TLDR - Alternate day fasting leads to hair follicle damage in mice.

• Common intermittent fasting regimens inhibit hair follicle regeneration in mice
• Fasting selectively eliminates activated HFSCs, but not EpiSCs that maintain epidermis
• Activated adrenal gland-dermal adipocyte crosstalk mediates HFSC apoptosis
• Intermittent fasting inhibits human hair growth in a randomized clinical trial

https://www.cell.com/cell/abstract/S0092-8674(24)01311-4

Nick Norwitz did a great writeup https://staycuriousmetabolism.substack.com/p/fasting-will-make-you-bald-and-how

I haven't found the full paper in the usual places. So I'm relying on the writeup

In both mice and humans topical vitamin E proved to provide enough antioxidant protection to prevent the hair loss.