This is something that I read about every single day, whether its PT's talking about carbs, or the general public. Do carbs make actually make you fat though? No, and here's why.
I have been injured for a total time of about 14 weeks, but I did 'come back' for a couple of weeks in the middle. During that time where I was unable to workout, I still ate carbs, every day, and I can honestly say that I have not gained 'fat'. I have lost muscle size and tone, so it looks like I have gained fat, but its purely because the shape and definition is no longer there. The carbs that I have eaten have been potatoes, rice, couscous and pasta. So, to those people that say carbs make you fat, why haven't I gained any fat? considering I haven't been able to workout at all for quite a long time, if they caused weight gain, surely I would have experienced that?
The thing that causes weight gain is you. If you eat too many carbs, and do no exercise, yes you will gain weight as the carbs will turn into stored energy, rather than being used. So if you choose to eat too much, then you will get fat, but carbs themselves do not instantly add fat. Its all about moderation - you want to eat a variety of foods, but not too much.
By going on a 'no carb' diet, then you are doomed to fail. Your body needs energy to function, and carbs are its primary energy source. Is it possible to never eat carbs again? hell no. I always say - if you can't do it forever, don't do it at all. Don't be afraid of carbs, your body needs them, but just don't eat too much.