Jane Fonda and Bulimia

Can someone tell me why Jane Fonda, one of Hollywood's most powerful actresses, formerly a feminist torch-bearer, utters a line about her son prefering thin women in her latest movie? The "humorous" line is delivered by an acid-tongued mother (Fonda) to her future daughter-in-law (played by Jennifer Lopez).

This, from a woman who suffered from severe bulimia for 25 years.

Why?