Meek One said:
OP here. Got a quick question. If I do a longish L2 or L3, but suck down a couple bottles of 'energy' drink, am I burning much fat at all or simply the simple sugars I am ingesting follwed by the glycogen/fat mix...
You'll be burning quite a bit of fat at an L2/L3 pace.
As someone else pointed out you've really got to consider overall calories per day, not the specific breakdown of energy sources during your workouts.
Look at it this way, in addition to your riding you burn calories during your daily activities and burn calories simply to stay alive. There's a lot of ways to tally your baseline energy needs like BMR, RMR, etc. but the point is you'll have to find the calories to just get through the day in addition to your workouts. And most of the day you'll be at an intensity level that mostly burns fat.
So let's say your RMR or RMR plus typical non athletic daily activities requires 2000 Calories. You add a 2000 Calorie workout session on top of that for a total of say 4000 Calories burned over 24 hours. Let's say you replace 3500 of those Calories througout the day including what you eat and drink while working out. You'll be running a net 500 Calorie per day deficit. Where do you think your body finds those extra 500 Calories beyond what you've ingested that it needs to get through the day? Yeah, it comes from our abundant fat stores. IOW, as long as you maintain a caloric deficit over the long haul your body will have to mine its fat reserves to keep you going.
Maintain that 500 Calorie deficit for a full week and you'll burn a pound of fat. You won't burn a pound of carbs and unless you seriously starve yourself and neglect to keep your glycogen topped up you won't burn a pound of protein. You just don't have those kind of reserves stored anywhere in your body, but you've got plenty of fat to burn (no insult, we all do) and that's the body's preferred fuel source during those 20 plus hours when you're not out exercising.
Keep an eye on the big picture, fuel yourself before, during and after your workouts so you can keep doing them throughout the week and focus on overall daily caloric balance to lose weight which includes "fork control" as someone pointed out.
Good luck,
-Dave