The most important part IMHO is motivation, diet and identifying your bad habits, so you can avoid them. I peaked at about 22 stone when I was 28, mostly due to portion size (despite typically low fat meals), snacking/beer, a strong aversion to exercise and Id given up trying to control my weight after many failures. I then found motivation heading for 30.. cut down the calories, severely restricted the drinking, took up running, weights and later cycling and lost about 6 stone slowly over 2 years and momentum kinda gathered with me doing more and more exercise each week watching my weight and race times dropping, which also allowed me to eat and drink more. I stopped running with friends when they gave it up and winter set in and I took a couple of month break, after which I was slower, significantly heavier and realised Id never realistically train as intensely on my own or beat my PBs, so struggled with motivation and focussed on cycling more instead but ive kept slowly gaining weight.
To start with the motivation came from going on holiday with friends and being exhausted just walking around all day and looking for places to sit down rather than joining in the fun, but the problem I have now is that despite being 18.5 stone (at 6'2) my fitness is still pretty decent, I can comfortably run a 10k tomorrow or a half marathon at a few weeks notice, or go out and cycle 50+ miles, so I dont feel as much need to lose weight as I did. It's finding a big enough reason to lose the weight, at the moment im thinking about running a marathon next year and with that in mind have lost a stone in the past two months but id want to lose another 3 at least, and ill need another reason after that.
I just can't comprehend being 22 -23 stone. I've always weighed about 10.5 - 11 stone. Some times a bit less or a tiny bit more. You have to do some serious eating to get that fat IMHO. It's not just the visible fat either but the excessive fat that is stored around your vital organs eg liver and heart. Yuck! Respect to those who have lost all the weight. Stay off the pies and pizza.
It only takes something like 500 calories extra per day to gain a pound a week or 3.5 stone a year so its quite easily done gradually over time without necessarily eating lots of junk food or a high fat diet if you just eat a bit too much.
It's hard to comprehend from both perspectives, a lot of people who have been heavy their whole life dont realise how much easier things are day to day without several stone extra bearing down on you.