Mark Sisson and Brad Kearns discuss the topics of metabolic flexibility and metabolic efficiency. The conversation starts around the topic of prescriptive one-size-fits all approaches to diet and how Mark's work with primal, keto, and intermittent fasting are all different paths in pursuit of the same goal: metabolic flexibility. Mark pushes back on some current trends in the world of health and fitness regarding speeding up your metabolism, bioenergetics and the work of Ray Peat.