It is a very eye-opening experience for them to see in numbers what they are actually eating. Based on the typical 2000 calorie per day diet, I have some kids who should have had massive heart attacks by the age of 12, and some who put my diet to shame. This should not be a plan for one day but for an entire week. That way they see it is possible to have a larger meal one day and balance it out with smaller ones on other days. I try to include a test question for this unit which shows the food a typical person eats in a three day period and ask the students to tell me what is wrong with the diet.
Answers can be varied and sometimes very interesting.
I see this exercise as a great example of how chemistry classes can be integrated with biology, health, and biochemistry as well as many other subjects.