What's the longest you've fasted...

Bad Panda wrote: »

14 days is pretty impressive.

Summary
A 27-year-old male patient fasted under supervision
for 382 days and has subsequently maintained his
normal weight. Blood glucose concentrations around
30 mg/100 ml were recorded consistently during the
last 8 months, although the patient was ambulant and
attending as an out-patient. Responses to glucose and
tolbutamide tolerance tests remained normal. The
hyperglycaemic response to glucagon was reduced and
latterly absent, but promptly returned to normal during
carbohydrate refeeding. After an initial decrease was
corrected, plasma potassium levels remained normal
without supplementation. A temporary period of
hypercalcaemia occurred towards the end of the fast.
Decreased plasma magnesium concentrations were a
consistent feature from the first month onwards. After
100 days of fasting there was a marked and persistent
increase in the excretion of urinary cations and
inorganic phosphate, which until then had been minimal.
These increases may be due to dissolution of excessive
soft tissue and skeletal mass. Prolonged fasting in this
patient had no ill-effects.

There have been reports of five fatalities coinciding
with the treatment of obesity by total starvation
(Cubberley, Polster & Schulman, 1965; Spencer,
1968; Garnett et al., 1969; Runcie & Thomson,
1970). One was attributed to lactic acidosis during
the refeeding period following a 3 week fast (Cubberley et al., 1965). Two were considered to be due to
ventricular failure, occurring during the fast, at 3 and
8 weeks respectively in patients who had shown
evidence of heart failure before beginning the fast
(Spencer, 1968). One patient (Runcie & Thomson,
1970) died on the thirteenth day of his fast from small
bowel obstruction. Only one of the five 'fasting'
deaths has been associated with a fast of more than
200 days' duration. It occurred during the refeeding
period after a fast of 210 days in an apparently well
young woman (Garnett et al., 1969).

Most people on a 'western diet' have years of gunk stuck to the walls of their intestines (meant to lead to cancers/illnesses etc). Good to give you intestines a break and clean them out every once in a while. Gross but very healthy.

rocky wrote: »

The brain needs glucose. Glucose is stored as glycogen in muscles and liver. An uneducated guess, but I'd say you definitely ran out of it in your fast. After your liver glycogen reaches a low level, the body then turns to muscle for generating glucose from protein/amino acids.

Mellor wrote: »

When the body is using fat as a main energy source it produces ketones as a by-product. These can replace glucose as the brains fuel.
I don't think they can ever replace 100% of energy requirements, but if they are providing 90% or so it reduces the amount of muscle the body consumes via glucogenesis (spelling?).

I've no idea how long glycogen stores would last if you are sedantry while fasting. But probably a while, it takes most of a marathon to deplete them.

After the diet has been changed to lower blood glucose for 3 days, the brain gets 25% of its energy from ketone bodies.[4] After about 40 days, this goes up to 70% (during the initial stages the brain does not burn ketones, since they are an important substrate for lipid synthesis in the brain).