“The fasting mimicking diet regenerates the immune system”

## The Evidence Longo et al. (2014, *Cell Stem Cell*) showed in mice that 3 cycles of prolonged fasting (48–120 hours) reduced white blood cell counts followed by stem cell activation and immune regeneration upon refeeding. In a small human pilot (n=3 chemotherapy patients), the same pattern was observed. A follow-up 2016 paper tested the FMD (fasting-mimicking diet, 800–1,100 kcal/day for 5 days, 4 cycles) in 100 participants and showed reductions in risk factors for aging, diabetes, cardiovascular disease, and cancer — with one arm showing regenerative markers. ## The Limitations The human immune regeneration finding comes from 3 participants — essentially a case series. The FMD RCT is larger but uses biomarker endpoints, not disease outcomes. These findings are highly promising and mechanistically coherent (IGF-1 suppression reduces PKA signalling, promoting stem cell self-renewal), but the "regenerates the immune system" claim is far stronger than the human evidence base supports.