What does it mean to be " thin on the outside, fat on the inside " ?

On the outside you may appear slim, but what you put into your body are things that potentially make you fat.

Kinda like someone who eats unhealthy but doesnt gain weight.

Hope this helps Buddy!

- Courtney

Is this an English question, like figurative language, or are you referring to TOFI, a term used to describe lean individuals with a disproportionate amount of fat (adipose tissue) stored in their abdomen?

um, what am i suppose to answer here? it just said that he will studied hared because of a grade in spanish.