There is absolutely no biological reason whatsoever for thinking that the alterations that KBLB has done to a couple of genes (out of tens of thousands!)is going to significantly alter the worms nutritional requirements.
It would take a very marked change in the overall balance of amino acids to do that, far more that would be caused by a change in one or two genes. (and the balance of amino acids in both spider and silk proteins is very similar anyway, for pretty obvious reasons.)