The Rebbe warned us very strongly not to eat raw onions.³⁵⁷ 29a; Tosafot ad loc. 29b, “Mipnei"; Ta'anit 30a, “Erev"; Yad Chazakah, Dei'ot4:9. It made no difference whether they were mixed with oil, fat or eggs, even for Shabbat.³⁵⁸, quoted in Ta'amey HaMinhagim #367, p. 169.

footnotes: ³⁵⁷ Cf. Eruvin ³⁵⁸ Many people had a custom of eating chopped eggs and onions on Shabbat. This custom is mentioned in Geulat Yisrael

The Rebbe ridiculed this practice, saying, “How can they claim that it is a good custom to eat something as harmful as this?”

The Rebbe said that onions are harmful in many ways and counted out numerous illnesses that can be caused by them. Although the details were not preserved, the main lesson was that onions should be avoided, even if they are mixed with something else on Shabbat. The only safe way to eat them is cooked.

The entire conversation came about when we mentioned to the Rebbe that we had heard that the Baal Shem Tov had spoken very strongly against eating raw onions. The Rebbe agreed that this was true and began to reckon numerous reasons for it. It was at this time that we heard the above.