We've been together for almost four years now, and in that time we've both put on weight. I've put on 12kg, and I think he's put on about 15kg, but it doesn't seem to be as noticeable on him, but we are both now in the Unhealthy weight range.
I've been exercising lately, and have improved my diet as I want to get back to being healthy and have now lost 5kg, however he wont support me. He is always saying things like "why do you have to lose weight, I don't like skinny girls". He also does things like asks me if I want to get a coffee, and then when I say yes, he takes me to McDonald's!
I don't' know what to do, any help anyone else has would be really appreciated.
(Every other part of our relationship is great at the moment)

If he is a real man, he will be happy with your decision.

A person that does not support you in being healthier and taking care of yourself is not a person that truly loves you.

tell him that if he goes running with you, you'll give him a present or sumthing he likes in return.

Well, I'm guessing that he just wants you to know that you don't have to lose weight for his sake. And wants you to feel good about yourself.... for who you are.

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just tell him how you feel for example could ou please help me loose weight and stop tempting me to go to fast food restraints and help me loose weight but since he is your boyfriend try to tell him more nicely.

let him know that its your body and you can do what you want with it. you love him and he knows that. he just needs to understand that if you dont feel comfortable, of course you do what you need/want to. not to be mean to him or anything but if you dont feel comfortable you should do what you need to. and if he really loves you, he should at least try and support you even if its one 1%.
hope this helps=

Tell him that it's for your health, and he should be doing the same. Once you lose all your weight, he will be jealous and want to start eating healthy too. My boyfriend was exactly like him at one point, then I dropped about 20lbs that were VERY noticeable, and he jumped on the bandwagon as well. If he offers to take you somewhere for coffee, tell him that YOU want to pick where to go! And if he takes you to McDonalds just show him up- it sounds like he's trying to set you up for failure. Don't let him do that to you! You can do it girl!

Although it sounds like every other aspect of your relationship is stable, it sounds like your boyfriend isn't happy with who you want to be. Be it that he truly likes heaver set women, or he is afraid that your being fit will make you an easier target for other men if he continues to gain weight, it seems odd that if he truly loves you that he wouldn't like you for how you looked when you two first met and how you still want to be. Considering how it seems he may be trying to sabotage your weight loss success, that is not a very good sign of respect for you.