I am working on taking my certiifed personal trainer exam and one of the essay questions was about this. Here is what I answered (I used this solely from my curriculum during the course!)
"Pre-exercise nutrition can help the client maintain even levels of blood sugar and prevent early fatigue. The client should consume a low-fat, high carbohydrate diet daily. This will help maintain adequate glycogen stores in the muscles and liver. The client should avoid foods high in fat and protein before working out.
If the client is exercising less than an hour, good carbohydrate choices include bagels, plain or toasted bread, crackers, plain pasta and bananas. If the client is exercising longer than an hour, good choices are bananas, oatmeal and apples because they have a low glycemic index. Carbohydrates eaten well in advance of a workout can fuel the client’s performance as exercise intensity dictates, as a result of glycogen being stored in the muscle or liver. Foods with a low glycemic index rating eaten about an hour before a workout are digested enough to be used as fuel.
If a client wishes to eat a snack of simple sugars (such as sodas, candies and sports drinks), the client should consume these snacks about 5 to 10 minutes before exercising. If they consume these snacks less than 15 to 120 minutes before a workout, the client may experience a huge decrease in blood sugar, leaving them feeling exhausted and light-headed. By consuming these snacks 5 to 10 minutes prior to working out, the time span is probably too short to allow insulin to be secreted from the pancreas into the bloodstream and lower their blood sugar"
I haven't gotten a grade on this, but it was taken from the study materials. Hope this helps!!
Julie