For me, riding means mostly 1.5 to 2 hour hard rides. I rarely drink anything but water but near 2 hrs. I do feel the lack of energy. This would match Silver’s data well. If it’s hot and I know I’m riding 30+ miles I’ll mix an energy drink with water. I totally agree protein has little to do with short term energy use. On Centuries etc. I eat a bagel, nanner or 2 and I’m good to go.
References :

Now, a few things on fueling and energy

1. You normally have around 2000 calories worth of glycogen stored in your muscles and liver. That should be enough to carry you through any races or workouts up to maybe 2 hours. If you are on a longer ride or race, you should start supplementing calories at 60-90 minutes. Depleting your glycogen (carbohydrate) reserves is known as Bonk. Your legs go dead, and speed drops drastically in a matter of minutes. Short of eating, there’s nothing you can do about it. I use Cytomax, Gatorade, and Powergel during races, because they don’t challenge my digestive tract. On long non-competitive rides or runs, I might add solids like Powerbars, Clif Bars or whatevers available. Everyone’s digestive tract is a little bit different, so you have to figure that out for yourself what works best.

2. The primary reason for the sugars in Gatorade is to speed fluid absorption. A 7% carbohydrate solution gets through the intestinal wall faster than water (or any other concentration). The supplemental calories are useful on long efforts to be sure, but that wasn’t the original purpose back at U of F.

3. Note to Inkncraig: protein is a bit player in energy production. See links below. Yes, the data is real. I was one of the test subjects in some of the studies.

4. Long distance fueling: Bars are mostly a convenience item. A banana or a bagel is probably as effective, but they don’t always travel well in a jersey pocket. The other part of it is your ability to digest and absorb at higher heart rates. On a charity ride, you’re not going that hard, so keeping up with fuel requirements isn’t difficult. At race pace, ie, around AT consensus is that most people can’t absorb more than 275-300 kcal per hour. Excess is either ejected, or sits sloshing in the gut. Races like Ironman are often decided by fuel management rather than aerobic capacity. Whoever best balances heart rate and fuel reserves vs. fluid and calorie intake comes home first.
References :
http://www.gssiweb.com/Article_Detail.aspx?articleid=719&level=2&topic=8

http://www.gssiweb.com/Article_Detail.aspx?articleid=32&level=2&topic=8

It’s important to load up on complex carbs like rice, pasta, or potatoes within an hour after finishing a training session or they won’t be properly resupplied to your muscles, and to eat a load of protein within two hours of finishing a session. If you do this you’ll be good to go within another two days.
References :

HTH
References :