There’s an urban legend that speaks of a man who managed to shed over (113 kilograms) 250 pounds simply by not eating anything for over a year. But is it actually possible for the human body to go without food for this long? Remarkably, this strange story isn’t just a modern-day folk tale, it appears to have actually happened, albeit with one or two minor caveats. 

Published in the Postgraduate Medical Journal in 1973, a case study by doctors at the University of Dundee School of Medicine documents the story of a “grossly obese” 27-year-old man in Scotland undergoing 382 days of fasting in an attempt to lose weight.

Staggeringly, the man appeared to reduce his weight from 206 kilograms to 81 kilograms (456 to 180 pounds) and remained in surprisingly good health. Five years after the extreme fasting, his weight remained stable at 88 kilograms (196 pounds).

“Initially there was no intention of making his fast a protracted one, but since he adapted so well and was eager to reach his 'ideal' weight, his fast was continued into what is presently the longest recorded fast (Guinness Book of Records, 1971),” the doctors wrote. 

He did not eat any solid food during this time, although he was given potassium and sodium supplements, vitamins, and a small amount of yeast (which contains protein). And if you were wondering about pooping, the doctors note that he only had a bowel movement every 37 to 48 days. 

The man regularly visited the hospital to have his blood and urine tested to check his blood glucose levels and plasma electrolyte concentrations. Although most of these levels slipped as the months went on, he managed to remain in surprisingly good health and good spirits.

“Despite the hypoglycemia [low blood sugar] the patient remained symptom-free, felt well and walked about normally,” the case report added.

So, how is this possible? 

If you are eating food regularly throughout the day, your body will obtain most of its energy from glucose in your bloodstream and liver. Cells use this glucose for the synthesis of ATP, a molecule that carries energy within cells. If there's no glucose immediately available in the blood or liver, we are also capable of producing it from glycogen, a long chain of glucose that can be stored in the liver and muscles until it's required and broken back down. Beyond that, the body can break down body fat into glycerol, which can eventually be converted into glucose, and free fatty acids, which can be converted into ketones.

Since the man had such a plentiful store of glycerol, located in his heaps of body fat, he was able to live off this last process for a surprisingly long amount of time, with just a little help along the way from supplements. However, it's extremely likely that he would have died if it wasn't for the potassium, sodium, and yeast supplements, which are essential for biological functions inside the body. For example, potassium is absolutely essential to nerve impulses and muscle contractions, among many other bodily processes.

Nevertheless, if you are overweight and looking to lose some pounds, fasting is not an advisable way to go about it at all. Many people have died attempting to fast and the risks of this extreme "diet" far outweigh the benefits.

[H/T: Snopes]