Noticed that too: a couple of insanely hungry days or brief periods of intense hunger pangs in the gut before losing. A body fights using its fat stores -- it's like savings in your bank account
Usually when the hunger pains hit me and my energy wains I take a nap if possible, then eat soon after. Also more water, fat and salt can help. I prefer some Topo-Chico sparkling mineral water to banish cravings.