I am sure fasting proponents promise way too many things, but the underlying cell cleanup mechanism [0] is very real and received the Nobel Prize in 2016 [1]
> fasting and CR [calorie restriction] are the most potent non-genetic autophagy stimulators, and lack the undesirable side effects associated with alternative interventions.
> We conclude that both fasting and CR have a role in the upregulation of autophagy, the evidence overwhelmingly suggesting that autophagy is induced in a wide variety of tissues and organs in response to food deprivation