So I have been keto-ing for about 2 months. I am down 16 or so pounds and feel good. Yay me. I have been reading about and considering fasting. I am a bored eater and I am trying to get out of the habit. I’m not hungry…I’m bored. The question:
People talk about not getting enough fat and avoiding starvation or famine but isnt that a result of fasting? Just using logic…I am sure you science people can answer for me 
Lean people and people who are not yet fat-adapted both have trouble fasting, because they have no spare fat or cannot yet efficiently metabolize their spare fat, respectively.
There is a difference between fasting and restricting calories. As Dr. Fung explains it, when we restrict our caloric intake, the body has to adapt to the lower amount of energy coming in, and it does so by slowing down the metabolic rate, putting non-essential processes on hold, etc. When we fast, however, the body simply shifts into full fat-burning mode, with no restriction on metabolism.
The evolutionary explanation is that the body interprets fasting as a period of interrupted abundance, meaning “time to go get more food,” so we need our energy. On the other hand, it interprets caloric restriction as lack of abundance—i.e., “there is not enough food to be had”—and hunkers down. The idea is that we can get through a famine by postponing reproduction, etc., until conditions become favorable again, but fasting simply means “out of food,” not “no food to be had.”
Yes, eventually not eating any food at all leads to starvation, but we can go for quite some time before starving. Fasting for too long has deleterious effects, but a week or so is usually fine, especially if we have excess fat to burn off. Both Dr. Fung and Dr. Phinney warn against extended fasting, because it can damage muscles.
I really appreciate this! Thank you! I get it now…I think:) I have plenty of extra fat to burn. I think i could live off my own body for a while.