When I did it I went into withdrawal. Headaches, brain fog, etc. Once that passed my blood pressure dropped profoundly, my energy went up and I lost 60lbs without trying.  My bloodwork numbers improved dramatically, particularly blood sugar, a1c and the like. 

Refined sugars and other carbohydrates especially grains were not part of the diet of humans for many years. What our generation eats is unlike anything generations prior to WWII ever ate.