Allergens in the diet may well induce inflammation in your intestines, that inflammation will prevent absorption of the important nutrients. Prolong chronic inflammation takes a while to heal. The only outward symptom might be a little acne or reoccurring dandruff.
Just an aside, an all vegan diet has none of the B12 Vitamins you would need. It is a multistage process to get the B12 from animal proteins to your neural system. I would keep to the diet but check out the book. The apple cider vinger bit might sound like hersay but Danno is likely spot on in his recommendation. Whats a couple table spoon of viniger going to hurt? At worst it might cure some heartburn, which is usually a common tell to an out of wak ph balance
I remember a while ago Dr. Mercola recommended diluting raw, organic apple cider vinegar with a bit of water since it can cause severe burning going down, the water diluting it solves this problem. It is also a somewhat helpful weight loss aid, but that is another discussion for another day.