We all know that the B vitamins work synergistically, but has anyone seen a source for the claim that taking a B complex depletes B2?
I haven't seen a source, though to me it does sound entirely plausible.
It's true that B2 is needed in the conversion of (at least some) other B vitamins to their active forms, but could this be circumvented by taking the active forms directly?
Yes, and this is what the methylation protocol does to some extent, e.g. by taking active forms of folate, B12 & B6.
But if B2 deficiency were the underlying cause then it would presumably be better to take B2 itself, since B2 is involved in things other than just converting the B vitamins (e.g. cellular energy).
How about taking the active B sublingually, so conversion is bypassed, and the vitamins are absorbed via diffusion?
Active forms of folate and B6 seem to be absorbed just fine from the gut (at least in my experience). B12 obviously is different, which is why sublingual so popular.