CYCLING PERFORMANCE TIPS
The principles are based on nutrition and sports physiology, so it's not surprising to find similar recommendations at many websites. The summary below is based on an excellent summary by Dr. Mirkin which I have added a few comments.
Cycling doesn't require special sports drinks or power bars. Even the most elite athletes can get the nutrients they need from ordinary foods and water. Healthy and fit people generally don't need to eat during a ride of less than two hours at a casual pace. However, they can prolong their endurance for a longer rides by using snacks that contain readily available carbohydrates (sugar).
Muscles use primarily sugar and fat for energy. The harder you ride, the more the ratio shifts towards sugar as an energy source. There is an almost infinite amount of fat stored in the body, but you only enough sugar (stored in your liver and muscles) for 70 minutes of intense exercise.
To maintain blood sugar levels, your liver constantly releases sugar into the bloodstream. For normal daily activity, there is enough sugar stored in your liver to last twelve hours but with intense exercise, less than 70 minutes worth.
When your blood sugar drops, it is impossible to maintain any intense physical activity and you feel weak and tired. This is called "bonking".
An hour or more before your ride, eat oatmeal or whatever you normally eat for breakfast. Avoid high-sugar-added foods such as pancakes with syrup as they can cause a high rise in blood sugar, which leads to a high rise in insulin, and is followed by a drop in blood sugar (that will make you feel tired.) If it is not used immediately by the exercising muscle, the extra sugar you ate just gets stored as fat and does nothing to help you during your ride.
Sugar Before and During a Long, Hard Ride
Do not eat sugary bars or snacks more than five minutes before you start your ride, or wait until you are underway. Sugar eaten when and your muscles are not contracting, produces a high rise in blood sugar, the release of large amounts of insulin, and a rebound drop in blood sugar levels that leaves you feeling weak and tired.
On the other hand, exercising muscles do not need insulin to draw sugar rapidly from the bloodstream. thus keeps the levels low and avoids triggering insulin release. So taking sugar during exercise or just before you start usually does not cause the high rise (and rebound drop) in blood sugar levels.
The rule of thumb is that you should take a source of sugar during a hard ride lasting more than an hour. Use a sugared drink, jelly beans, gel packets or any other convenient source. You don't need special sports drinks or energy bars because no sugar source is more effective than one that contains glucose and fructose - and almost all types of sweet foods contain these two sugars.
If you are anticipating a longer and more intense ride, take sugar before you feel hungry. Hunger during exercise is a very late sign of not getting enough calories. By the time you feel hungry, your body will be so depleted of sugar that you will have to stop or slow down to eat carbohydrate-rich food just to restore your sugar supplies. Prevention is definitely easier than playing "catch up".
Salt and other minerals.
The only mineral that you may need during a long ride is sodium, regular table salt. Most authorities agree that you need to take in extra salt during extended athletic competitions in hot weather, but do not need to take extra potassium, magnesium or any other mineral during exercise. However, most snack foods contain enough salt to provide all you need.
Sports drinks generally contain all the salt you will need. Just take enough volume to keep your weight from dropping when you are exercising in the heat. If you think you maybe not getting enough salt on a hard ride lasting longer than three hours, snack on salty foods such as salted nuts or potato chips. Salt tablets are not necessary!
Eat Within an Hour After a Hard Ride
Eating within an hour after finishing a ride replenishes stored sugar faster than if you eat later. Within one hour after your hard ride, eat fruits, vegetables and grains (for carbohydrates) and nuts, beans or seafood (for protein), or whatever else you like. Add salt if you have been sweating a lot. Protein may both aid the absorption of sugar as well as aid in muscle healing, so make sure there is some protein in those snacks. As long as the post-ride meal contains protein and carbohydrates, it doesn't really matter what you eat.