In fact, like any good, flexible transit system, our metabolic pathways are evolved to respond to traffic conditions and send molecules to their most sensible destinations.* Got more sugars than you need? Send the extra glucose and fructose to glycogen. Glycogen stores full? Send the excess sugar to acetyl CoA. If the Krebs cycle train is overcrowded because energy demands are low, start sending acetyl CoA to fat. And there’s always plenty of space available in fat. Glycogen stores fill up, and you can’t store excess protein, but there’s no limit to how much fat you can layer on.
