How do you deal with people who kept calling themselves fat when they are incredibly thin?

Anonymous
Hi. I have had many friends and acquaintances who kept complaining that their fat and heavy everyday and almost every time. I know most people would suggest that I ignore them, or I just let them be. But sometimes, I can't help but feeling unhappy with it and feel that they are very inconsiderate with my feelings. Allow me to explain why:

I've been chubby/slightly on the heavier side due to medical conditions since young. I've been trying my best to stay healthy (though I'm still not slim nor thin) and I exercise (I can't do that much or be intense due to medical conditions). I feel slightly hurt, unhappy or feel that inconsiderate for them to keep saying their fat in front of me, especially when looking at their photos with me (I'm clearly the fattest in the bunch), when they weigh about 90lbs or below for 5'2 or 5'3 and that they are perfectly fine, healthy and look great and have had many guys after them (whilst I don't).

I have politely told them that they are not fat, and I mean what I say. Still, they don't stop it and they kept going on diet for say a month or so and go into such habits. What should I do? And has anyone felt the way that I do? :'(

PS: I also hope some users here would be careful with their words because saying things like what my friends say can be very inconsiderate and hurt other people's feelings.
Updates
+1 y
Forgot to add: I don't comment or say anything about people who are thin or fat because I understand people may get upset due to certain past or conditions that they are facing, psychologically, mentally or physically
How do you deal with people who kept calling themselves fat when they are incredibly thin?
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