Overweight husband

I been married for 6 years. My husband been working at the same job for 2 years. Like for a year and a half he been complaining about his feet hurting a lot. He had been to doctors and wasting money on shoes etc. Well didn't occur to me until recently that when he started working there, he gain sudden weight. Over 40 pounds. I don't see how he gained that much. How can i help him lose weight? How can I convince him that that could be the problem of why his feet hurting?