Effects of Long‐Term Soy vs Casein Protein Intake and Obesity on Serum Insulin‐Like Growth Factor 1 (IGF‐1) and IGFBP‐3 Levels using Obese Female Zucker Rat Model.

Abstract

Elevated serum IGF‐1 is an increased risk for breast cancer development. The main objective of this study was to investigate the effects of high‐isoflavone soy protein diet (hi‐isof soy) and obesity on serum IGF‐1 and binding proteins (BP) IGFBP‐3 levels. Lean (n= 54) and obese female (n= 45) rats were maintained on either casein or hi‐isof soy protein diet for 155 days. All rats were orally gavaged at age 50 days with 65 mg/kg DMBA. Rats were weighed once a week and were killed 155 days post‐DMBA treatment. Blood was drawn at different ages (43, 99 and 197 d) to measure serum IGF‐1 and IGFBP‐3 by ELISA. Obese soy‐fed rats gained significantly (P<0.001) more weight than obese casein rats. At age 43 d, no differences were found on serum IGF‐1 levels among the groups but IGFBP‐3 was increased by hi‐isof soy diet in lean group compared to casein fed lean rats. At the age 99 d, obesity increased (P<0.05) serum IGF‐1 for both casein and high‐isof soy diet compared to the lean group and this increase was maintained for the rest of the experiment. At age 99 d ,obesity increased IGFBP‐3 levels in the casein but not hi‐isof soy diet group (P<0.001). At end of the Exp. (197 d); obesity increased IGFBP‐3 (P<0.05) both in casein and soy fed rats. Our results suggest that dietary protein source can affect serum IGF‐1 and IGFBP‐3 in obese female Zucker rats (Supported by USDA and ABI to RH).