1) The source for the opinions that one cannot learn health facts from Nochrim is in fact also a Gemara in Shabbos 86b, just a few pages away from the Gemara you have cited, Aryeh.

2) Rav Papa asked there what is the law concerning Zera of a Yisrael in the womb of a Kusis? We say that the Zera in the womb of a Yisraelis woman decomposes after 3 days. Does this also apply to the Zera in the womb of a Kusis? It could be that because Yisrael are always anxious to do Mitvos properly, this excitement warms them up, and this would not apply to a Kusis. On the other hand, because they eat non-kosher food it could be that this warms up their body, so the Zera may also decompose?

3) One learns from here that the Gemara understands that one cannot necessarily assume that the body of a Yisrael and the body of a Kusi can be compared. This Gemara is cited as the Halachah by the Pischei Teshuvah (Yoreh Deah 187:38) in the name of the Chasam Sofer (Yoreh Deah #175), who states that one cannot adduce a proof from their bodies to ours.

4) However, I do not think there is a contradiction between the Gemara in Shabbos 82a and Shabbos 86b. First, what Rav Yirmeyah mi'Difti saw when the Arab stood up and sat down repetitively was merely a support for what Rav Chisda had already said in the Gemara above. Rav Yirmeyah was not learning something new from the Arab, but it was only a confirmation of what Rav Chisda already knew. Second, the advice to give to someone unable to relieve himself would not seem to depend on the content of the diet (whether kosher or otherwise) of the person in question, but it would appear to be a physiological fact applicable to everyone regardless of what they usually eat or drink.

5) I would just mention that Rav Moshe Sternbuch shlit'a once remarked to us that to his regret too many Jews have also died from smoking (and so he writes in his Teshuvos), so it would seem that the facts prove that smoking kills just as many Jews as anyone else!

6) A further source is an interesting passage in the Me'iri (Ta'anis 21b, DH Makeh) I found a while ago which is relevant to our discussion and may reinforce what I wrote above.

The Gemara in Ta'anis (21b) discusses whether one fasts as a result of a plague afflicting the animals. The Me'iri writes that a plague afflicting one species of animal does not necessarily spread to other species of animals, so it is not necessary to proclaim a fast to ask for mercy on people, because a plague in animals does not represent a danger to people.

7) However, the Me'iri adds that if Yisrael live among idol-worshippers who are suffering from a plague, since there is no difference between their bodies and our bodies, a fast should be proclaimed.

8) We observe that the Me'iri writes that there is no difference between their bodies and our bodies. This seems to be contradicted by the Gemara in Shabbos (86b), and it seems to be a challenge to the view of the Chasam Sofer that we mentioned earlier.

9) I propose that there is no contradiction. What the Gemara in Shabbos (86b) means is that since we are excited about doing Mitzvos, this may make our bodies warmer and consequently the Zera in the womb of a Yisraelis woman may decompose quicker. However, this difference of body temperature certainly will not be a strong enough reason to say that if a plague is spreading among the Nochrim, it will affect only them and not us. Therefore, the Me'iri writes that a public fast day is to be proclaimed.

10) A similar idea may explain why the Gemara earlier in Shabbos (82a) is not a contradiction to Shabbos 86b and to the Chasam Sofer. It is true that there may be a difference between their bodies and ours, because of differences in temperament and consequent body temperature and also differences in diets. These differences might be significant sometimes. However, when Rav Chisda said that if one is unable to urinate, it is recommended to stand up and then sit down, and stand up and sit down again, and then Rav Yirmeyah mi'Difti saw an Arab with this difficulty do exactly what Rav Chisda suggested and it was dramatically successful, there is no reason to think that the different body temperature or diet of the Arab is why it worked. While there may be physical differences between different nations, there certainly are also many similarities.

Dovid Bloom