This challenge will be harder than you think!
Complete this challenge everyday this week.
Keep a food diary every day this week. Include all of your snacks, meals (and cheats!). It can be a good idea to include your sleep and energy levels as well. Sometime we can feel 'sluggish' after eating certain foods so the more information you can gather the better you can interpret how your body functions with the fuel you provide it with.
There are lots of good apps that you can use (I like MyFitnessPal) but a good old' pen and paper works too!