With respect on how to fuel your body BEFORE workouts things are, once again, controversial.

(I say go with the balanced diet thing and figure out how much time is optimal for you between meal and workout. You don't want to feel starving during working out (that would be the feeling of your body catabolizing / eating your hard earned muscle) but you don't want to feel bloated either. I workout early in the morning and a banana, small handful of peanuts, and cup of milo 20 minutes prior work for me.)

Your body can use different sources of fuel.

ATP / glycogen is stored in muscles and this is your bodies first choice of a fuel source. Since it is actually stored in the muscles it can be accessed quickly. It is most useful for things such as fast sprints / strength based weight training / maximal effort kinda stuff. The source of this is sugar / carbohydrates (so the idea of 'energy drinks' helping replenish this source). This source runs out quickly, though. That is why they say to not strength train for more than about 40 minutes or so.

Fat stores are a backup. Runners experience this 'wall' kind of block when the body is running out of the first source just before it switches to the second. This second source requires oxygen for metabolism (which is why my smoking impacts on cardio more than strength). This second source isn't as good at fast / explosive but can be sustained for much longer periods of time (e.g., marathons).

(A third source is your body catabolozing / eating your muscle mass)

So, while there are these two sources of energy the thing is that in practice your body uses a little from both, it is just that the ratio is different for different kinds of activity (e.g., strength is mostly the first, steady state cardio is mostly the second).

There was a study done where it was found that when peoples heart rate was within a certain range the ratio of fat to glycogen burning was much higher than when their heart rate was higher than the range or lower than the range. This range was dubbed the 'fat burning zone'.

As a result of this many people attempt to do 'steady state cardio' keeping their heart rate within the fat burning zone. Takes about 20 minutes for the glycogen stores to deplete and then the thought is that you are working most optimally for fat burning.

PROBLEM:

lets say that the fat burning zone yields a 60-40 ratio of fat burning to glygocen burning (at least until glycogen runs out).

lets say that working within the fat burning zone burns 100 calories per hour.

lets say that working above the fat burning zone yields a 50-50 ratio of fat burning to glycogen burning.

lets say that working above the fat burning zone burns 200 calories per hour.

Exercise for you: Which workout burns the most fat?

(ANSWER: Fat burning zone workout burns 60 fat calories per hour. Working above the fat burning zone burns 100 fat calories per hour. Once glycogen stores are depleated fat burning zone workout burns 100 fat calories per hour. Once glycogen stores are depleated working above the fat burning zone burns 200 fat calories per hour. Working above the fat burning zone burns more TOTAL calories from fat even though the RATIO of calories from fat is lower than the RATIO of calories from glycogen).

High Intensity Interval Training (periods of almost maximal effort then periods of backing off) in conjunction with Strength Training provides the best way to burn fat stores and build lean muscle mass. 20-40 minutes Interval Training 3x a week (depending on the intensity) in addition to Strength Training is most effective. Of course one needs to build good aerobic capacities in order to do the 'high intensity' stuff, but aiming for 'high intensity interval training' is the most useful thing to do with cardio if one wants to burn maximal calories from fat.

Consuming simple carbs before working out (or during working out) will help replenish your glycogen stores for an 'energy burst'. It will also result in less fat being burned, however. Some people swear by aerobic first thing in the morning before food consumption. That is because they are trying to deplete their glycogen stores by starvation. Working out while weak isn't such a good idea (one is more prone to injury). Also... If you do care about promoting lean muscle mass (having the energy to lift hard and workout above the fat burning zone to becoming a strong and healthy woman) rather than promoting skinniness (endless steady state cardio where your body eats your muscles rather than relinquishing those fat stores) then you don't want to be working out before fueling your body! If you don't eat regularly (at least 5 times a day) your body will catabolize muscle for energy rather than utilizing fat stores (once you get to a certain body composition at any rate). It needs to be able to depend on a regular calorie intake.

(Your fatigue might be because you actually need to be eating more calories now. I'm eating much more than I used to even though I'm still losing fat and my weight is remaining pretty constant)

:-)