The present invention provides a non-human mammal deficient in the expression of the SLC-1 gene, having the characteristics of (1) a lower blood insulin level in glucose tolerance test, (2) increased insulin sensitivity, (3) higher resistance to obesity even on high fat diet, (4) a smaller white fat cell size, and (5) accentuated lipolysis, compared with the corresponding wild-type animal, or a portion of the body thereof. Also provided is an obesity and/or type II diabetes model non-human mammal that is deficient in the expression of the SLC-1 gene, having the characteristics of (1) elevated expression of adiponectin, (2) delayed onset of hyperglycemia, (3) a lower blood glycohemoglobin level, and (4) accentuated energy consumption, compared with the corresponding obesity and/or type II diabetes model non-human mammal wherein the expression of the gene is normal, or a portion of the body thereof.