Joan is a 17 year old who normally weighs 45 Kg She has lost 9 kg over past 3 months and has amenorrhea; Joan expresses an intense fear of gaining weight and is preoccupied with food. She is admitted with a diagnosis of anorexia nervosa. Joan's lunch consists of a small salad, a dinner roll and a bowl of soup and tea. What it is the responsibility of the nurse in order to assess intake?