Meat, eggs and cheese have virtually no carbohydrates. Cow's milk does have some carbohydrate. Where as plant foods, especially sweet or starchy foods, are abundant in carbohydrates, and it is readily useable. Fruit is the best source of quick carbohydrates. They are quickly digested and the carbohydrate is in an easily assimilate able form.
Fruit is the perfect fast food for the athlete.
You also see fruits such as sliced oranges and firm melons being given to athletes during breaks. When I played varsity school sports, I can always remember sliced oranges. I can never recall, cow's milk, chess, meat or eggs. Breads, pastas, potatoes, rice, sprouted or cooked grains are all great carbo loading foods. The fibre in the whole grains help slow the release of carbohydrates over a period of time, thus sustaining the energy flow longer.