Cod and soy proteins compared with casein improve glucose tolerance and insulin sensitivity in rats

The aim of the present study was to determine the effects of feeding variou s dietary proteins on insulin sensitivity and glucose tolerance in rats. Ma le Wistar rats were fed for 28 days with isoenergetic diets containing eith er casein, soy protein, or cod protein. Cod protein-fed and soy protein-fed rats had lower fasting plasma glucose and insulin concentrations compared with casein-fed animals. After intravenous glucose bolus, cod protein- and soy protein-fed rats induced lower incremental areas under glucose curves c ompared with casein-fed animals. Improved peripheral insulin sensitivity wa s confirmed by higher glucose disposal rates in cod protein- and soy protei n-fed rats (15.2 +/- 0.3 and 13.9 +/- 0.6 mg.kg(-1).min(-1), respectively) compared with casein-fed animals (6.5 +/- 0.7 mg.kg(-1).min(-1), P < 0.05). Moreover, test meal experiments revealed that, in the postprandial state, the lower plasma insulin concentrations in cod protein- and soy protein-fed animals could be also due to decreased pancreatic insulin release and incr eased hepatic insulin removal. In conclusion, the metabolic responses to th ree common dietary proteins indicate that cod and soy proteins, when compar ed with casein, improve fasting glucose tolerance and peripheral insulin se nsitivity in rats.