Calories - how many?

If you don't eat enough, you'll loose weight (hopefully body fat). If your weight is stable then you are eating enough.

However, for optimal performance, an adequate supply of carbohydrates is required. For most club cyclists on say 9 to 12 hours per week, you'll require about 6 to 8 g/kg body mass per day of carbohydrates, and 1 to 1.5 g/kg body mass per day of protein.

During actual exercise, you'll need 0.5 to 1g/kg body mass of carb per hour depending on the intensity of exercise, environmental conditions and fluid and electrolyte intake.

The actual amount of energy that you expend will be dependent upon your training volume and intensity and your efficiency (which changes at different intensities and under different conditions). You can get a good ballpark figure for energy expenditure during cycling exercise by using a power meter (Power Tap or SRM only) and looking at the total kj expended, and just transposing that figure to kcal (due to an approximate cancellation of 4.18 kj to kcal and the body being ~ 20 - 25 % efficient), i.e., if you expend 1500 kj on a bike ride, that's about the same as 1500 kcal. You can only find the exact expenditure by going to an exercise physiology lab, but efficiency changes at different intensities!

Ric