To get rid of my IBS, I fasted for 3 days on homemade chicken broth (great for digestion) and some fermented Kvass. I don't think I would do it again, unless my IBS came back.

I know many, including Robb Wolf, suggest only fast for 16 hours.

I have done several fasts over the years. Two were for five days, to see if I could identify food allergies - the idea is that you stop eating (only drink water) for a day or two after your digestive system is cleaned of all food particles. Unfortunately, neither identified any allergies; but some allergies have threshold points - you need to need XXX grams before a reaction happens.

My longest fast was 16 days, as part of a spiritual pursuit - unfortunately I did not have any spiritual insights. Unless you consider becoming massively aware of how much time we spend on food - deciding what to buy, going to the shops to buy it, taking it home, cleaning it (if required), storing it, preparing it, eating it, cleaning up. I felt like had HOURS more time each day. I also lost a fair bit of weight.

I also found (as I was told and read about) that after two or three days (at most three), I experienced no hunger at all (and this is common). So, for 14 days, I was not hungry, although all I consumed was water.

As part of my religious upbringing, I performed many fasts as well. 4 days for Hanblaceya and 4 days for Wiwayang Wacipi. A few times, one lead into another for 8 days total. My Uncle has gone 18 days. For myself, I perform a 7-day cleanse once a year and frequent IF. It is true as Terrence said, after a few days you no longer experience hunger. Terrence, may I humbly suggest that sometimes no answer IS an answer?

9 days...........

I've done a few fasts over the past 3 years. the longest one being 18 days, mostly for spiritual reasons. I like how Terrence put it up above... you realize how much time goes into eating. days seem to go on forever. when i start eating again after a fast i appreciate the food so much more. i become very mindful of each bite. the texture. the flavor. the smell...

2 weeks I believe was the longest I went, only drinking water and having one meal a day. not sure if that counts as a fast though if you have random foods. I think with fasting its a specialized meal like chicken broth or cayenne pepper and lemon water.

I do this once or twice a year, fasting usually for 10-14 days. The first time was to finally rid myself of a persistent ulcer (which worked). Understanding that the concept of a "cleanse" has come under considerable ridicule lately, it's still part of why I do it. I've seen other benefits as well: improved vision, lost an allergy once and for all, reset my still slightly broken attitude towards eating, lost a pesky vanity pound or three around the middle, which stayed off.

I generally do it in the spring, maybe again in the fall if it feels right. Last year I didn't do it at all.

I just finished a 16 day fast a couple of days ago! Just to test myself, reset my eating habits (I decided to go paleo after the fast!) and learn about my hunger and cravings to better control them :)

I've done 10-15 fasts, starting in my teens. I'm now 55. My longest was 17 day, last summer, water only. It was very easy. I hardly notice the first 3 days now. I only broke it because I developed about 7 boils on my back (as part of the purification process). Otherwise I was doing fine, but those started to weaken me too much. After that I had improvement in my lungs (I tend toward bronchitis) and noticeable improvement in an "enlarged prostate" problem I've had for years.

I'm just ending the 5th day of a new fast (March 2012) and I'm not particularly weak but feeling the "austerity," detachment and freedom of the fast which is the best part. I hope to go at least 2 weeks or past those 17 days.

I do it for prayer reasons, to get prayers answered and improve my karma in general. (Both objectives are always fulfilled for me by fasting.) You also get visionary dreams, psychic enlargement, visions, and spiritual knowledge from it. Presently I am smelling divine smells. (Smells like unidentifable food combined with incense-like smells, like camphor, peppermint -- bewitchingly pleasant smells. They constantly change.) I always smell them now, but they are stronger during this fast. These are explained in the The Yoga Sutra and come from meditating on God and getting the reduction in body-attachment that fasting gives.

I started fasting in my teens and it has reduced my need for food during normal times. Normally I only eat one meal a day, after 5 pm, and it's not even a full meal, then some snackies in the evening. I've been like that for years. My main reason for fasting is to get to know God, make Him notice and answer prayers, improve my health, and save my people. All White men should fast. The "first activity of yoga" according to the Yoga-Sutra, basis of Christianity, is "austerities." Fasting, meditation and chastity are the highest and most effective austerities.

Aum, Amen.

No offense, but the idea of not eating for that long sounds dreadful. I'm already thin, I'd probably waste away. I went 3 weeks one time, but that was because of a ruptured appendix. I lost an impressive amount of weight, but I was also too weak to walk, it seemed like a poor tradeoff.

I'm currently practicing ADF (alternate day fasting) although I fast on M-W-F rather than true alternate days. I go about 42 hours of black coffee/water and by the time I eat a meal it's about 48 hours between solid foods.

I'm finding that's long enough to "feel" changes happening within the body. My body feels like it's working much better than before--much calmer. My skin and teeth are showing improvements, etc. I saw a table yesterday that said 24 hours won't produce a high level of ketones (I assume your true level will depend on your context and physiology) but by 48 hours you will have a high level of ketones.

I'm 2 weeks in and it's definitely been worthwhile but I'm not sure how long I'll continue with 3 days per week. I'm considering either shifting to 2 days per week or staying with 3 days but fasting only every other week.

EDIT: Ned Knock of Health Correlator provided a link to the table in a comment he made on Free the Animal.

I went 4 days once.

My last three days I've been OMAD - One Meal A Day... a 4pm dinner of about 1400cals. This is mostly because I've been working from home and very, very busy... my spare time was spent here on PH and other forums instead of cooking my meals.

Today I woke up and my wife shoved a plate of food in my face, salmon with cucumbers and leftover scotch eggs.

So I'm not fasting today.