Yo-yo dieting slows metabolism so that’s part of the problem. It’s about lifestyle change rather than a quick fix. It’s about incorporating more activity and filling up on plants and water. But that’s not the question and it’s not what anyone wants to hear. He should just tell her that she’s too fat. It’s not what he signed up for when he married her. Laziness is a turnoff. Attraction is important. Her health even more so since they’ve got kids. At the same time, I understand how having kids contributes to weight gain because your life has to revolve around them, so he should also find a way to make sure she has more time to herself so she can get her workouts in.