Dietary β-Conglycinin Modulates Insulin Sensitivity, Body Fat Mass, and Lipid Metabolism in Obese Otsuka Long-Evans Tokushima Fatty (OLETF) Rats.

The physiological effects of dietary beta-conglycinin (beta-CON), one of the major components of soy protein (SOY), were examined in an obese animal model. Prior studies show that beta-CON intake decreases plasma triglycerides and visceral adipose tissue weight, and increases plasma adiponectin in rodents. Since plasma adiponectin is known to affect both lipid and glucose metabolism, feeding a diet containing beta-CON could modulate insulin sensitivity. Therefore, we examined the effects of dietary beta-CON on insulin sensitivity and blood glucose levels, as well as lipid metabolism in obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats (pre-symptomatic stage of type 2 diabetes mellitus). Male OLETF rats (6 weeks old) were fed diets containing 20% protein such as casein (CAS), CAS replaced with soy protein (SOY), or beta-CON at a proportion of 50% for 13 weeks. Fasting blood glucose levels were measured every 3 weeks, and an insulin tolerance test (ITT; 0.75 IU/kg body weight) was conducted at week 12. During the feeding period, fasting blood glucose was comparable among the groups. Insulin sensitivity measured by the ITT revealed that the SOY and beta-CON diets decreased blood glucose levels at 30 min after intraperitoneal insulin injection (vs. CAS diet). In addition, the beta-CON diet increased plasma adiponectin concentrations, hepatic gene expression of insulin receptor substrate (IRS) 2, and muscle gene expression of adiponectin receptor 1 (AdipoRl) and IRS1, and with a decrease in plasma insulin concentration. Finally, the beta-CON diet decreased the mesenteric adipose tissue weight and liver triglyceride concentration compared to the CAS diet. These results suggest that the metabolic effects of dietary beta-CON are mediated by increasing plasma adiponectin to increase insulin sensitivity and influence the hepatic lipid metabolism in obese OLETF rats.