The only time I had trouble working out was when I tried the fat fast for two days. I learned my lesson, felt awful. On less then 20 g I get plenty of energy from protien and snacking, and by drinking a ton of water I don't have the leg cramp problem.

I do water arobics, weight lifting, yoga and want to start pilates (yes that sounds like alot, but I don't do them all on same day, and sometimes I forget to exercise for a day or two. Variation keeps things interesting.)