you've just learned a great lesson! If you start on sugar mid-day (or worse, in the morning), your blood sugar starts that roller coaster ride. That we continue to eat sugar all day long does not mean we are weak...it's a physiological process! When I just can't resist a cheat, I almost always force myself to do it last thing in the day, after a regular LC meal. Either the urge dissipates before I get there, or if I succumb, at least I wake up in the morning without cravings, eat a protein-rich breakfast, and the cravings the rest of that day are minimal.

Life is learning. Rather than feel bad, try to be amazed at the clear bit of education you just got!