Both C57BL/6J and C57BL/6N are prone to DIO, which is manifested by a marked increase in body mass (24, 27, 28), impaired glucose tolerance (27–29), an increase in fasting blood glucose and serum insulin that develops later in C57BL/6J than C57BL/6N (28), decreased insulin release (29), and insulin resistance (24). This evidence concerns the gene INS and Impaired glucose tolerance.