Have you spoken to him about your concerns? Letting him know your fears about losing him could potentially help to motivate him.
Maybe all the offers are too overwhelming for him? Maybe they reinforce a sense of shame or powerlessness or inadequacy?
I have seen some documentaries on companies taking the initiative and running health programs during working hours.
Have you spoken to him personally? What would motivate/ help him? A financial incentive? ?? What would he consider rewarding?
Could you start with offering to pay for a medical evaluation? Mandating one. Would he be resentful of that?
Sometimes when people pick on a flaw it can reinforce that. It can feel amotivating to have your weaknesses highlighted especially if you are sensitive to them.
The doctor here has some weight loss suggestions in his earliest blog. I expect he advises people about weight loss a lot so he should have some good ideas and advice.
I also like the advice of a former expert at medhelp on emotional eating. He has a website (shrinkyourself.com). If you subscribe to their newsletter you receive free tips and advice on how to overcome emotional eating and lose weight.
Does your employee have a tidy work space? If not the problem could be emotional and counselling could be beneficial. It is said that our outside world is a reflection of what is going on in our heads.
I hope the doctor here is able to do your question and concern justice.
I think it's wonderful that you and your other associates are looking out for your colleague. But you are in a tough position. If you have made it clear that you are concerned about his weight issues and he has not responded to your offers to help, there may not be anything further you can do in the workplace environment. A more personal approach taken outside of work could be an option. And you can ask directly, "We are here to help you - do you feel that you need our help right now?" If the answer, is "Thanks, but no," then unfortunately I think that there may not be much else for you to do right now, as frustrating as that may be. Take care.