Up to two weeks at a time of a total (water only) fast? I've done this before, but it was quite difficult to maintain in the midst of work pressures and I'm curious to know how you manage it.
I'm very interested in this. I've never tried fasting before -- and I'm 33 years old, which means I've had a lot of time to get used to eating a lot -- so I imagine that I would have a feeling of "starvation" that would be awfully distracting. Plus, I'm a bear when I'm too hungry and I wonder what I could do to avoid taking it out on the people who surround me (especially my 5 year-old kid).
I find that passes, as long as I've slept well, drunk enough (water) and am otherwise feeling fine.
I often go all day without eating while I work, and contrary to the OP and more in line with several of the other posters here I do find myself more productive, able to concentrate and focus, and feeling more energetic (I know it's counter-intuitive).
However the slightest inkling that I'm feeling worse for it, or that my productivity is beginning to slip, I'm feeling unusually tired - I'll simply eat. I'm not entirely sure losing much weight would be good for me (I don't have much to lose) and I'm not trying to take things to extremes. I just side with folk who agree that 3+ regular meals a day is not necessarily the only healthy way to do things.
Note well that this is all simply my own experience, and I'm certain people differ. I do this because I'm happy, comfortable and feel better for doing so - if you try it and don't, perhaps it isn't for you. I know I wouldn't do it if that were the case.
Drink lots of water. When you feel like you _must_ eat right now (rarely happens after day two), drink a liter of water, and go for a short 5 minute walk.
Also, add a few drops of freshly squeezed lemon juice to your water. The availability of flavor is often enough to get you through the hard 5 minutes (and after day two, it is rarely more than 5 minutes).
My experience is that even with lots of water you get serious muscle fatigue starting on day 4, and major dizzy spells everytime that you sit down/stand up. Also, the body seems to go into something of a hibernation mode and want more sleep. Besides those factors, I'd say I've managed reasonably well, and I think you could continue to work a desk job just fine -- but the inability to move quickly will kill any exercise patterns you have, or, potentially, the ability to do much more than 5 minute walks. It also makes it far more difficult to get out of bed in the morning.
Interesting. I guess it depends on the kind of exercise you do.
What I noticed is that around day 7 or so, anaerobic exercise (e.g., thai boxing) becomes very demanding and hard to keep up for more than a few minutes at a time. However, it's just as easy as always to do aerobic exercise like jogging or swimming.
Never had dizzy spells or feeling of muscle fatigue (except for anaerobic exercise) - and it was also easier to get out of bed in the morning.
However, a friend of mine noted that my body goes into a super-economic mode - that I hardly lift my feet off the ground when I walk (less than an inch on average), and that my arms seem to move quite a bit less.
I wonder if the insertion of lemon juice is enough to counterbalance the dizzy spells. I recall doing long walks but not any jogging while doing longer fasts.
I'm very surprised by the lack of muscle fatigue though. I've done fasts of 4+ days 10+ times and I always get significant muscle fatigue around that point (esp. in the hamstrings).
Very curious now what causes the dizzy spells. Please send me a github message or something if you ever find info. This is a long term interest of mine.
http://www.ayubmed.edu.pk/JAMC/PAST/21-4/Latifynia.pdf
An amusing book on complete fasting by vintage american novelist Upton Sinclair here:
http://archive.org/details/fastingcure00sinciala
Personally, I fast regularly up to two weeks at a time, both for weight control and because I believe in it's overall long term health benefits.