First of all, I have a vague suspicion that RV and I couldn’t survive being locked in the same room together for prolonged periods, there was even some minor polite friction between us some time back. So please do stop calling us alter-egos and such. More like siblings in a very competitive family (which is merely a description and no indication about SubClub as a family). He’s still my bro. 
Moving on…
Fasting. I try to do a month of water-fasting every year when the weather picks up (gets quite cold when the internal oven shuts down). Like a spring cleanup. I also fast one day a week on my stretch day. My longest on water was about two months, on juice 4 months and on nothing but air about 5 days.
I wrote a massive monologue, but just in case you’d just want something brief: If you do 10 days, you should barely notice a thing. Day 3 and possibly 4 will be tough, be prepared to lie in bed or stay on the couch all day. This is the body switching to full ketosis and that switch leaves you without energy. You may also experience some lower back pain or headache, which is similar to reconciliation, just let it happen.
When re-feeding, start with fruit juices (swish them around in your mouth a bit before swallowing), then vegetable juices, then solid fruits and vegetables, then rice/potatoes and similar easy carbs and finally whatever you normally eat. Aim for the process taking about half the time of your fast.
With a shorter fast there shouldn’t be any adverse side-effects if you give in to the temptation sooner, but you might be disappointed in yourself. Re-feeding the right way allows the body to re-stock on water-weight necessary for digestion and get the engine running again. This prevents feeling bloated, sluggish or getting headaches.
And for those interested:
TL;DR
The body taps into its reserves and should have enough to handle a month of being without food without any real effects. That’s a survival mechanism we are all born with, the body stores what it needs in case we get lost somewhere.
In my experience (and that of researchers having done all kinds of research into fasting for its ability to cure stubborn diseases including the big C), a human body on a healthy diet can go up to 60 days on nothing but water in an area with temperate atmospheric conditions. However, 30 days is the “healthy” cut-off point. After that, one should be careful.
The key-words here being “healthy diet” The body stores a supply of what it needs around the organs and in the fat cells for a rainy day. This mechanism isn’t fully equipped to deal with an imbalanced amount of vitamins and minerals so it doesn’t realize it can run out of one thing while it still has enough of the others. That can be dangerous. I have experienced re-feeding syndrome (otherwise known as a serious electrolyte shortage) and it is no fun. Fortunately for me it manifests only as swollen ankles and feet and weird sleeping.
The body also stores all bad stuff it wasn’t able to digest between meals in the fat cells. It’s a back-log that gets processed while you fast, leading to what is commonly called a detox-crisis. Headaches and lower back pains are common as organs like the kidneys get to work overtime. This is like reconciliation, it comes in cycles. Just stay the course and it will end with you feeling better than before.
That said, with 10-14 days for a person that has been eating reasonably healthy it should be barely noticeable. You’ll get a bit a muscle loss in the beginning (comes back fast after), feel really crappy on day 3 or 4, and get some cramping and cravings occasionally. There should be no health risks at all.
When it comes to re-feeding, the general recommendation is to start with fruit juices, then vegetable juices, then solid fruits, followed by vegetables and then carbs like rice or potatoes. Start with the things that are “light” on the digestion and slowly move up the scale, saving the meat for last.
Generally I’d say to make the re-feeding process about half the time as the fast itself. Give your body time to replenish the water weight needed for digestion. Also, make sure to take some probiotics when you get back to eating, especially if you’re not a vegan. The body loses some of its digestive bacteria, they could use some help re-colonizing faster.
I’ll admit I’ve seldom managed to do the re-feeding right. Once I start eating it’s just so yummy, all those flavor explosions and energy surges. For most people the worst that happens is a bloated feeling, sluggishness and maybe a headache, no big adverse effects. Be mindful not to eat too much though. Start exercising and portion your caloric intake accordingly. Especially if you also wanted to lose some weight in addition to the health benefits.
On the contrary to common magazine stories, the metabolism actually doesn’t come to a crashing halt right away since most of it is still tied to the muscles. It goes down very gradually. Especially if you still keep using your muscles.
If you’re taking any medication, be mindful. Especially with blood-regulating medication (or insulin-regulating ones). The body will attempt to reset these things by itself and the medication may lead to a hospital visit. Your internal body temperature drops when the digestive oven goes into maintenance mode. Around the second week or so the blood pressure and heart rate start dropping leading to the common pale skin and friends asking if you’re okay even though you feel like you can take on the world. Also means you can no longer jump out of bed in the morning unless you like getting dizzy as all the blood sinks to your feet until your heart starts bringing it up again.
Another side-effect is that your brain starts working like it’s on NZT, presumably because ketones are like nitrous oxide to the brain (I have wondered what fasting longer while on Quantum Limitless would be like). So time starts dragging on and days may seem to last forever, sometimes coupled with not feeling like doing anything yet also being bored out of your skull. Add to that you’ll start requiring less sleep and it can be a bit taxing.
Once again, these things should only start happening once you’re past the 14 days and your body finds a groove that works. Many people get some kind of spiritual awakening around day 21. I never have, not entirely unsurprising.