expression, noun
thin person who eats a lot; big eater who stays thin
Describes someone who remains slim despite eating large amounts. Often used with a sense of surprise or admiration.
彼女は痩せの大食いで、いつも大盛りを頼む。
She's a big eater who stays thin, and always orders a large portion.
あの人は痩せの大食いだから、いくら食べても太らない。
That person is a thin big eater, so no matter how much they eat, they don't gain weight.
A set phrase combining 痩せ (thinness) and 大食い (big eater). The exact origin is uncertain, but it likely arose from the common observation that some thin people eat surprisingly large amounts.