I seriously doubt that your husband thinks he's not overweight. it's probably the dead opposite. I can almost guarantee that his weight and size are the 2thing that he is most aware of.
It's a very slippery tightrope to walk really. He knows he needs to lose weight, or at least improve his health. But knowing something and using that knowledge to take a pro-active approach are 2 completely different things.
I'd go as far as to say that his problem is that he's got food and eating issues (most likely disordered eating--I bet he virtually starves and then binges, doesn't he?), as well as self esteem and self confidence issues. It's not surprising that the lower your self esteem and confidence are, the less motivation you have to tackle whatever your problem might be, be it weight, smoking, drinking, gambling, compulsive lying.....kleptomania......compulsion and addiction are very complex situations.
I understand his reluctance to exercise. When you're very large, not only is it difficult to do physically, but it's difficult mentally and psychologically as well.
When I was at my biggest, I knew I needed to move more to facilitate the weight loss, but I just couldn't bring myself to do it. I was ashamed of the way I looked, that everything jiggled and wobbled, that I looked ungainly, and didn't/couldn't move all that gracefully. I was
embarassed to be seen actually trying to change all that.
It doesn't help that very often you're so self conscious about your appearance, and then some smart arse will inevitably make a comment, or shout an insult, or a make fun of you in some way. and that really hurts, especially when they're screaming fat hatred at you while you're trying to become less, or not, fat. I personally don't know a single soul who's ever felt inspired by being berated or ridiculed. If anything it makes you give up even more.
so, when you suggest he go walking with you, he
knows, deep down, that you're not making fun of him or putting him down, but he's probably had abuse heaped on him so much in the past (probably very recently too), that he can't bring himself to help himself. It's psychologically scarring. Those scars are the hardest to get rid of.
Try this: say to him only once "I'm going for a walk. You want to come with me?" if he declines, then say nothing else other than, "Ok. I'll be back after while." and then go out, enjoy your walk, and when you come back don't even bring it up. Even if the walk was glorious, and you feel wonderful and saw all kinds of really cool things, he will only take it as you needling him. So just don't say anything else about it after you go out and come back.
Keep doing this. don't say anything negative about him not going; don't make a face or do that heavy dramatic sigh that so many are so good at because it implies disgust (even if that's not how you mean it, that's how he'll take it). Like I said, keep doing it, and don't make a big deal about it. It's kind of like......
.......when you're trying to get your kid to try, say, broccoli. The more you push, cajole, beg, pleade, hammer, pester, or try to guilt them into it, the more they will dig their heels in and refuse to try it just on principal.
It's what I call being supportive silently by example. Offer the healthy option in a simple manner:
"Would you like some broccoli?" (if no) "Ok". and go about your business
"Want to come for a walk with me?" (if no) "Ok". and go about your business
It can take a while for it to take root, but if you keep persisting in a non-aggressive, non-judgemental, non-threatening way, he's more likely to adopt the healthier habits. People generally tend to be copy cats; mostly we want to be like everyone else.
Of course it is not fail proof. Little in life is! But it's worth a shot. You can always witch tactics. Good luck!