"Since my frame is so large, I don't gain weight in my stomach, I gain it head to toe," he explains.
Over the next two years he reached 300 pounds, then 340.
He and Amy became foster parents, and a new influx of kids reminded Shack why he had lost weight in the first place. In April 2012, he decided he wanted to do a "century" bike ride of 100 miles. Between April and November 2012, he lost 100 pounds in training.
After the bike race he regained some, then dropped some. He recently started gaining again when he lost his job. But he's aware of his pattern -- and has a plan to tackle the extra pounds.
"I haven't been able to find my magic bullet," he said. "There's usually some motivation point that makes me want to lose weight. Once I hit that goal, I kind of lose my motivation."
Amy has maintained her goal weight of 160 pounds for more than three years. She finished a half marathon in January. She stays active -- "when you have six kids, they are your activity" -- and continues to monitor what she eats closely. She knows people have gained back their weight even after gastric bypass surgery.
"I'm going to battle my weight for the rest of my life," she says.
No one's weight loss story really has an end.
The goal of a healthy lifestyle is to avoid ending the tale too soon.