I checked and I don't think this has been asked before. I'll preface this question with the fact that my husband and I just started trying to conceive. (Yay!)
Anyways, as we all know, SAD dieters' hormonal balances are often way out of whack. Is it possible that, as someone who's been practicing Paleo relatively faithfully, I would not initially generate the amount of HcG necessary to trigger an early pregnancy test (meant for the "normal" population)? It's just something I've been wondering.
Recently I was reading a thread (on another forum) and I was pretty surprised by the number of women who said they didn't test positive until they were pretty far along. I also saw a number of people in the thread who had complications of one sort or another (preeclampsia, gestational diabetes, etc). So while I don't know if the two issues were related, I did find it interesting. The forum isn't a diet/health/whatever forum, so these women were a random sample of the population.
If diet does anything in this case, I would hazard a guess that at the very least it would help regulate hormones enough that you would test positive, but not necessarily an early positive, just an on time one.