I don't think intermittent fasting will make your poo black. Black sticky poo can be from bleeding of the stomach or intestine. Black poo with a more normal texture can be from iron supplements, or other things you ate.
It's pretty easy to check for the presence of heme in stool - I think any primary care doctor can do it.
I have done a 23 day water fast and a 29 day water fast. Im an iron worker with a physical job and I put in lots of overtime. After the 4th day of fasting, its smooth sailing. Energy and mental clarity happens when you switch over into ketosis. Fasting is one of the best things I have ever discovered. I feel and sleep sooooo much better when Im not packing around extra weight (plus all the bennies that come with a long fast) Now I just do a 5 day every month (during one work week) Sometimes I skip a month. The only downside I noticed when fasting is getting lightheaded for a few secs if I stand up too fast.
I love eating keto but since the woman is always getting ahold of free sources of food and is always bring boxes of it home ..... its hard to eat that way. We have a very large supply of food that has to be rotated and used.
Location: Moved from south central WI to Portland, OR
It's interesting to me that you say it gets easier after the 4th day of fasting, but then you say that you are choosing to fast 5 days each month.
Sounds like maximal willpower required!
I still have not gone more than 2 days without eating. I've gained a few pounds over the holidays so I'm thinking I should do something. . . .
My work is not physically demanding but it is mentally demanding, so I've been nervous to try going days without eating while I'm working. On the other hand, it's much easier for me to fast on work days because I'm busy and away from food (other than the omnipresent candy and frequent treats - I'm doing pretty well with those).