The majority of literature surrounding energy gels or goos tends to be regarding which brand or flavor to use, and at what point of training to ingest them. The real question is are they needed?
The whole idea of ingesting one of these supplements is to obtain energy through the source of glucose or carbohydrate. Our bodies are able to utilize its own glycogen stores for a given period of time during exercise which can be up to 2 hours before it starts to run out and become dependent on external sources or muscle. This is the point commonly referred to as bonking.
The key to endurance training in preparation for a marathon is to teach the body to become efficient and not rely on supplementation. In other words burn fat instead of glycogen. During base training and on long slow runs, if we train at an aerobic rate (slower rate which avoids lactate threshold) we train our body to utilize fat for energy. Fat storage in the body is pretty much unlimited and can sustain a runner through an entire 18-20 mile run during training periods. When training with energy gels, the body becomes dependent on this external synthetic source of energy reducing its ability to become efficient. Instead of running harder and ingesting energy gels during a training run, slow down and become efficient at burning fat.
What about during a race? The philosophy differs as we are now pushing our body and will be utilizing more glycogen. If it takes us longer then 2 hours to complete a marathon (which is pretty much most of us!) then using energy gels or goos as a supplementation can help. Fat will still be the primary source of fuel during a marathon, but given that it is a race and we are pushing the limits we will utilize glycogen. If we start the race too hard and utilize all of our glycogen, then the second half will become very challenging forcing the body to slow down. If we conserve however, and rely on our fat burning more efficient engine, as we enter the second half (and even more so the last 6.2) we will have enough glycogen at hand to finish stronger. For an energy gel to be useful it should probably be consumed closer toward the end of the race to put some extra glucose on hand for the last several miles when you may want to pick it up.
If you are used to training with energy gels on long runs and become hungry when trying to run without them, you are most likely training too hard and depleting your glycogen stores instead of burning fat. Slowing down on your long runs will certainly help this. Also, eating a banana, a bagel, or drinking a glass of juice can be enough to reduce the “empty stomach” feeling that is present if you run in the AM. Remember, what we have eaten the week leading up to a long run is far more important then “carb loading” the night before.
So don’t expect to get faster by swallowing several gels down to get added energy. Speed will come from an efficiently built engine.