Lots of people told me i couldnt do exercise if i wasnt eating carbs. But apart from first two weeks i have had tons of energy and regularly do two intensive dance sessions a day. I am very careful to eat both before and after plus plenty of water.
Dh really struggled at the gym first month or two - we decided it was low blood pressure and he wasnt drinking enof water in the run up to exercise ( not during). Also he forgets to eat regularly!
All depends how your body works of course - but figure that out not what internet says
good luck
Xx