I've been married for 15 years . . . and there is absolutely no way my husband would refuse to talk to me about something important to me. That would be a HUGE issue in my house. I think you should address that first.
Ultimately, it's your body and your decision. I know it's a lot harder without support, but if this is something you really want, you may just have to do it. Maybe he doesn't fully understand the health risks at your current BMI? If that's the case, make sure he does. It's not a question of "if" you're going to have health issues - it's really a "when."
I know it's not exactly the same thing, but my husband was not supportive when I first wanted to go back to school. He thought I was going to be wasting money and I wouldn't follow through (in fairness, I was young and a little flaky then). When I got my bachelor's degree, I got to say "told you so." When I got my master's, I got to say "SUCK IT, DH." So . . . I do understand that it's hard to make a decision without your husband's support, but I also know it can be done!