I do a 16 hour fast nearly every day, with an 8 hour feeding window, between noon and 8 pm usually. I've been doing this for several months. Right when I get up (between 7 and 9) I feel quite hungry, but after I have my coffee (within 1/2 hour of waking) I'm no longer hungry for a few hours, although my energy decreases as noon approaches. Is this an unnatural way to go about fasting? I enjoy the 8 hour window because if I have breakfast I want to keep eating shortly thereafter which is annoying and distracting. What would the effects be of stopping the daily fast?
Sounds like the Leangains approach. According to Berkhan, coffee will not interrupt your fasting state, so if it doesn't give you craptastic anxiety like it does me, then drink up. He recommends a 14/10 fast/feed ration for females, for some physiological reason that I can't remember, and also finds that he gets better compliance that way (which would make sense since there seems to be a biological basis for that recommendation). You said you start to lose energy by 12. Maybe the 14/10 approach would help?
Black coffee is a fine way to start an IF day, as it's a calorieless energy bump that supresses the appetite. Even with heavy cream, the lack of carbohydrate should at least mitigate the calories involved.
If your body is used to the extended fast, stopping it might have an effect on your set point. However, most IFers tend to do it randomly or sporadically, so as to keep the body guessing, and the fat release and metabolism pathways primed.
I used to regularly skip breakfast out of laziness, disorganization, w/e -- and pre-paleo, if I did have breakfast, thinking I was being healthy -- eat some plain oatmeal, "jump-start that metabolism!" -- I would experience the same hunger surges. Likely part of it was due to my metabolism activating after eating, but I do think it was also due to what I was eating.
Since starting paleo, I notice that I rarely have hunger pangs or even the urge to snack. I'm convinced it's largely due to better nourishment in general -- giving up grains has likely improved my digestive system's ability to extract nutrients from the food that I do eat, and steady consumption of good fat keeps me satiated longer. So, it may have something to do with what you're eating. (What are you eating?)
In general, I've heard that intermittent fasting can be a good thing. Like everything else, though, I would think that changing things up is a key factor. Otherwise, just like exercise, our bodies "figure out" the patterns, and then compensate for it in counter-productive ways (storing instead of burning fat, for example). Is there a reason you consistently limit your "feeding window"?
Hope that helps!
Just this past couple days I did a fast and coffee was definitely involved.
I had my last protein/fat meal at 8pm, slept, and around 12:30 had a cup of coffee with about 2 tsp half-and-half.
An hour or so after the coffee, I definitely felt the low-blood sugar hunger pains, but didn't eat anything and after about an hour or so it passed.
I ate a full meal around 5pm to break the fast and ate again at 9pm.
The only time I experienced hunger was after the coffee, which, I am assuming, is due to the blood sugar destabilizing effects of caffeine.
Since I didn't take in any food, however, my body eventually gave up trying to get me to eat sugar and went back to burning fat.