My mother aggressively called my brother fat

Tonight he tried on a new pair of jeans that didn't fit him, so my mother started screaming about how fat he was (she used a more heavy term that I don't think has a proper translation in English) and that he had to dress with ugly clothes because nothing fits him. She repeat herself for a while, yelled that he has to eat less and went away.
I agree that he needs to get thinner, I'm afraid it might start to get toll on his health, even though he isn't near that point yet, but I don't think that aggressively screaming at a kid that he has to eat less is doing any good. I can already imagine him refusing to finish his dish and her getting angry about it and not caring if it's her fault.