Since it is known that B6 mice with diet-induced obesity develop resistance to peripheral leptin, as evidenced by the effects on food intake [34] and the high gainers in our experiment indeed have higher leptin levels than low gainers, the changes in food intake and feeding efficiency that follow the early differences in body weight could in part reflect the effects of leptin resistance. This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.