Yeah, sort of bringing an old thread back from the dead, but I have a similar story...
Through sheer recklessness, I gained a ton of weight a few years back. What really caught my attention was when I tried putting on a pair of size "XL" Depend underwear - and they ripped in half as soon as I sat down. I pulled out the old bathroom scale and climbed on to see what it said. When it just flashes "-E-", that's a bad sign. Given the weight range for that scale, I was well over 400 lbs. I had known that I was seriously overweight for quite some time, but that seemed to be the moment of epiphany.
I immediately started trying to cut back on how much I ate - no more going to the pizzeria twice a week, no more going out for hot dogs every afternoon, no more "snacking" on what most would consider a full meal - certainly no more doing all of the above in a single day. I restarted my membership at the health club I had quit going to 3 years back and made an effort to go at least once a week.
Things started slowly at first - after an initial burst of activity, I started making it to the health club perhaps once every other week, or every third week. I cut the take-out pizzas down to one large with breadsticks a week, and reduced the snacks throughout the day to the absolute minimum I could bear. Even that had an impact - after a month the Depends stopped tearing apart on me, and eventually I could even get a brief to stay taped on again. The scale started showing meaningful readouts again as well - I was actually glad when it showed "398.0".
Things kept going slowly until October of last year - I had been working as a newspaper carrier for about 2 years while saving for school (no, I don't wear diapers while I'm working), and started doing a short walking route in addition to the motor route I had been doing. That short route doubled in length when the the kid who was supposed to take over an adjacent route bailed - while I was waiting to pick up my papers, the manager came out and asked me if I wanted another route! Needless to say, this meant a lot more physical activity for me every day.
At first, I was panting and sweating profusely throughout the whole daily ordeal, but after only a few weeks I found I was having a much easier time with it. The scale was showing ever smaller numbers - now around 340 - and the diapers I was wearing to bed each night seemed to be getting a bit more comfortable. The pull-ups always seemed to dig into my legs before, but now they did not. The tapes on the briefs were getting noticeably closer to the front as well. Encouraged by this, I started going to the health club more often and cut back on the food even more - the weekly pizza was now a medium, and sometimes I'd just skip the hefty lunch altogether. By February, I was below 300 lbs!
It was around that time that I decided to try something silly - I went to the store and bought a bag of Underjams. That store had just started carrying them and they were a bit hard to find, on the bottom shelf buried amongst the Easy-Ups. I got them home and tried them out - with some careful stretching, they fit! Sure, they snapped apart after a few minutes but that got me excited! The next time I was at the store I grabbed a bag of GoodNites underpants to see how they'd fit - unfortunately, that didn't go as well; I couldn't get them past my still-too-thick thighs. Close, though!
A few months later the new GoodNites underwear came out - word was that they were softer and stretchier, more like Underjams, so I decided to see what would happen if I tried one on. I was down to 280 lbs by that point, so I thought I might have better luck in any case. I picked up two bags of each of the Girls' and Boys' style, plus the last of the GoodNites boxers they had in stock - they were marked "clearance" so I figured it might be my last chance. When I got home, I actually tried one of the "boxers" first, since the bag was torn open. It was painfully tight, but I eventually squeezed myself into it. After about an hour, I decided to "use" it, then took it off and jumped in the shower before bed. While preparing for bed, I tried on one of the new "underwear". It wasn't nearly as tight as the boxers, but still put quite a squeeze on my hips, and left some unpleasant-looking red marks on my thighs in the morning! I'd come a long way, but still had a way to go...
That brings me to now. I'm down to 250 lbs, have quit going to the pizza place entirely (well, once a month) and now make every effort to go to the health club at least 4 times a week. Those GoodNites fit much better now, they're still too tight for practical daytime use but they don't dig big red gouges in my legs anymore. My goal at present is to lose enough weight to be able to wear the old-style GoodNites underpants I have stashed away, and eventually to get into the far-less-tolerant 2008 GoodNites boxers I bought 2 cases of a few weeks back - unlike the soft, flexible ones made today, these are made of a tougher paper-like material that rips apart as soon as I get them over my thighs!
So, as it works out, diapers proved to be the best weight loss motivator I could ever ask for.