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.
There are different types of bets and what we focus on discussing on this board is gambling bets, this are bets that are done mainly through gambling establishments so that nobody tells you stories when you win. There are other types of bets like challenging with others that you can achieve something or get a task done, this types of bets or challenges doesn't necessarily require putting money at stake. I'll personally prefer to bet on gambling sites if i want to gamble with my money, I don't like to do money bets and challenges with friends because I've known from experience that money can come between friends, so it's better to avoid betting with friends.