiovascular risk factors and kidney-related biomarkers among type 2 diabetic patients with nephropathy," the study authors write. "As diabetic nephropathy is a progressive disease, we expected that the conditions of these patients would have gotten worse after 4 years, but because of medical and dietary control, their conditions improved in some respects."
Practice Pearls

• Small trial of a soy-based and vegetable-based protein diet among patients with diabetes and nephropathy demonstrated that this diet could reduce levels of total cholesterol, triglycerides, and LDL cholesterol and decrease proteinuria in the short term.
• The current study finds that a soy protein diet can reduce levels of fasting plasma glucose, cholesterol, and CRP and decrease proteinuria vs a control diet among patients with type 2 diabetes and nephropathy. However, body weight was similar between the 2 groups.

Diabetes Care.  April, 2008;31:648-654.