Has anyone experimented with slightly longer fasts? I've been doing the normal Eat-Stop-Eat style fasts for a while, and liking them. I keep meaning to do a two day fast or longer, just to see the effect. I'm not talking about fasting for the sake of fasting or really long fasts, but somewhere in the order of 2 or 3 days maximum. I would appreciate any interesting experiences people have had, or links to any studies.
I fast between ~8-9pm to ~6-7pm the next day, every day, since a few months back. Nice not to have to think about lunch boxes, snacks, breakfast and whatnot, and it saves time.
I've fasted for up to 30 days. The problem with a three-day fast is that for most people, the first three days are likely to be unpleasant. (It depends on how keto-adapted they are beforehand.) If they continued past three days, the fast would get easier.
My experience on a longer fast was that from day four to the end of the second week, I felt normal. I wasn't hungry. Most of the time I couldn't even tell I was fasting. The body is adapted to long (several week) fasts. It's part of our evolutionary experience.
The first few days may feel bad and (depending on the person's glycogen stores) induce a lot of water loss. This frightens people. They think a longer fast would be the same, but it wouldn't.
It takes longer for the body to switch over to "fasting mode" than most people realize. The brain takes two weeks to fully switch over to using ketones. It's the brain's demands for glucose -- which gradually diminish as the brain switches over to ketones -- that make people feel bad when they begin fasting. People think they are "in ketosis" within a day. Actually ketosis is a matter of degree, and it takes about four weeks of continuous, complete fasting for the body to maximize its use of ketones.
I don't want to discourage you, but I have to say, based on my experiences, there is nothing particularly interesting about fasting for three days. I'm skeptical that it has much of a benefit. I know it seems like a long fast to people, but really, it's a short fast. The body hardly begins to switch over to "fasting mode" in that length of time.
Probably everybody here has fasted for three days at some point in their lives when they got sick. When people get the flu, they often fast for about five days. It's really not a big deal.
Thomas Seyfried, a biochemist who studies fasting as a treatment for cancer, thinks that a fast of seven to ten days is useful for preventing cancer. He bases this on experiments with rodents and levels of induced ketosis. If somebody is considering a fast for therapeutic reasons, Seyfried's seven-to-ten days might be a good minimum.
You asked for links to studies. There are hundreds of studies about fasting. I'll give you three to get you started.
Here's a good overall review article about fasting:
Here's an article about the longest fast in the medical literature. This guy fasted for 382 days. I cite this article to establish some perspective about "long" and "short" fasts:
Here's a review article by George Cahill who was one of the scientists who discovered the purpose of ketosis in the 1960s.
It's been several years, but I've fasted up to 6 days for religious reasons. I was tired the first few days, but after that I felt great. This was when I was still eating the standard Amerian diet, and even then, hunger went away after a few days. You may notice a smaller appetite after a longer fast. Eat small, easily digestible meals at first.
Longest for me is a three-day fast. First day was annoying due to hunger pangs; I kept walking towards the refrigerator. On the second day the hunger was absent but I got kind of twitchy; couldn't settle down. Third day was cool. I was going to do another couple of days but I had a dinner party to attend that night.
It is amazing the amount of time one gains by not having to prepare a meal or do the clean-up afterwards.
My Best experience to date is with smaller Fast of 12 to 16 hours. With a Paleo nutrition plan properly dial in and blood sugar stable, fasting is easy and liberating. More then that, from what I heard from Mat Lalonde and Robb Wolf, the stress created on your body counter balance the beneficial aspect of the fast.
My 2 rocks
Longest fast I've done is about 3 days. After the first day I didn't feel hungry at all, only ate because convention dictated I should. Hunger pangs on first day, but then if you're used to fasting you'll be used to these, then didn't really notice except for the fact that my day was longer due to not having to stop to eat. Don't recall any real effects though - positive or negative.
Be careful. I've fasted for a week or more at a time several times. It feels great at the time but the stress can have a significant, negative and long-term impact on your adrenals, thyroid, etc. Personally I wouldn't want to go more than 24-36 hours now.
Not really the same, but I got food poisoning once and couldn't eat for about a week afterwards. Just some pedialite/gatorade type stuff after a couple days. I lost like 8 pounds and was super weak when I went back to the gym. Took about a month to get back up to my old strength.
Knowing this experience I wouldn't give up protein for more than a few days.
I tried 3 days and was fine. I was trying to fix candida overgrowth problems. When I started eating again, I was feeling better, but it was just temporary and the candida problems came back very fast.
I think that when you don't go to the real source of a problem, other treatments just patch the real problem.
I find it really surprising some people fast for like 2 weeks. I personally think this is dangerous, but people following those approaches are so sure of themselves, it's like a religion. They are often the same who eat only raw fruits and vegetables and who do constant colon cleanses. Way to go the unnatural way! I have difficulty imagining caveman doing colon cleanses.
The longest fast I have done was two days. This was unintentional, as I ate a huge meal for dinner one night and just was not hungry until two days later. I don't recommend fasting for more than a day if you are trying to maintain or gain weight. I killed my metabolism and lost a fair amount of weight (when I had none to lose) trying to fast during last summer because I couldn't make up the caloric difference in the one big meal; been correcting it ever since.