The phrase 'You Are What You Eat' means that it is important to eat good food in order to be healthy and fit.
Example of Use: “I’m feeling more energetic now that I’ve started eating more salad.” Answer: “You are what you eat!”
The first mention of the phrase 'you are what you eat' came from the 1826 work Physiologie du Gout, ou Medetations de Gastronomie Transcendante, in which French author Anthelme Brillat-Savarin wrote: “Tell me what you eat and I will tell you what your are.”