I do not like this kind of bet. A bet that no money nor anything is involved. I mean nothing is involved because one of you can decide not to fulfill the betting promise. Example is if your friend did not lose more weight and still decide not to pay for the meal? This can happen. I do not bet with people. I prefer to go to casino or bookie to bet instead.
Well maybe you aren't seen the full picture, In my point of view it is a win-win scenario if you partner/friend doesn't fulfill the agreement at least you still reach your goal ( lose weight, do some daily exercise, read some books, IDK you name it!),
Because the only way to really lose in this scenario is when you fail to your self in achieving your own goals.Another thing is that you always can have some extra friend as escrow to ensure the fulfill of the bets/aggrement