Inducing a three-week, HFD, protein free diet (0% of TEI) in obesity prone CD rats triggered hypophagia, increased energy expenditure, insulin sensitivity, thermogenic and FGF21 gene expression levels in muscle and brown adipose tissue; and decreased body weight, fat and lean mass compared to control rats with 15% of TEI protein intake [81]. The gene discussed is INS; the disease is obesity due to melanocortin 4 receptor deficiency.