Letters to the Editor

insulin resistance Dear Sir: I read with interest the article by Domouzoglou and Maratos-Flier (1), which summarizes current knowledge on fibroblast growth hor-mone 21 (FGF21) and provides insights into the potentially promising applications of this endocrine factor in the treatment of nonalcoholic fatty liver disease, obesity, and type 2 diabetes. Studies in mice fed a ketogenic diet greatly contributed to the understanding of the phys-iologic roles of FGF21. Domouzoglou and Maratos-Flier emphasize that ketogenic diets lead to weight loss and improvement in insulin sensitivity (1). Al-though I agree with the effect on body weight, I am more skeptical about the effect of ketogenic diets on insulin sensitivity. Indeed, using the hyperinsulinemic-euglycemic clamp technique, which is the gold standard to assess insulin sensitivity, we recently showed that mic