I’m sorry you have to deal with this.
My family is also like this.
They actually made me weigh myself in front of everyone as they had collectively decided that I can’t weight any more than 7st the way I look (I weight 9 1/2)
Remember, at the end of the day, only a health professional can tell you whether you’re in a healthy range or not.
I have firmly gone down the ‘comments like this is why people get eating disorders’ and ‘do you know it’s rude to comment on people’s bodies? But while we are here, would you like my detailed opinion on yours? I’d provide comments on what food you had, but unfortunately I didn’t pay attention to what you were eating as I have more important topics to think about’. Also ‘why are you so obsessed with women’s bodies? Do you think this is the most important thing of value about someone?’ Also ‘would you like my GP’s contact details to discuss this? Maybe they can give you some advice as they keep commenting about my excellent health’
Funny enough these kinds of comments have actually led for the offending party to more or less break down and confess about their own fears, insecurities, eating disorders and how people are on their case about their weight/ shape.
And we come to an agreement where the topic is off the table and that actually these kinds of comments should not be made by anyone, ever.
Unfortunately your sister and others alike are projecting their own insecurities onto you. Considering she decided to be frank with you, I’d be frank back if it happened again and said that she needs to stop and instead tackle whatever is going on in her life.
Please keep running and eating salmon. As a society we have lost sight of what’s normal.
It’s the eating crisps on the sofa all night lifestyle that is ‘concerning behaviour’ as many of us can testify.