Peter Attia was one of the biggest proponents of fasting, and did regular TRF along with periodic multi-day water-only fasts, but stopped completely after his DEXA scans showed drastic muscle loss, even with regular strength training. Multiple studies have shown that when used as a weight loss tool, it's no better than regular caloric restrictions, and that it actually results in worse body composition, skewing the weight loss towards muscle and away from fat: https://jamanetwork.com/journals/jamainternalmedicine/fullar...
>In this RCT, a prescription of TRE did not result in weight loss when compared with a control prescription of 3 meals per day. Time-restricted eating did not change any relevant metabolic markers. Finally, there was a decrease in ALM in the TRE group compared with CMT. Together, the results of this study (1) do not support the efficacy of TRE for weight loss, (2) highlight the importance of control interventions, and (3) offer caution about the potential effects of TRE on ALM. Future studies should be aimed at understanding the effects of early vs late TRE and protein intake or timing as a means to offset the loss in ALM.
ALM = Appendicular (i.e., limb) Lean Mass.