My Mom’s Boyfriend Just Told Her That He Doesn’t Want A 400 Pound Woman

i female (18) and my mom (45), and her bf (idk his exact age) all live together. i had just finished christmas shopping for him and decided to why not get some food for us so my mom doesn’t have to cook. now mind you my mom has health issues with her body keep this in mind. i ordered a pizza and gave her one slice because it’s all she wanted, now after we ate a few hours went by and she started having stomach aches and her bf starts yelling at her saying she shouldn’t have ate it. basically saying she didn’t give a damn about her weight when my mom is literally having back to back operations and is now fully recovering from one so she has not been able to exercise or anything for awhile. then my mom tried to explain to him she is not in a position to work out at the moment, but then he shouts that he doesn’t want a 400 pound woman and needed a better diet when my mom hardly eats much as it is. i am waiting until he leaves tomorrow morning to talk to her about this because he’s always making snarky remarks towards us and i am getting fed up and i want to know how to go about it…please help any advice would be helpful!!