IS IT BAL TASCHIS ON WHAT WAS EATEN (TO DO APICTVEESEN )OR ON WHAT YOU WILL EAT SINCE THIS WASN'T NECESSARY TO EAT ORIGINALLY??
IF ITS ON WHAT YOU ATE ARE YOU ONLY MKAIM A MITZVAH WHEN YOU FINISH DISSOLVING THE FOOD(AS YOU MIGHT STILL REGURGITATE & NEGATE THE EATING)?
I KNOW THERE IS SOME DISCUSSION BY MATZOH & EATING A KZAIS IF YOU THROW UP.
Rashi comments on Hefsed Ochlin - 'she'be'Me'av', which clearly answers your first question.
As for your second question, as long as you have not regurtitated, you have fulfilled the Mitzvah (although the Gemara is not referring specifically to any Mitzvah).
It would not seem logical to negate what someone has done, because he may undo it. (See also the Gemara in Chulin 103b, which discusses whether one transgresses an Isur of eating forbidden food when the food enters one's throat, or when it enters one's stomach.) Even if your final point is true, it is a question of negating the Mitzvah retroactively, but not of stopping it from having been performed in the first place.
Wishing you and yours a Kesivah va'Chasimah Tovah.
IF YOU ARE SAYING ITS ON WHAT YOU ATE WHY DOES RASHI GIVE A REASON THAT YOU ARE GOING TO EAT MORE SINCE YOU ARE NOW HUNGRY?WHAT IF THERE IS NO MORE? HE DIES RIGHT AFTER? HE DECIDED TO FAST?ETC
I'M SURE THE REASON IS ITS HEFSED MUMON.MEANING EVEN THOUGH HE HAS SOMETHING FROM THE NEW FOOD IT WOULD NOT HAVE BEEN NEEDED THEREFORE THE NEW FOOD IS THE PROBLEM.BY THE WAY I DON'T THINK THIS IS BAL TASCHIS ITS A NEW DIN OF HEFSED MUMON.BECAUSE HE IS GAINING FROM EATING IT BUT IT WOULDN'T HAVE BEEN NEEDED.
Rashi DH 'Mipnei Hefsed Ochlin' continues 'she'be'Me'av', as I pointed out last time. In other words the waste of food referred in the Gemara pertains to the food that he has already eaten. There is no other way of understanding Rashi.
When Rashi continues 'u'Mipnei Kach ... ', he is not trying to describe Hefsed Ochlin per se (after all, the man is hungry and needs to eat, exactly as you wrote). He is merely defining the waste of food. The food that he ate originally satisfied the eater, and it is only because he vomited it, that his satisfaction dissipated, causing him to have to eat again. In that case, the first food that he ate has been wasted.
It goes without saying therefore, that when the Gemara says 'Hefsed Ochlin', it means 'Hefsed Ochlin', and not 'Hefsed Mamon', as you suggested.
Wishing you and Yours a G'mar Chasimah Tovah.
be'Virchas Kol Tuv