Everyone has their philosophy on eating well. The interviewer simply wants to hear that you have a stance on what eating well means to you. You might mention that eating well means eating organic as often as possible. You might mention that grass-fed meats are your thing. You might share that eating fruits and vegetables regularly is a good idea. You might share that you really believe in eating local foods. Or, you might share that eating a well balanced diet full of different nutrients in your idea of eating well. Simply share your 'eating well' philosophy with the interviewer.