i think that there is a waiting period where your body is shifting from burning carbs to burning fat. sometimes it's best to wait AT LEAST a week before starting the exercise. it takes a few days to make the switch and a good ten days to really switch the body over. so, you are not yet burning fat for energy but you are also not giving your body any of the carbs it's conditioned to burn. you are actually relying on protein a bit as a glucose source (gluconeogenisis) That's why you feel wiped out. less is WAY more in this case. so, wait a week and then when you feel the energy kick in (the switch) then try to slowly incorporate exercise again. i think everyone is different. i know this is what i needed to do to. take care.....