FGF21 and hypogonadism: FGF21, a hepatokine induced upon fasting, exerts multiple effects such as increased ketogenesis, reduced growth as well as torpor, collectively reflecting energy-preserving mechanisms characteristic of dormancy programs.96–98 Moreover, FGF21 is a causal driver of starvation-induced hypogonadism, further underpinning its role as a mediator of such responses.99 Of note, additional functions of FGF21 in mammalian physiology have also been described.