QUESTION: The Gemara relates that the Kohanim who served in the Beis ha'Mikdash had chronic gastrointestinal problems as a result of the large quantity of meat of Korbanos that they ate. Since they were involved in the Avodah, they were unable to drink wine to assist their digestion, because a Kohen who performs the Avodah may not drink wine (Vayikra 10:9).
The RU'ACH CHAIM (Pirkei Avos 3:3) proves from the Gemara in Yoma (73b) that when the Kohanim ate the meat of Korbanos in the Beis ha'Mikdash, they had no waste products. All of the meat was absorbed into their bodies, just as the Man (manna) was absorbed into the bodies ("Nivla b'Eivareihem") of the Jews in the desert (Yoma 73b), since it was a food comprised of spiritual components.
RAV SHMUEL ROTHCHILD in SEFER PEIROS TE'ENAH quotes the SHALMEI TODAH (end of 1:5) who says that the Gemara here seems to contradict the assertion of the Ru'ach Chaim. If the meat of the Korbanos was absorbed into the bodies of the Kohanim and produced no waste products, why did the meat cause digestive disorders?
In addition, the Peiros Te'enah cites the KUNTRUS DIVREI TORAH (9:5) who asks that the verse says, "Shomer Mitzvah Lo Yeda Davar Ra" -- "He who performs a Mitzvah will know no harm [from it]" (Koheles 8:5). The eating of the meat of Kodshim is a Mitzvah, as the Gemara says in Pesachim (85a; Rashi there, DH v'Ha Tanya). Why, then, did the Kohanim suffer from it?
ANSWER: The KUNTRUS DIVREI TORAH answers that perhaps the meat of the Korbanos caused stomach problems only when the Kohanim did not eat the meat with pure intentions, l'Shem Shamayim. The Gemara in Pesachim (3b) relates that it happened that some Kohanim did not have pure intentions when they consumed Kodshim (for example, some Kohanim ate the Lechem ha'Panim with haughtiness). The Gemara in Pesachim (8b) implies that the principle that "he who performs a Mitzvah will know no harm" applies only when one does the Mitzvah with pure intentions, Lishmah. One who performs the Mitzvah for his own personal benefit has no guarantee of protection.
Similarly, perhaps when the Kohanim ate the meat of the Korbanos for their own personal benefit, the meat was not absorbed completely into their bodies and would cause digestive problems. (The Ru'ach Chaim himself suggests such a difference with regard to an ordinary person. When one eats his meal entirely l'Shem Shamayim, the waste products of the food are "burned by his Torah" and leave only the pure and necessary part of the food, which becomes completely absorbed into the body.)