a question asked of me anonymously via sarahah: "Is it, or under what circumstances is it, fatphobic to congratulate someone on weight loss?"
Yes, it is always fatphobic to "congratulate" someone on weight loss or more accurately, size loss. First, it is never appropriate to comment on someone's bodily changes unless they have commented on it to you in a way that communicates their feelings about it and opens the space for you to comment also. Don't assume that anyone decreased in size on purpose. Don't assume that anyone is happy about decreasing in size. Don't assume that it is okay for you to comment on someone's body.
If someone tells you about their size loss in a way that shows they did it on purpose and they are happy about it, it is appropriate to make a positive comment. You can say something like "I am so happy you feel more comfortable in your skin now" or to express happiness for them about the positive causes or effects of this size loss. This is simply emphathizing with their feelings and there is nothing wrong with it.
Congratulating them, on the other hand, implies [all kinds of fat-phobic bullshit]
--- CN: fat-phobic ideas, this paragraph ---
that size loss is inherently a positive*, admirable* experience achievable* through hard work and perseverance, which is wrong, wrong, and WRONG. When people use nutrient-poor restrictive diets to lose size, this almost always causes health problems: this is not positive, even if they get the look they want for a short time. As for admirable, it is no more admirable than buying a new outfit. Changing your look is a personal decision and just like you wouldn't say congratulations if someone got a new haircut, you don't say congratulations when someone loses size.
--- end CN ---
Most of the factors that determine size are out of the control of a person, and size loss is mostly an accident or a fluke. Your body will return to what it is genetically comfortable with. Many people can achieve some form of athleticism but that does not usually mean a great size change. Fat bodies can be very athletic just as thin bodies can be very un-athletic, and your body thickness is almost as genetically determined as your height. Is it appropriate to congratulate someone for growing taller? no, because it is not an achievement. Size loss is not an achievement, it is merely a change.