I'm late to this thread, but I thought I'd share my own story. I got into hiking by way of photography, but as recently as 4 years ago I weighed in at 260lbs, on my tiny 5'5" frame(!!!).
I'd always wanted to go to Chimney Pond to photograph it, so a friend of mine and I made a reservation for October 14th, '06. This reservation was made 4 years ago tomorrow, to be precise (8/26). That's the day I started walking. I figured if I wanted to make it up there with gear, I HAD to start training, as prior to that, it seemed like I had a firm 1,000' vertical ceiling on any hikes I went on. I simply could not climb any more than that before pain/fatigue became overwhelming.
In early September of that year, to help train, I went and climbed Pleasant Mountain. It took me forever, with a ton of sweat, cramps, burning muscles, very frequent and long sit-down breaks, you name it - but I pushed on and made it. That felt good. A week later I went to Acadia with a friend and climbed Sargent Mountain. That was also hard, and gave me cramps, lots of sweat, etc, but I was starting to like the "view from the top."
I added a few more that fall (St. Sauveur in Acadia, Sentinel and South Turner in Baxter), and hiking was fast becoming my preferred means of exercise. In the end, we never did camp at Chimney Pond, as the forecast was for rain the day we would have had to hike up there, though we stayed at Roaring Brook instead and day-hiked to Chimney Pond the next day instead, a destination I made it to slowly but without incident. Between August 26th and October 14th I managed to lose 14lbs.
I had been heavyset since college, and for years, climbing up to Baxter Peak seemed an impossible goal, one that I didn't even bother striving to before, as what I had to overcome just seemed just overwhelming before I started losing weight. But after making it to Chimney, I had my eyes set on it for the next summer.
I continued hiking that fall, and started snowshoe-hiking that winter, first up Borestone, then Baldpate. The weight kept coming off. And then on a lucky day, 7/7/07, at this point weighing in at 187lbs, I climbed Katahdin for the first time
By July of 08 I'd lost 102lbs, and was hiking all the time. I haven't stopped yet:
http://betelgeuse.umeqs.maine.edu/chris/hikes.htm
Alas, my weight loss now stands at somewhere around 75bs, to my shame, but I blame that on moving to a new apartment that has a ginormous kitchen, allowing my to indulge in another hobby of mine, serious cooking. But I'm taking steps to make that hobby more healthy, and I'm again losing weight, very slowly this time, but that's probably a good thing. I'm down 17lbs since February.
Chris
PS if anyone is interested, here is a before/after picture of me at my two extremes. The one on the right is a bit weird, but I'll give kudos to anyone who can identify the object I'm swinging