From your question I can't work out if you're more concerned about your wifes' weight concerns, or irritated with her habit of borrowing your own portion of snacks, side dishes, etc ("depriving me of mine").
If it's her weight, you getting irritated by her act of borrowing from your share isn't going to help her address her concerns about putting on weight. If this is the main issue, it sounds like it might be useful to sit down and have a calm and supportive conversation about how you would like to help her work towards her goals of losing weight. This might involve you sacrificing your own snacking/ordering side dishes, etc at least for a while. In a way, make it a team effort - you are forgoing things to remove temptation. Naturally this will only work if you genuinely want to help; if you're going to be resentful there's no point, as it'll just create unnecessary tension and also make her feel even worse. If you need an example, when I was breastfeeding our children I had to restrict several foods due to them having food intolerances. In each case, my husband matched my restrictions so that we were both in the same boat - ie didn't eat dairy, nuts, etc - because it was a team effort. It's an act of kindness and solidarity that really helped me (as a foodie!) and also had the added benefit of being a very loving gesture, so our relationship got stronger as well.
Now, if the issue is more about you simply being irritated at her being a hypocrite - ie, eating your portions when she's trying to lose weight - maybe rather than getting annoyed, you could turn the situation into an opportunity to (again) strengthen your relationship with a romantic gesture. Ordering a side at a restaurant? As the waiter for two small plates, or to bring divided on two plates, that way you're sharing the dish. Same thing if a bag of crisps at home - take the bag you were going to have for yourself, and divide it using two small bowls. Offer her one of them - you still get your snack but without dwelling on being "deprived", and your wife feels loved.
Now if none of the above feels right to you, or you bristle at the thought of sharing in these ways, I'm going to guess there's something else going on. You may well wish to seek the support of a couples therapist.