72 hours, give or take, after a man stops consuming food of any kind (48 hours for a woman), he enters a state of ketosis. The liver exhausts its supply of glycogen (stored glucose), which triggers the breakdown of fat into keytones. These keytones are the body’s only fuel during ketosis. The digestive system shuts down and hunger disappears entirely.
Sounds terrible, doesn’t it? But it isn’t.

Digestion requires a great deal of energy. During ketosis, that energy is diverted to cleansing and repair. Side effects of ketosis can be increased alertness and increased capacity for activity. (And, of course, weight loss, for those who want to lose weight.) It’s a natural, healthy state rarely experienced by modern consumers of high-carb diets, but quite familiar to our hunter-gatherer ancestors. The simple fact is that we’ve evolved to function as hybrid fuel vehicles, metabolising carbohydrates during times of plenty, and fat reserves during times of scarcity. Not for just hours or days, mind you, but for weeks and months.

On Monday at 8:30 a.m., I drank my last glass of juice (carrot apple). That was exactly 72 hours ago. I’m still a little hungry, but considerably less so than I was at the 24 or 48 hour marks. My energy is undiminished.

I plan to continue the water fast until my body tells me to stop, which it will do by signaling hunger again. The signal will be clear — what’s called “true hunger,” as opposed to the minor discomfort we feel (and I’m sort of feeling now) when the pizza delivery guy gets held up in traffic. True hunger is what precedes starvation.
I’m fortunate in that I don’t drink or smoke. If I did, the last few days would have been very difficult, indeed.