According to SCD, they feel that in regards to bifidus, The problem comes in when the balance of flora is off and certain types become overly prevalent, triggering an immune response. Bifidus is one of the strains that tends to become overpopulated in an IBD-affected gut, so it's generally contraindicated within the context of SCD.
One woman told me:
"I understand GAPS's reasoning on why adding more strains like bifidus is good and that a NORMAL gut has many kinds of good bacteria in there, but the problem is, WE have got bad ones that have overgrown. And bifidus, for one, is one that tends to overgrow pretty easily. I stick to SCD on this one. I think it's safer. One can "graduate" later to more strains. And that's the point of yogurt, and/or ferments, THEY have a lot of strains in them."