Sizeism: discrimination or prejudice directed against people because of their size and especially because of their weight
-- https://www.merriam-webster.com/dictionary/sizeism
Fatphobia: irrational fear of, aversion to, or discrimination against obesity or people with obesity
--https://www.collinsdictionary.com/us/submission/21048/fatphobia
Fat Liberation: A social movement seeking to change anti-fat bias in social attitudes by raising awareness among the general public about the obstacles faced by fat people experiencing the stigma of obesity.
-- https://en.wikipedia.org/wiki/Fat_acceptance_movement