Reviewed September 2026. Covers the fat-loss, exercise, frequency and diet-setup chapters of both books, plus the online calculator. Added so you don't have to scroll 4b. The "fasting mimicry" claim is biochemically wrong IMO This one won't cost you muscle or fat loss. But if you bought into the idea that RFL days give you the cellular benefits of fasting, you should know the claim doesn't hold. In Chapter 11 he writes: "Fundamentally, my RFL is nothing but a ketogenic diet without the dietary fat. Which means that it generates the same basic physiological shift as with complete fasting." He's half right. RFL does deplete liver glycogen, shift you towards fat oxidation, and produce ketones. That's the metabolic switch. Fine. What it does NOT do is replicate the cellular signalling state of a true fast. The reason: he's telling you to eat 150–220 g of protein on those days. The amino acid leucine — abundant in every lean protein source he recommends — is the most potent known activator of mTORC1. And mTORC1 activation directly suppresses AMPK and shuts down autophagy (Levine & Kroemer, 2019; Alirezaei et al., 2010). Translation: the protein that protects your muscle is the same protein that prevents the cellular cleanup he's claiming you get. You cannot have both simultaneously. Does this matter practically? For his stated goals — fat loss without muscle loss, training support — no. The RFL day works brilliantly for those. But if you were banking on autophagy, mitophagy, or the hormetic stress-response benefits that the fasting literature discusses, an RFL day will not deliver them. You'd need actual amino-acid deprivation for that, which is the opposite of what he prescribes. He also dismisses Longo's Fasting Mimicking Diet as "nonsensical" while running what is functionally a modified fasting-mimicking approach himself — just with the right macronutrient (protein) instead of the wrong ones (carb/fat). The dismissal is ironic and the physiological claim needs a qualifier.