On another forum, someone was asking for tips on losing a significant amount of weight. I guess I was in the mood to do some typing, because I gave a pretty complete answer, which I thought I'd copy over to here in case I'm ever asked for my opinions on the subject again.
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I've weighed as much as 345 and am currently at 205, so I know what it's like to try to lose a significant amount of weight. I was also a fairly active fat guy, but the funny thing is that as you start losing a significant amount of weight, you'll look back on your current weight and say "what was I thinking?".
I still feel like a fat guy and it takes a while to change that mind set.
My recommendation for significantly overweight people is to keep exercise light and focus on diet. Walking is actually perfect. As far as diet goes, I would start out with a very limited menu, eating mostly the same thing every day (or having one or two options that you alternate between). The problem with starting a new diet is what they call "decision fatigue". Your willpower is drained by having to constantly make decisions about what you are eating and how you are exercising. My keeping to a set program and limiting your food options, you reduce the number of decisions.
Then, later into the program when it isn't a struggle to keep to the basics, you can start to get a bit more creative, but always fall back to your basic starting program if you find yourself falling off the wagon.
Get enough sleep. Actually, get more than you think you need. Change your priorities so that your diet, light exercise and sleep are your main focus. That might mean cutting out some TV time or not going out with friends for a while, so that you can get into this routine. If you are tired, your willpower will break quickly.
There are many ways to start a weight loss program, but I've always been a fan of just jumping in with both feet. Figure out your diet and just starting immediately. Drop all the fast food. Acknowledge that the first week is going to suck and just decide to at least go hardcore for a week. You are going to be hungry at times. You are going to want to quit. At the end of that week, you should feel good enough to keep going.
Look into what a good daily calorie total for you is. I would recommend something fairly aggressive, like 1800 per day. Then plan out each meal and get an exact count for everything you eat. Don't cheat, not even a little.
You have to look at this as life and death. If you knew a heroin addict and they were trying to get clean, you wouldn't tell them it's ok to shoot up sometimes as long as you get back with the program tomorrow. With obesity, it's the same thing. It's not the calories that matter when you cheat on your diet, it's the psychological spiral and physical roller coaster (the bad food makes you feel worse, which then makes it harder to find the willpower to get back on the program).
But, when it really comes down to it, it's a mental thing. You have to find something inside you that you can latch onto and keep going. For years I would get on a program like the one I described above, lose 30 or 40 lbs, then slowly put it back on. It wasn't until my son was born 2 years ago that I was able to really look at myself and my life, and make a long term commitment. Once I did that, it actually wasn't hard to lose 100+ lbs. Something just changed in me and it was just a matter of putting in the time to get the work done.
But obviously that's a difficult thing that is going to be different for everybody. I wish you the best of luck. It's a different world once you get to your goal weight.