Growing up, David Kirchhoff never had a problem with his weight.

That’s because his parents wouldn’t stand for snacking and allowed their kids only one “treat” a week.

When he didn’t have those rules to rein him in anymore, Kirchhoff watched as the numbers on the scale gradually ticked upward to 242 pounds. That started to change in 2000, when he got a job at Weight Watchers. He became not just the president and CEO of the company, but also a member.

Last week, Kirchhoff was promoting his book, “Weight Loss Boss” ($26; Rodale), which explains how he managed to lose 40 pounds.

Q. You were on basically the opposite of a crash diet. Why did it take you nine years to lose the weight?

A. Because it takes most people that long. People who struggle with their weight, it’s never a straight line. When I first started, I lost a bunch of weight quickly. I got cocky. And then the weight came back. I wasn’t dealing with the underlying issues and establishing new habits. So when I finally got there, I felt I’d done it the right way, and that’s what’s helped me keep the weight off.

Q. One of your new habits is exercising regularly. What’s your technique to make sure you do it?

A. I now work out six or seven days a week. It’s an old trick to set your gym clothes out the night before, but it’s incredibly effective. The alarm goes off at 5, and I stand up. That’s the only willpower I need to summon. Some people need a lot of variety. I’m not that person. What I like about my routine is that it’s on autopilot. But whatever works for you, as long as the process becomes habitual.

Q. You used to blow your diet and exercise plans when you traveled. How do you deal with that now?

A. I try to keep my routines consistent. I stay in a hotel with a good gym, and I have the same breakfast I would have at home.