re: Biology, Chemist and Biochemist OTers: Help me understand weight loss.

My understanding isn't necessarily that you will burn glucose first. It is just an "easier" source of fuel. It can be broken down into energy more quickly. Therefore, at higher rates of physical exertion, you will burn glucose energy stores. When you run low, you get that bonked/drained feeling and you have no more fuel in the tank (fat can't break down fast enough to supply the energy). At lower rates of energy exertion, your body can run on fat energy stores. It's all about your heart rate and metabolic zone.

This is where people see that "fat burning zone" on the treadmill and think they need to work out in that zone to burn their fat. That's not necessarily a truthful idea. You don't lose weight 'better' just because you burned fat in that zone. You are just utilizing that as a source of energy at that level of physical exertion. In the end, you burned X amount of calories. If you burned X amount of calories in the "glucose burning zone" you'd have done the same amount of good in terms of weight loss. The source of energy just becomes more important in endurance sports like running a marathon or something.

I don't claim to be an expert. My input is about as good as any other bro-science out there. Just from a different perspective when researching running/triathlon nutrition.