A fasting-mimicking diet (FMD) is a structured, calorie-restricted protocol — usually around five consecutive days, repeated monthly or every few months — that aims to reproduce the metabolic effects of water-only fasting while still providing some food. Intake is low in calories, sugar and protein and relatively higher in healthy fats, which keeps the body in a fasting-like state (low insulin and IGF-1, raised ketones) without complete food elimination.
The approach was developed by Valter Longo and colleagues, whose studies report lower IGF-1, activation of autophagy, and markers of cellular rejuvenation in animals and early human trials. Compared with a daily pattern such as intermittent fasting, the FMD is periodic and more intense, sitting between everyday time-restricted eating and prolonged, supervised fasts.
Human evidence is still emerging, and the diet is not for everyone — people who are pregnant, underweight, diabetic, or have a history of disordered eating should avoid it, and longer or repeated cycles are best done under medical supervision. Commercial FMD kits exist, but the underlying principle is the periodic, controlled reduction of calories rather than any specific product.