Since calcidiol is the vitamin D metabolite that best reflects nutritional intake23, the origin of the decreased plasma calcitriol in rats fed HF diets cannot be attributed to decreased dietary intake of vitamin D. The most likely explanation for the decreased calcitriol is a reduction in calcitriol synthesis secondary to the increase in FGF23, which is known to inhibit the 1-alpha-hydroxylase activity in the kidney24. The gene discussed is FGF23; the disease is hydrops fetalis.