I can definitely imagine the stereotype being caused by a combination of climate differences and lactose intolerance with ethnic prejudice. That is:
—“I hear they take a lot of milk, butter, and cheese, every day!”
—“Every day?! But those things spoil so fast, they must be eating rotten milk all the time—and it’s so bad for the digestion, they must always have flatulence and diarrhea. Ugh, those barbarians are so gross.”
—“I hear they take a lot of milk, butter, and cheese, every day!”
—“Every day?! But those things spoil so fast, they must be eating rotten milk all the time—and it’s so bad for the digestion, they must always have flatulence and diarrhea. Ugh, those barbarians are so gross.”