Originally Posted by
wolfchild
I know that glucose is a preferred fuel for the brain and body but we also have the ability to use fat as a fuel source...So why does a human body bonk and shut down when it runs out of glycogen ?... Most people have enough fat reserves to provide energy for a few days, so why doesn't human body just switch over to fat as a fuel source, so at least the person can function and continue at a slower pace ?
That's a good question. We'll have to interrogate our DNA. Why would the current system be selected for?
My guess is that carbs have always been the preferred fuel source. Fruit and shoots, right? Fat was selected as the fall-back fuel because it doesn't have the performance that carbs have. We're not supposed to bonk. I think that's an artificial state induced by modern athletic competition. Experienced randonneurs don't bonk, for instance, because they know how to titrate their resources. I think any experienced spear-and-shield hunter would do the same.
In the wild, our predators were/are sprint hunters and they can out-sprint us. We're not sprint hunters, we're endurance hunters. In theory, we can run down antelopes, although modern marathoners haven't quite been able to document this. OTOH, traditional African hunters do OK. What I'm tying to say I guess is that I can't think of a predator that would cause us to bonk and thus get eaten. I also can't think of a tribal warfare scenario where the opposing sides tried to run each other to death. Bonking a modern artifact.