Tired of my families making fun of me being "fat" or how I eat

So one part of my family is Germans. They're family orientated and helped me out a lot throughy teenage years. One thing that has been bothering me a lot is how often they judges what I eat, how much spices I put on my food and constantly just trying to make jokes about me being fat.

FYI, I'm a 25 years old Thai woman, weight 49kg and 160cm. Medically I'm healthy and living in Europe, I'm considered petite. While my germans family on the otherhand, they're fat. I understand it's their genetics to have bigger figures since they're Germans but they're just genuinely fat and being close to obesity. Even with their tall height couldn't help them hide their unhealthy weights. They couldn't walk without running out of breath and struggles to just sit down or get up.

So I don't understand why they fun of me so much. It's not just me, my ex and my current boyfriend also experienced the same issue when they met my family. They've complained to me how my family is full of dramas, judgemental and the audacity to make fun of our appearance when they look like that. Both my and my boyfriend are natural skinny men due to fast metabolism so it doesn't make sense why they think it's okay to make fun of people who's much skinnier than they are.

All my German family ever eat is breads, cheese and cold meats. They eat so little during lunch and dinner but snacks through the day. There's barely any flavour in their food as well but I still ate it anyways due to respect and adaptation. Most of the time I eat my mom's cooking at home(Thai food) after I eat at my grandparent's food(german food) to feel full and go on about my days. I love chips so I tend to stock them up a lot in my room just because I like the aesthetic of having a cool cabinet area that looks like a convenience store. However, I don't eat them all in one go, I takes me about 2 months finish them all because I take only about 2-3 bites a day and put them away.

I don't believe it's out of jealousy since they've been good to me in every other aspect and I can't see them as bullies except for this matter. I just wonder if they're trying to show that they're the dominant ones in the family because me and my mom are Asians. I've seen my granpa screamed at my mom's just simply because my mom couldn't understand what was going on or didn't hear what they say to her properly. It has been getting worse as years goes by... the family that used to be so kind and loving to me have changed so much and I really couldn't stand what changed them except for their weights that kept going up.