Mother in law keeps calling me fat

Nonsense.

@Zaina89 as a pp said, you are doing exactly the right thing getting your GPs advice. And it sounds like you are doing everything you can to live a healthy lifestyle.
Culture is one thing, but this rude woman is upsetting you on a daily basis for two months. Now she's starting on your poor DD at such a delicate stage in her life.
Your DH ought to tell her that the daily fat shaming has to stop immediately. It is abuse. It leads to eating disorders.
Ask him, Does he want your DD to go into school, look around her classroom and think "I am not worthy. I am the worst one here. No one can like me because of how I look, which is awful."
There's been lots of advice about being calm but assertive.
Have some phrases ready, which you deliver very sweetly, non emotionally but very firmly
Actually I would record some of her comments and play them back to DH since he is in convenient denial. He's just hoping you willl shut up about it and he won't have to do anything and he can continue the quiet life.

But you also need to look at how to protect yourself and DD more.
"today I asked her to alter some of my outfits and make them a bit bigger from the hips"
That's actually playing right into her hands. Stop offering polite conversation beyond the neutral, "Good Morning" "Cup of Tea." Weather ect. and don't give her further information on anything medical. She's not a doctor.
Hopefully her flight home is not that far away.

Actually I take this back. There's no need to harp on the appearance of teens, especially girls. Better to emphasise other things: sports, friends, hobbies, education, fun...

Stop accepting these comments. She is being rude - maybe not in her culture, but she is in yours.

The comments about your daughter I would be absolutely furious about - people have different body shapes and the pubertal transition is tricky in young girls without rude comments.

It doesn't matter that she doesn't think she's being hurtful - you need to be very clear to your husband that it IS hurtful and it must stop.

Make trouble, stick up for yourself, stick up for your child!

You get called fat once - maybe ask politely to not do it in your house, cultural differences etc so might not be obvious it’s hurtful

Twice - ask to stop it not so politely, reiterate why

Three times - stop engaging and wait for an apology

More - issue an ultimatum

instead:

months of putting up with this every day
crying in the bedroom
letting your daughter’s weight to be commented on
asking MIL to alter the clothes (??)
post on mumsnet to vent

….

You letting her say this to you and crying in private is one thing but you are letting your daughter down. Why isn't someone advocating for her because your husband sure as shit won't do it and upset mummy.

I'm so glad people are starting to point this out. I guess its hard to truly understand when you come from a country with no real culture like England and all of a sudden marry into a community with a rich and vibrant culture that has been shaped for hundreds/thousands of years. Hopefully the OP understands that these comments from the in-laws are not coming from a place of hate.

Ignore posters saying that you should talk about medical issues.

Ignore posters who suggest that you should tolerate comments you don't like for "cultural reasons."

Ignore the xenophobic comments about marrying into another culture.

If you are upset by the comments, regardless of intent, then they need to stop, and your DH needs to stop them.

I don’t think fat necessarily is always distributed evenly at all. Men tend to just get a stomach unless very very obese and most still keep slim legs. Women have different body shapes so while some will gain everywhere, pears will generally mostly gain around the hips/bum/thighs and apples around the middle. Apple shapes are interesting because those women can be huge on top with tiny stick legs.

Anyway, that aside. Your MIL needs to go in the bin.

Time to lose your temper. Volcanically. She’s allowed to say what she wants, so surely the same applies to you?
No guest would be rude about my young daughter’s body in my house without getting a very direct conversation in return.
Hold the line for your daughter even if you can’t do it for yourself.

Absolutely irrelevant, don’t be foolish.

I would say “if you say another nasty thing to me we’re going to have a serious falling out which would be very sad as it would mean you wouldn’t be able to visit again”

When I've been to east Asia, commenting on size isn't a faux pas like here. It's more like a matter of fact.
Could it be that your MIL doesn't realise she's upsetting you?

She sounds like an insensitive twat.
Find the strength to call her out for this nonsense in front of your daughter so your daughter can see how completely unacceptable commenting on people's bodies is.

As an aside - I know someone who began microdosing GLP1 meds for their lipoedema and it has been very helpful to them/improved their lower body symptoms a lot.

So, it would be fine for us to go to somewhere like Japan and do something repeatedly that everyone in Japan found offensive whilst we wittered 'it's okay in my culture'

No? Thought not.

If someone is visiting the UK and have family here they need to adapt to our cultural rules and norms - so not insulting people.

It does seem an Asian thing to comment on weight. My son is married to a Thai lady and all her friends and family call him the fat one!!

I admit it is horrible and your MIL needs to be told it isn't acceptable.

It’s a little different though because it is actively seen as rude in some cultures to ignore somebody’s obvious weight gain. Whereas in Britain ignoring it would be the polite thing to do, in some cultures it would be a sign you don’t care about them enough to notice small changes in their appearance. So her commenting on it is very much ingrained as the polite thing to do. So it’s a complete flip from British culture not just a small tweak, and will be difficult for her to adjust her behaviour.

She stays with you for up to a quarter of the year? She’s making these comments to you and your 11 year old.
You and DH have to sit her down and say it’s not acceptable. If she can’t stop making such comments she can’t come and stay. (Ultimately I would be restricting access to your child too.)

What?! Christ on a bike, what utter bloody nonsense is this now 🙄

Just because your relatives didn't have a happy relationship, does not mean 'it doesnt work'.

I'm of mixed descent. Lots of people are in happy mixed cultural relationships. Of course it can bloody work!

You need to make her leave. Actually, no. Your DH needs to. You're going to end up with absolutely no self esteem left at this rate.

In the meantime, when she says something so hurtful, maybe suggest she trims her nose hairs or perhaps an upper lip wax. She'll go in no time when it's dished back.

If it helps, probably won't, I've been housebound since December. My neighbours were all having a natter outside and I hadn't realised, I went to take some recycling out to the bin. My next door neighbour literally shouted in front of this group of women 'Lil, you've got so FAT!!'. I was lost for words so just went back indoors and, tbf, everyone else looked so embarrassed and shot off.

Why is this rude cow still staying with you? I don’t care if it’s her culture, it’s not acceptable and she’s been told this. And now she’s started on your DD? No way. She needs to go. Your DH needs to enforce this and stand up for you. If he doesn’t, he can go too. Don’t put up with this shit op.

At least now can we ignore this poster?

She needs stopping, this is awful
for you and damaging to your daughter.
Both you and your husband need to stop her every time very clearly

“Stop mentioning my body and weight - it’s rude”

“Any conversations about weight and shape are unacceptable”

”This subject is closed and off limits”

”MIL - stop!”

Does she know it’s a medical issue? Tell her - no need for details

”MIL - this is caused by a medical
issue under investigation and you are making it worse”

Seriously - call her out on it every time. What’s the worst that could happen?