It's plain jealousy and sabotage. They see a beautiful woman they envy and who reminds them of everything they aren't, and it drives them nuts. So they only tell her negative things/criticisms, because they hope to beat down her weight accomplishments. She reminds them of their own failures and lack of control in everyday living/eating. As a normal size woman it is always expected to hear "you should eat more" comments come out of the mouths of women fatter than you. I hear this all the time from fat women, but rarely if ever from fit/normal sized women.