Just because your friend is dieting, it doesn't mean you have to change your life. But some thoughtfulness will go a long way with someone who is doing something really difficult in an attempt to change his or her life for the better.
  1. Suggest ways to hang out that don't involve food
    Watching a movie, going for a walk, going rollerskating, etc. When you're dieting it seems like everything in life revolves around food; it's nice when one thing doesn't.
  2. If your hang outs traditionally do involve food, maybe let your friend pick the restaurant or at least suggest a couple.
    Your relationship isn't all about him/her, but dieting is difficult, and this could really help him/her out. I'm usually just looking for restaurants that publish their nutrition info so I know what I'm getting into.
  3. In the same vein, decide on the restaurant in advance.
    When I am dieting I will almost never make a good choice in the restaurant, surrounded by smells and menus with giant pictures of food. If I know where I'm going in advance, I'll have a plan when I arrive.
  4. Don't assume he/she will be up for drinks.
    While your friend has not turned into a monk, drinks are "empty" calories, and therefore one of the first things to be cut when a person is watching what he/she eats.
  5. Ask how things are going occasionally.
    Each person is different. Some people may not like talking about their diet plan and some people want to talk about it all the time. Personally, I'm not typically going to bring it up, but it's nice when someone checks in.
  6. Don't tell your friend not to eat or drink something.
    If your friend has decided to have a beer or eat dessert that is his/her decision. Your friend may be making it from a logical place, weighing the decision against the other things he/she's eaten that day or how much exercise he/she's accomplished. Or he/she may be making from a place of emotional distress. Either way, it his/her decision and that person needs to be able to make healthy choices on his/her own. You attempting to enforce healthy eating only makes your friend feel mad/bad.
  7. Don't pass judgement on their diet plans or offer advice on how they should eat.
    If you're not someone who struggles with their weight, your friend's diet may sound weird. They don't need to know you think that. And unless you're asked, please don't offer advice.
  8. Don't offer them food, even if it's healthy.
    I'm very methodical when I'm dieting. I follow a plan, and I know what to eat when. You're extra food just throws me off.
  9. Watch out for mood swings.
    Dieting is emotional. Sorry.