After reading for a few days about it, and collecting some facts, I decided to overcome my cultural fear and fast for 3 full days and nights. Only water, avoiding exercise and seeing how it feels.

Your body has an extraordinary array of alternative pathways to get it´s energy. This is a evolutionary advantage to survive starvation longer, while keeping cognitive function and mobility. The main mechanism is glucose (25% of it for your brain, which gets preference always). Glucose from sugars, carbohydrates, or stored as glycogen in your liver and muscles. After ~10h of no eating (or 2 running) you deplete your reserves. Then the body breaks down fat reserves into glycerol that is then converted into glucose. The liver also ramps us conversion of fatty acids for energy, which produces keton bodies that can be used by all organs, including the brain. (One of the byproducts is acetone which is released by breath and urine.) After a several days, the cells start to break down muscle tissue to get the aminoacids that can be converted into glucose. I do not know, however, what happens with the rest, like vitamins, electrolytes, minerals, … or the vital bacteria on our intestines.

Fasting also changes the mind. Some of the coping and metabolic mechanisms trigger mood changing drugs like gluco-corticoids, epinephrine, catecholamine … Fasting can also help migraines, epilepsia, anxiety, depression… This is both accounted in historical texts, research and the fact that many cultures and religions include fasting as a holy practice.

(Limited) research as also shows [e.g.] that on rats and humans, fasting, and intermittent fasting in particular, is correlated with less oxidative damage and inflammation, optimized energy metabolism, lenghtening lifespan, protection against diabetes, cancers, heart disease, neurodegeneration, reduce obesity, hypertension, asthma, and rheumatoid arthritis.

I don´t know where the healthy point is, but is probably closer to calorie reduction or intermittent fasting, than it is to eggs and bacon for breakfast and Chipotle for lunch.

In my experience, at first it felt normal, just a bit hungry after I missed my breakfast and lunch. Just water whenever I felt like drinking. Then I, stopped feeling hungry, and I felt a little bit dizzy, weak, so I avoided exercise. But fine mentally and in good mood. After 2 days I sometimes felt “emtpy” on the stomach, or a tingling sensation in the muscles, heart beating a little faster for a while, but nothing worrying. I went for a 2 hours walk and chat with a friend. Not sure if true, but I felt my senses more acute, my sense of smell and hearing in particular. The people I talked to didn´t notice anything if I didn´t tell them.

I feel I could have lasted more than 3 days, I didn´t have urge to eat (which doesn´t make evolutionary sense), but for a first experience seems enough exploration in unknown territories. Some people told me they fasted for 7 days. It´s good to get to know your body and where you can safely take it, but 3 days seems enough for a while.

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