“Skinny” (瘦) is clearly written with a sickness radical (病字旁): 疒.
Outlier, also, writes the following in its definition:
瘦 shòu is composed of 叟 sǒu and 疒 “to be sick, not well,” pointing to the original meaning “to have little muscle or fat; to be skinny.” 叟 gives the sound.
What sickness was 瘦 actually referring to though? Or is it simply that all these people vying to loose weight just can't wait to be “ill”?