In The Fourth Fuel, science writer Travis Christofferson weaves a fascinating narrative of humanities quest to understand how our bodies produce energy—transporting us on a scientific expedition from the past to the present—across early modern Europe to modern laboratories spanning the globe. The reader is taken on a riveting and revelatory journey that follows Nobel Prize-winning scientists from the 19th and 20th centuries as they map the pathways and cycles that comprise human metabolism. The reader is left with a new and lasting appreciation for the silent chemical motion that keeps us alive and healthy. Ultimately, the narrative arrives at a remarkable discovery that rewrites everything we thought we knew about metabolism—with profound therapeutic consequences. Coming back to the present, Christofferson reminds us that Americans are sicker than they have ever been. Heart disease, cancer, dementia, obesity and type 2 diabetes are rapidly becoming the norm. Yet we are presented with a revelation: the realization that we all have a potent, and easy-to-access hybrid metabolism that generates a different fuel—the fourth fuel—that “supercharges” our metabolism in a way that slows aging and by-passes the metabolic dysfunction that leads to the multitude of diseases that plague modern society.