USC researcher Valter Longo developed the Fasting Mimicking Diet (FMD), a 5-day protocol that provides fasting benefits while still eating.
Dr. Valter Longo stands at the intersection of fundamental aging biology and practical nutrition. As the director of the USC Longevity Institute and professor of gerontology at the University of Southern California, he has spent his career asking a deceptively simple question: how can we eat less while eating more? His answer—the Fasting Mimicking Diet—has transformed the conversation around fasting from an all-or-nothing proposition into something more nuanced and scientifically grounded. To understand Longo is to understand one of the most promising approaches to extending both lifespan and healthspan through manipulating the body's metabolic signals.
Longo's path to becoming a leading longevity researcher was unconventional. Growing up in Italy, he was influenced by his family's Mediterranean diet and the general longevity that seemed to characterize his region. This cultural context, combined with an early fascination with biology, led him to study biochemistry. But it wasn't until he began working in the laboratory of Roy Walford, the legendary gerontologist famous for his own caloric restriction experiments, that Longo's life's work truly crystallized. Walford had demonstrated that drastically reducing calorie intake could extend lifespan in mice and other organisms, but the mechanism remained mysterious. Longo became obsessed with understanding how caloric restriction worked at the cellular level and, crucially, whether there were ways to achieve its benefits without the suffering of continuous caloric restriction.
This research took him to the USC Longevity Institute, where he established a laboratory focused on nutrient-sensing pathways—the cellular mechanisms that detect whether nutrients are abundant or scarce and trigger corresponding adaptations in aging and metabolism. His key insight was that organisms don't respond to the total number of calories consumed as much as they respond to specific nutrients and signaling pathways. Specifically, Longo became fascinated by three interconnected pathways: mTOR, IGF-1 (insulin-like growth factor 1), and insulin signaling. These pathways represent a kind of nutrient-sensing system that tells the cell whether food is plentiful or scarce. When nutrients are abundant, these pathways activate and push the cell toward growth and reproduction. When nutrients are scarce, they quiet down and the cell shifts into maintenance and repair mode.
The fundamental theory underpinning Longo's work is that aging is fundamentally linked to these nutrient-sensing pathways running in overdrive. In modern societies with abundant food, our cells are essentially constantly "fed" at the signaling level, pushing them toward growth and away from repair. This state of constant nutrient-sensing activation accelerates aging because the cell deprioritizes the cleanup and maintenance systems—like autophagy—that keep organisms healthy. Conversely, periodic nutrient scarcity, achieved through fasting or caloric restriction, downregulates these pathways, activates cellular repair mechanisms, and may slow aging.
But Longo recognized early on that asking people to fast for extended periods or maintain chronic caloric restriction was impractical and unsustainable. Most people couldn't do it, and those who tried often developed problematic relationships with food or suffered nutritional deficiencies. So he began asking a different question: what if you could provide the fasting signal—the metabolic changes—without actually fasting? This led to the development of the Fasting Mimicking Diet, or FMD, one of the most rigorous dietary interventions in longevity research.