What happens when we stop eating? The human body isn’t like a car – it doesn’t just chug to a halt when you stop putting fuel into it. Rather, the human body has developed all sorts of survival strategies for when we stop giving it food.
To keep itself going, the body will begin to cash in any energy supplies it has previously stored up. There are a few different ways the body stores energy, but the most important for long-term survival is fat.
In the complete absence of food, the body will survive for as long as it can by breaking down body fat to get the energy it needs to function. Muscle will also be broken down but fat will be the main fuel source. The more body fat you have, the longer you can survive, so an obese person will normally last much longer than a skinny person. So while you may wish for a skinny body right now, if there were a famine then you’d be thankful for every pound of fat you had.
Once all of the fat back-up energy is used up then we’re really in trouble. At this point, the body is going to start breaking down the only thing it’s got left – its own internal organs like the liver and the heart. Death as a result of organ failure will happen in a normal-sized person after 40-60 days of starvation.
But just how long could a person last without food? In 1965, an obese Scottish man weighing in at a whopping 207kg (32st 8lb) arrived at the Department of Medicine at the Royal Infirmary in Dundee. He was sick of being so large and wanted to burn through some body fat – fast. The medical staff provided him with necessary fluids and monitored his progress. He lasted an incredible 382 days – over a year – without eating, and ended up at 82 kg (12st 13lb). We don’t know what his first meal was after the fast, but I bet it tasted delicious.
Despite this Scotsman’s success story, fasting is very rarely a sensible idea and can lead to all sorts of very serious health problems. For some advice about losing weight in a healthy way, click here.
J. Runcie, T. E. Hilditch, (1974) Energy Provision, Tissue Utilization, and Weight Loss in Prolonged Starvation, British Medical Journal, 2, 352-356 DOI: 10.1136/bmj.2.5915.352
W. K Stewart, L. W. Fleming, (1973) Features of a successful therapeutic fast of 382 days’ duration, Postgrad Med J., 49(569): 203–209 PMCID: PMC2495396
Answer by Nick Waszkowycz