That is extremely unhealthy diesel. I would advise against repeating that. From my own experience, when ketosis kicks in you gain a certain clarity. That is the most desirable aspect of fasting for me; an induction of death, a triumph of will over biological prerogative. Do not harm yourself to do it though, that's just silly. Make sure you get micronutrients and at least some calories every few days.
great ideas. im already done with the first one. how often and for how long should one fast and deprive themselves though? i don't particularly want to develop any fucked up conditions or die of a heart attack.
I will take your question to be; how long should one fast to receive intellectual/spiritual benefit? An example that comes to mind is the Prophet Muhammad, whatever your views about what he fostered, the man was a thinker, at times an ascetic, and a great faster. In the spiritual traditions of the Sufis of India (also Islamic), there are accounts of people who would fast on alternate days, or for 3 months out of a year etc., obviously influenced by the example of Muhammad. The method of fasting is quite specific: Rise before sunrise, have some optional intake (water, a very, very light meal), then till sunset deprive yourself of all food, drink, sexual congress, drugs (including tobacco) and poor behaviour (hatred, spite, jealousy, envy, backbiting, whatever you consider to be unworthy in this vein). Meditate often. At sunset break the fast with another light meal/water. From experiencing it, it is effective, but you may tailor it to your requirements and preferences. It could be a useful example. Performing it with ritualistic deliberateness, with stated and felt intent, is also powerful and symbolic; adding to the benefit in my humble opinion.
From the perspective of your health, do not completely deprive yourself of calories for longer than 3-4 days. During the first few days of starvation, the body uses up its stores of glucose. After the 2nd/3rd day, breakdown of fatty tissue begins. If starvation continues however, over the course of just over a week the body begins to also use up its own protein. You certainly do not want your body metabolizing desirable protein (muscle) to generate energy. Let it subsist on fatty acids/ketone bodies. Fatty acids are breakdown products of stored fat which are metabolized for energy by almost all tissues of the body. However, the brain can only use either pure glucose or ketone bodies as a source of energy, its cells do not have the chemical mechanisms to use fatty acids. Ketone bodies are a byproduct of metabolism of fatty acids in the liver, they are three chemical compounds that can be thought of as slightly altered building blocks of fat. At about day 4 of starvation, ketone bodies account for ~70% of the energy that the brain receives. As I mentioned earlier, in my experience this produces a clarity of thought that is worth seeking.
The lines directed at diesel also apply. Cultivate thirst, but do not dehydrate yourself unnecessarily; get a good amount of water in you over the course of the day. Ketosis makes the blood acidic (reduces pH), and dehydration can exacerbate this effect. It is unlikely to be harmful unless you overdo it, but it does require the regulatory system in your kidneys that handles blood pH to work quite a bit.
Some traditions relating to fasting by the Prophet Muhammad:
-Narrated Muslim al-Qurashi: "I asked or someone asked the Prophet (peace_be_upon_him) about perpetual fasting. He replied: You have a duty to your family. Fast during Ramadan and the following month, and every Wednesday and Thursday. You will then have observed a perpetual fast.
(Translation of Sahih Muslim, Book 13, Number 2426)"
-Narrated 'Abdullah bin 'Amr bin Al-'As: "Once Allah's Apostle came to me," and then he narrated the whole narration, i.e. your guest has a right on you, and your wife has a right on you. I then asked about the fasting of David. The Prophet replied, "Half of the year," (i.e. he used to fast on every alternate day).
(Translation of Sahih Bukhari, Volume 3, Book 31, Number 195)"