Kirstie put the weight back on—plus an extra 10 pounds—over a year and a half, about the same amount of time it took her to lose the original 75 pounds, she says. "My whole life I battled with 15 to 20 pounds. I either weighed 125 or 145. ... To me, it was a big deal. That was sort of my life with weight loss," she says. "Then when I gained weight the last time—really gained weight and lost it—I honest to God thought: 'This is it. This will be the last time I ever do this again,'" she says.