In this episode of humanOS Radio, Dan speaks with Javier Gonzalez. Dr. Gonzalez is a professor at the Department for Health at the University of Bath in the UK. He and his colleagues recently published a hypothesis suggesting that carbohydrate availability plays a key role in the regulation of energy balance, and explains both why exercise increases hunger and (paradoxically) why people who are highly active exhibit better appetite regulation. What do I mean by carbohydrate availability? Well, our storage capacity for carbohydrates is relatively minuscule, compared to fat stores - even on a very lean individual. These stored carbs can be depleted much faster, and several studies suggest that alterations in carbohydrate availability may be carefully monitored by the body. Importantly, physical activity alters carbohydrate availability by expending muscle glycogen. This may be why exercise has been shown to acutely lower fasting leptin concentrations. Reductions in carbohydrate availability resulting in a drop in leptin levels may explain, for instance, why individuals who utilize carbs faster during exercise seem to be more prone to increased appetite after exercise. But high physical activity levels - and accompanying high physical fitness - produces relevant changes in carbohydrate and fat metabolism, that might actually make them better able to rein in their appetite after a bout of exercise or after a larger-than-normal meal. To learn about these changes, and more about his fascinating hypothesis, check out the podcast!