I don't believe @jmcbn meant the snacking was causing the headaches, but rather the Larabar and it's sugar content (albeit natural sugar).
I have only been on this lifestyle shift for a few days, and am getting headaches myself. However, I do believe in the message behind this cleanse; sometimes your body needs a shock to remind it that it is not functioning at the optimum setting. If you drown yourself in sugar and carby grease (as DELICIOUS as it is), your brain can't remember what it did before all that.
Whole30 cannot be considered a fad diet, in my opinion, because it's not a diet. We are not meant to complete the 30 days and jump right back into our old habits... that would be counter productive. Whole30 is supposed to help you become present within your relationship with food, and allow you to start fresh with it for a brighter, healthier future. Fad diets are for people who want a quick fix with very little permanency.