In the Garden of Eden, Adam, Eve and animals were instructed to eat food that came from plants (Gen 1:29-30); after the flood, God allowed Noah to eat all animals, but told him not to consume their blood:
“… everything that creeps on the ground, and all the fish of the sea, into your hand they are given. Every moving thing that is alive shall be food for you; I give all to you, as I gave the green plant. Only you shall not eat flesh with its life, that is, its blood. (Gen 9:2-4 NASB)
It may be surprising, but God told Noah to eat כָּל־רֶמֶשׂ אֲשֶׁר הוּא־חַי (kol remes asher hu chay) “all living things that creep/crawl.” This is a broad-sweeping description that implies the totality of animal life. Indeed, רָמַשׂ (ramas) means “to crawl” or “creep”; in other words, “to move close to the ground” – thus, רֶמֶשׂ (remes) can be translated as “reptile” or even “insect.” For Noah, not only insects and reptiles, but all species—including those that the Torah would later deem unclean—were now on the menu.
Noah is the only man called אִישׁ צַדִּיק תָּמִים (yish tzadik tamim) “righteous” and “perfect/ blameless” (Gen 6:9). Even long after the flood, biblical authors continue to call him “righteous” (Ezek 14:20; Heb 11:7; 2 Pet 2:5). Despite his Gentile status and unlimited menu, Jewish sages saw Noah in a very positive light, as the model for a righteous non-Jew (cf. Talmud, b. Sanhedrin 108a; Genesis Rabbah 30:10).
Noah clearly knew the difference between clean and unclean animals even before the flood. He was told to bring “clean animals” הַבְּהֵמָה הַטְּהוֹרָה (habehemah hatehorah) in sevens and “the animals that are not clean” הַבְּהֵמָה אֲשֶׁר לֹא טְהֹרָה (habehemah asher lo tehorah) by pairs into the Ark (Gen 7:2-3). Curiously, animals were categorized this way even before they were considered a food source.
Noah could have eaten unclean animals, and he still would have been considered righteous in God’s eyes. It may be hard to reconcile this if one understands the dietary laws of Leviticus 11 and Deuteronomy 14 as laws for all humanity (Jew and Gentile alike). But the Torah defines righteousness for Israel by specifying that certain animals are “unclean/clean to you” – that is, only unclean for the children of Israel (cf. Lev 11:4, 5, 6, 7, 8, 29, 35, 55; Deut 14:7, 8, 19). However, as non-Israelites, Noah and his family could have eaten any food they liked without becoming unclean or unrighteous.