Husband needs a health overhaul

My husband recently had a severe virus which has left him with ongoing health issues. The doctor has put the hard word on him and told him to lose weight, get fit (i.e. move more and build strength), quit smoking and generally tidy up his health. Problem being that he's not following those instructions, with the exception of giving up smoking. His blood pressure is okay which is about all he has going for him.
I'm the proactive type so I would have liked to have thought that I'm setting a good example, diet and exercise -wise, but he's not following my lead.
I do the food shopping and cooking, and he takes lunch from home but I'm 99% sure he buys junk food while he's at work. Okay, 100% sure.
His health issues will be lifelong and have the potential to end his working life very soon if he doesn't make radical changes.It's going to impact on our whole family if he does nothing.
How can I best help him before it's too late?