Will exercise and improved fitness make you a better trader? Difficult one that. I would suggest exercise and improving your physical fitness makes you feel better physically and also mentally. If you feel better mentally, your psychological disposition when trading must also improve, even if it's only feeling less wretched on a losing run.
I think being in at least decent physical condition will definitely help. Better circulation, better flow of oxygen to the brain, more focus.
Also definitely agree with the points about drinking plenty of water and eating sensibly. That said, though, I do wonder if trading very slightly tipsy to take the edge off nerves might work well...