You need cards, losing them completely is just dumb. As they are the main source of your energy. So you won't have enough energy to workout.

ExCal - so true! Carbs are so imortant and no one realizes this - all because there has been so much talk about no or low carb diets being so successful.

I don't think the ultimate absence of one nutrient would do good for the body. Well for one, carbohydrate is still important in our body, remember that it keeps the body energized and restores body heat, so it would really be a bad idea if you just stop taking carbo. Maybe a little carbo would do, anything that is in moderate is good.