וַיָּשִׂ֥ימוּ ל֛וֹ לְבַדּ֖וֹ וְלָהֶ֣ם לְבַדָּ֑ם וְלַמִּצְרִ֞ים הָאֹכְלִ֤ים אִתּוֹ֙ לְבַדָּ֔ם כִּי֩ לֹ֨א יוּכְל֜וּן הַמִּצְרִ֗ים לֶאֱכֹ֤ל אֶת־הָֽעִבְרִים֙ לֶ֔חֶם כִּי־תוֹעֵבָ֥ה הִ֖וא לְמִצְרָֽיִם׃
Il fut servi à part et eux à part et à part aussi les égyptiens ses convives; car les égyptiens ne peuvent manger en commun avec les hébreux, cela étant une abomination en Égypte.
Chizkuni
כי אם הלחם אשר הוא אוכל, “except for the food he used to eat.” We have learned already in Genesis 43,32, that the kind of food that Hebrews ate was considered as an abomination by the Egyptians; it is therefore understandable that Potiphar would not allow Joseph to prepare food in an Egyptian kitchen. In Isaiah 30,7 the prophet speaking in the name of the Lord, describes the Egyptians in derogatory terms. In their haughtiness, they looked down on all other nations, on Hebrews especially. [This is also clear from the way Mrs Potiphar refers to Joseph as a lowly subhuman category of being; (39,17). An alternate explanation: Potiphar entrusted everything to Joseph, the only thing he found fault with was his eating habits; we know the prejudice the Egyptians harboured against the Semites on account of that from Genesis 43,32. They could not bring themselves to eat at the same table as the Hebrews.
Da'at Zekenim
כי אם הלחם אשר הוא אוכל, (literally) “except for the food that he ate.” We find two more references in the Torah describing that the Egyptians and Hebrews had a mutual distaste for each other’s eating habits and menus. (Compare Genesis 43,32, and verse 9 in this chapter, where Potiphar’s wife is described as out of bounds to Joseph [similar to his bread. Joseph was not afraid to make this comparison. Ed.]
Ibn Ezra
Except for the bread he ate. He would not allow Yoseif to touch his bread because he was a Hebrew; see 43:32.