I Struggle With My Body Image

I have a friend who has decided to go on the Keto diet because she hates her body. While I know this can be an effective way to lose weight, I also have heard that it can quickly become malnourishment and unhealthy so how do I go about talking to her about these things? I have also struggled with body image, but I never know what to say to others who struggle with it as well because let's be honest, 100 people can tell us we're "beautiful" and "fine just the way we are" but that doesn't really do anything, even if they mean it...