The Fasting-Mimicking Diet (FMD) was developed by Valter Longo, director of the Longevity Institute at USC, through decades of research on caloric restriction, autophagy, and stem cell regeneration.
The key insight from Longo’s lab was that it’s not zero calories that matter — it’s the absence of signals that tell the body nutrients are available (primarily protein and sugar). With the right macro composition (very low protein, very low sugar, higher healthy fat), the body enters a fasting-like state even with some caloric intake.
The FMD human protocol is typically 700–1,100 kcal daily calorie intake.
Valter Longo describes FMD in his book The Longevity Diet: Discover the New Science Behind Stem Cell Activation and Regeneration to Slow Aging, Fight Disease, and Optimize Weight. The FMD research — including the comparison to water fasting effects — is described primarily in Chapters 6 and 7, where Longo walks through the clinical trials and the mechanistic reasoning behind why caloric restriction with the right macros mimics prolonged fasting at the cellular level.
The landmark peer-reviewed paper behind the book:
Brandhorst S. et al., “A Periodic Diet that Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance, and Healthspan,” Cell Metabolism, 2015.
How the app uses FMD: the app includes a toggle to track time spent within a fast-mimicking window. This is informational only — unlike dry fasting, enabling FMD doesn’t change your effective fast hours. Use the FMD toggle if you’ve consumed some calories but believe you’re still within FMD constraints (under 800–1,100 kcal depending on the day, with macronutrients consistent with the FMD protocol).