Diet

What you eat when you start to train will impact on your cycling and energy levels.  Initially while the training is at a low weekly mileage it would be best to concentrate on eating in a regular pattern and trying to reduce your daily intake of saturated fats.  This includes less fried foods and dairy products as these will counter any training you start to do.

As your mileage increases it would be worth trying to ensure that at least one meal a day is high in carbohydrate, this is the product that once stored in your system will give you energy.  Carbohydrate is found mainly in the form of potatoes, bread, pasta and rice and so is easy to base any meal around.  Combined with this increased intake of carbohydrate must also be a good mixture of vitamins and minerals found in fruit and vegetables.  The fruit in particular is an ideal food for cyclists because it is high in fructose which also provides cycling energy as it is more easily absorbed from the stomach for use than other sugars (such as insulin obtained through eating chocolate).  Bananas are usually the preferred energy provider for cyclists especially when needing to maintain energy out on a ride.

Meat and fish provide some essential micro-proteins which help muscle development.  If you plan to be really healthy it is best to eat fish and white meats such as chicken; if you are going to eat red meats you should cut as much fat off as possible and cook it in a healthy way such as grilling.  If you are a vegetarian this is not a major point of concern: you will have probably established a balanced diet already, so you may only find yourself looking for food stuffs that give you more energy.

There are many energy bars available on the market now such as power bars or Clif bars, which are a concentrated source of energy providing elements to help you maintain your cycling should you start to wane.  These do work but are much more expensive than bananas or other forms of fruit. 

Fluids are another area in which you will have to increase your intake as you will start to lose more from your system by sweating and other exercise related matters. This is simply combated by drinking a lot more (water, not alcohol!). You can also increase your energy levels through the intake of isotonic drinks or concentrated fruit juices, some people find these work very well and the psychological effect by itself is often enough to make them worthwhile. If you intend to use these on the challenge it is a good idea to get your body used to them while training.

Basically if you are careful with your diet, trying to eat more healthily and ensuring you eat plenty of carbohydrate before and after long rides, you will be fine.  You may well find yourself enjoying eating more as the guilt disappears because you know you have exercised!