During training you cannot DIET. It's a mental thing you must change. I'm only 75% of the way there, but I've made progress.
You have to start making permanent lifestyle changes. And you know what, it's really hard. Not impossible, but hard.
So, I'll start since I'm chiming in like a know-it-all!

For me, one of the first lifestyle changes were
1. No fried foods. None. Nada. Nyet.
2. No McDonalds (CAVEAT: Still got Diet Coke, Fruit and Walnut snack, and Scrambled Eggs in a bind).
3. Drink more water. OMG More water. No less than 3L/day.
Some people have to go cold turkey. Usually, that's not me. I wean myself off stuff.
Some people (women mostly, but men too) are emotional issues. This may mean addressing those deep dark secrets.
You will find your palate changes over time. I no longer WANT a BigMac but yet I used to eat lunch at McDs every day for years. Now, I couldn't stomache one. Ug, I'm queasy right now.
p.s. Fat people are pathological liars. Accept that you can and will lie to yourself and others and you will make progress in beating the lies. I STILL find myself doing it, you BELEIVE you are telling the truth (hence pathological part) but you're not. It's something about the way the brain is wired.
Before anyway flames me... I'm not slamming ANYONE. I am preaching the truth, at least as I see it and/or it applied to me.
I am currently 236lb 35yo male, down from 322lbs 3 yrs ago. No activity to Ironman 70.3 last year (and 2 half marathons, half dozen sprint tris, various 5k/8ks, etc).
------------------
Yup That's me[/URL" target="_blank">