How do you get past the brain fog during that period of time? My understanding is that your brain requires glucose, and that your liver will convert fat to glucose if absolutely necessary (such as when you're in ketosis), hence the "keto flu" transition phase.

From my own experience I would say the brain fog comes from being too much used to carbs.

Recently I started doing 72h salt-water only fasting once a month and my experience is that I get somewhat dizzy after 24h in the evening, but after a sleep I can perform normally without any need to eat, even including interval training and extreme uphill biking (slightly salty water is important here). This holds also for the 3rd day, again, absolutely no need to eat. Motivation were recent articles suggesting rejuvenation of one's immunity after 72h and subsequent feeding - will see if it works.

However, I believe I can do that only after I went on low-carb/no-carb diet for the past 2 years - I remember feeling horrible the first month on this diet with what you could name as "brain fog" most of the days - I guess at that point my body was learning how to survive on low carbs.

Anyway, fast forward, I am now far stronger, calmer (also due to 5 minute cold showers every day) and have brain clarity I haven't had in the past 10 years, which brings relax to what would most other people take as very stressful work, as the mind can perform and focus better and faster.

Your liver doesn't convert fat to glucose, it converts it to ketone bodies (such as acetone) which the body can also use for energy instead of glucose.

Whoops! You're right. I had thought I read somewhere the brain requires another organ to convert ketone bodies to glucose, but it appears its the liver itself at cannot use ketone bodies:

http://en.wikipedia.org/wiki/Ketone_bodies#Uses_in_the_heart...

Yeah, the liver has a separate metabolic pathway for converting non-carbohydrate organic compounds into glucose at a steady rate to regulate blood sugar and provide energy to the brain, it's called gluconeogenesis http://en.wikipedia.org/wiki/Gluconeogenesis

There are a lot of interesting things that happen while fasting, and I think we don't have nearly enough research on it. I'm far more interested in the possible beneficial effects at the level of the central nervous system - that's where I'd like most research to go.

>Actually there is a natural way to hack your body and increase your HGH by about 2000% [1] via fasting.

>One theory is that when you fast, your body activates the HGH to help burn fat at faster rate.

That somewhat dovetails with generally recommended practice of having only scheduled 3-4 meals during the day without snacking in-between and thus giving yourself an opportunity to get hungry in-between the meals vs. constant snacking (incl. sugary soft drinks drinking).

16-24h intermittent fasting for HGH, 72 hours for immunity refresh.

3-day fasting is brutal. I don't think most people can do it.

I speak as someone who has fasted up to 1 week. Interestingly, the difficult period is exactly the initial 2...3 days. After that it's no effort at all - albeit physical performance seems to decrease, of course.

You may well be right about most people, but in my experience it's not that hard. My wife and I have been fasting for 3 consecutive days each week for over a year (we worked up to it over the previous year). It's become pretty easy now. I rarely feel hunger.

BTW, I feel I must add (for the benefit of random readers stumbling upon this thread) that most people should not attempt long-duration fasting. It may not be beneficial at all, and there are certain dangers associated with it. Up to 3 days is probably okay if you're overall healthy, but most people should stop around this point (I can't draw a firm line as it's not an exact science). 1 week becomes pretty sketchy for everyone.

The human body could go on like that for a few weeks actually, but I don't think there are any benefits beyond 2...3...4 days [research needed], and the dangers multiply rapidly the more you push into very long durations.

Drink water with electrolytes during fasting, e.g. a little bit of salt. If you drink just normal water, it's hypotonic and you'll lose electrolytes, bringing you to a hangover-like state - that might be brutal then.

Depends on what you do while fasting. I couldn't fast one day under heavy mental activity. I feel nauseous when I'm deeply thinking while coding for too long without eating.

@bitL is correct. 48-74 hour fasting has shown to regenerate new immune cells [1]

Also as others have said it, you go over a bump and it becomes easy. Also, there is a window where I'm rather productive and less ADD when I'm fasting.

[1] http://www.medicalnewstoday.com/articles/277860.php

> there is a window where I'm rather productive and less ADD when I'm fasting.

Something happens to the brain during prolonged fasting (within reason), and it's something that seems pretty darn good overall.

If you practice meditation, fasting seems to help a lot.

There are benefits to fasting for 10 hours: http://www.sciencealert.com/new-research-suggests-you-make-b...

The research was also summarized as "always gamble on an empty stomach."

And a better article about the study: https://news.usc.edu/63669/fasting-triggers-stem-cell-regene...

The published paper: http://www.cell.com/cell-stem-cell/abstract/S1934-5909(14)00...

I've been told by the medical that fasting might get you stomach ulcers from the acidity.

What is the frequency of those fasts? Every week?

I guess that's individual, you have to find what works for you. Some pro athletes I know (triathlon) do intermittent fasting twice a week and do strength training right after. I guess in the beginning once 1-2 weeks should get you started.

I presume you'd have to get to fit form first?

I do it once a week...Usually starting on Wednesday (I'm starting again now) and either go till Thursday or Friday. Actually there are times I'm less ADD and a lot more productive.

I stopped doing them, but I noticed that for me fasting for 16 hours is pretty easy, much easier than doing portion control of very tasty things that appear in front of me...