Stuck in a sticky situation with a friend...

I think you could frame things when you are with him to introduce him to what you are doing to change your life. Things like, "Hey, I found this recipe and it looks delicious. Let's make it together!" Ask if you can go for walks after dinner to "do something together that will get us out of the house." You can do similar things with his daughter. Hopefully, he'll see the changes in you and be inspired.

I would avoid even calling things "healthy." He probably won't want to eat "healthy," but would eat the same dish if it were "yummy."

I would share your enthusiasm with him... be excited about what you're doing for yourself and maybe he'll start to see that even little changes can help. It a tough situation, but unfortunately it might do more harm to bring the subject up to him. He could easily get defensive. My dad used to comment about my weight all the time and I started to resent him (not to say you're going to constantly be commenting on his like my father did to me). I didn't ask for his opinion so it hurt my feelings that he'd say things. Be happy about YOUR changes and progress, invite him to go for walks with you or offer to cook him dinner... Hopefully he'll catch the bug :-)

Wow, some of the replies are really just dismissive and cruel...

Obviously this person is your friend and you care about your friend very much.

Be positive about it -- he has an opportunity to regain his life and his health. And maybe you'd like to ask him to join you on your diet/exercise journey. It would be motivating for both of you.

Don't give up on a friend.

I was thinking the same thing :-/

Same.. people can be so heartless sometimes.

I think the most you can really do is set a good example. People don't change unless they want to change and are mentally prepared to make it happen, but sometimes seeing other people make positive life changes can have a ripple effect.

If I were in your situation, developing a relationship with someone I cared about, I would invite him to go for walks or out to do other physical things that allow you to enjoy each other's company. You might also consider inviting him over for a healthy meal that you've prepared or offer to make a healthy dinner for his family so you can all enjoy it together. You don't even need to tell them it's "healthy", but expanding his culinary horizons may spark a change.

Listen to this nice person.

I'm glad that you recognize that he has a very serious problem. It's a big help for the rest of us that we don't have to convince you of that fact.
Just like the alcoholic, he's addicted, and he's obviously creating an addict out of his daughter. Recovering addicts have no problem admitting that there was often one person who dared to say the hard things that made them stop, look honestly at themselves, and change the direction of their lives. It isn't necessary for someone to hit "rock bottom" to start to deal with addictions--they just have to get really really sick and tired of living their lives as addicts.
First off, you need to protect yourself from the behavior that goes along with his addictions. If you don't want to sit around and watch TV and eat and play video games and watch him eat--just like the spouse of an alcoholic doesn't want to watch the alcoholic drink--you don't have to. You can simply and quietly say, "I'm going to go to the library, or take a walk, or call my girlfriend and go feed ducks. I'll see you tomorrow." If he says anything negative about your weight loss, or about your healthy eating, or about your appropriate exercise, you can simply say, "I'm enjoying taking good care of myself." You're entitled to set boundaries.
Now, for the part about him. You have nothing to lose in writing a letter to him telling him of your concerns. Letter-writing takes the emotion and drama out of the picture, and gives him something tangible to re-read. Frame it in terms of, "I care about you, and I'm worried about losing you to early sudden death." No name-calling. (I don't think you would, anyway--you seem pretty sensitive.) No, "I'll only be your friend if you lose weight." But you can frame it in terms of, "I feel upset when I watch you feed your child terribly unhealthy food", and I'm upset when I watch you eat massive amounts of unhealthy food yourself. I want to enjoy a long lifetime of friendship together." You can offer to help him sign up for MFP, or ask if he wants to go walking with you.
I think a lot of this depends on what boundaries of your own he might be expecting you to cross. Does he get mad if you don't participate in the unhealthy behavior? Does he make disparaging remarks about your healthy life changes?
This is hard. Your first responsibility is to take care of yourself and keep appropriate boundaries in your own life. If this relationship goes on without his making significant changes, then you can expect just more of the same--but a lot more, because untreated addictions get worse over time, not better. I certainly wouldn't allow this to progress to a romantic relationship until he gets this under control. Uncontrolled addicts love their drug more than they love the people who love them.
I'm a nurse who has worked with a lot of addicts. I hope this is helpful. God bless you --you have a good heart.

Don't nag. Don't plea. Just be inspiring. Every now and then, maybe once every 6 months. Mention your weightloss and struggles, and offer to help him, if he's interested.

That's all you can do. Every adult gets to make their own choices. I was doing clinicals in the hospital. One patient was about 32 years old, in for recovery from having her lower leg removed from diabetes, in isolation due to infection. So I'm tending to her wearing a mask and protective suit. And she looks at her tray of food with the diet coke with it. Looks up at me, pleading "Can I have a regular coke?"

How do you tell someone "you're here because of all the regular coke you drink, and yet you're asking me to break the doctor's orders to get you a coke." People know that what they're doing is harming them. Be inspiring. Live how you want others to live.

This ^^

Maybe mention how much better you feel as you lose. What a difference making healthy choices have made in your life. But keep the comments about you, unless he makes it about him.

" However, if you love someone, shouldn't you try to do the best you can for them?"

Define best for them.

There's the problem. My mother tried to talk to me about being healthier and losing weight - and all it did was strain our relationship. Her concerns were grounded in health and science and love and care. But it didn't matter to my perception. There is a lot of emotional baggage I carry around mashed up with my weight. It may or may not be the case for him, I don't know. I do know that it hurt like nothing else to have my weight brought up because it felt like I was unlovable. Is that at all what my mother or husband ever said to me? Of course not - they are the two people in the world who love me the most. Is that what I heard anyway? Yep.

Hey, I think it's important to you to tell him that his choices are unhealthy and that it makes you sad. Do that. But then, it has to stop. Nagging gets you nowhere. You can lead by example. You can be brutally honest that your limits include not visiting his family because of their unhealthy behaviors and lack of food for you to eat. You can be very upfront about everything you are doing and why you are choosing that. But you cannot make him do anything.

Watch for openings, encourage with healthy foods you make yourself, invite him to walk with you - those are all positive, healthy things. But you will have to accept that if he changes at all, it will be a very difficult change and one that only he can come to and make.

It sounds like the two of you are close enough that it's worth having a frank discussion with him. However, everybody is right who says you can't make him change, he has to want it or it won't happen.

Be firm with your own boundaries. If you want a partner in a healthy life-style, that partner is worth waiting for. I married a smoker who has no interest in changing his self-indulgent habits. Early in our relationship, I put that behind me and concentrated on what I did like. Now I wish I had stayed the course for someone who wanted the same things that I did. I love this man, make no mistake, but listening to him cough and choke from years of smoking every morning and evening is really wearing me down, and I think following his lead in eating habits helped to get me where I am now.

But yes - my eating habits are ultimately my own responsibility; I am not blaming him, just acknowledging that eating with him led to eating like him.