Effects of Two-Month Consumption of 30 g a Day of Soy Protein Isolate or Skimmed Curd Protein on Blood Lipid Concentration in Russian Adults with Hyperlipidemia

Recently the American Heart Association has reported that favorable effects of soy protein on blood lipids were characteristic only for high amounts of soy protein and not observed for an intake less than 30 g/d. However, the period of the studies with the smaller amount was 4-6 wk and we thought a longer study was necessary for the conclusion. The death rate by heart disease is very high in Russia; therefore, we have done this study in Russian subjects with hyperlipidemia. Prior to the study we tried to find a favorable method for subjects to take 30 g protein a day from soybean protein isolate (SPI) or skimmed curd protein (SMP) and decided to use Russian style cookies. Thirty subjects with hyperlipidemia were recruited; however, due to the 5-mo long study 28 of them (19 females and 9 males aged 50+/-2 y) could complete the trial. They were randomly assigned to two groups and were given either cookie for 2 mo separated by a month-long washout interval in a cross-over design. Fasting blood samples were drawn before and after the dietary treatments. Fasting blood samples at 1 mo were also measured as a health check and to observe the trends of the blood parameters in the middle of the study period. Serum samples were used for the lipid and other biochemical measurements. Every month for 3 non-consecutive days, energy and nutrient intakes were assessed and physical activity was estimated by pedometer. With the consumption of SPI for 2 mo, concentrations of total-cholesterol changed from 280+/-7 to 263+/-8 mg/dL (-6.5%, p=0.0099), HDL-cholesterol from 57.4+/-2.5 to 62.6+/-2.9 mg/dL (+9%, p=0.0047), non-HDL-cholesterol (total-cholesterol-HDL-cholesterol) from 223+/-7 to 201+/-8 mg/dL (-11%, p=0.0023) and triglycerides from 204+/-23 to 173+/- 19 mg/dL (-18%, p=0.022). There were no significant changes with SMP (p>0.05). Thus, administration of 30 g SPI a day for 2 mo confirmed its favorable effects on serum lipids in Russians with hyperlipidemia.