Vivian - I do P90X on under 100g no problem (in fact usually under 50g). I feel better at this level than when I was eating 200+ carbs and having recovery drinks etc. Now I just eat straight after and have no problems. I actually find my muscles are less sore on low carbs and all the niggling litte aches have also pretty much gone (i used to get sore toe joints and thought it was early arthritis but now I realise it was probably the grains). Just take it easy in the early days, go at your own pace and and 'press pause' if you need to.