I think the tantrums will happen. my dc hates to lose also.
What we do afterwards, when its all over, maybe a bit of time after dinner to gently discuss our feelings of how it felt. Then together brainstorm some ideas of what to try next time.
I was like that as a child but didn't really get any "help" to figure out my emotions and what I could do to learn to expect and control them.
The more practice the child has in "losing" then it won't be as quite a shock. Sometimes, I think, because the child intensely worked hard, tried very very hard, and the disappointment is just too much. Also, their intellect demands a lot from their little selves. So, for us, forgiving oneself, try again next time, despite losing it was a good "game" ... etc etc.
We have found that, with time and experience, it has helped. We work on "Just do your best" but that doesn't mean you'll win, get recognized, etc etc ... but to have a self-satisfaction of working hard and that is all one can do.
Hope that helps.
