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.
If money is not involved in this, then we may assume to be instinct bet or daring kind of bet that does not have to do with us playing games from the gambling platform, this is just a personal kind of desperation or dare we take on each other in other to know how strong or weak we are in doing something, but some could actually include money to their own, but i doubt it if they can fulfil the payment terms except a third party is involved and with the money to give the winner, because this is more of a personal or friendship bet and some may not take it serious like that.