How long could one survive eating yourself?

11 November 2012

Question

I suppose the question could be posed relative to any higher animal .

My unvarnished question and maybe more palatable as "thought experiment"

I recall in past that humans can last about one month with no food. If one sets aside medical complications , how long could a person live if somehow he had to live on amputations of his own body. I assume that piecemeal would too much of a shock . What if , for example , he fed on legs and arms?

Sorry for this one but made for interesting discussion as to equilibrium of energy Rob Faraone

Answer

We put this to Louise Anthony, a medical student at Addenbrookes hospital, Cambridge...

Louise - To work out how long someone could survive by eating their own limbs, we need to make a number of assumptions.

Firstly, we assume that the surgery and subsequent possible infection itself didn't kill them, and we'll ignore the massive energy demands of healing from such an injury. Then we need to assume that you can store your freshly harvested limbs safely, and that you have some cunning way of feeding yourself once you've removed both your arms.

So, with that in mind, we need to know what our daily calorific demands are, and how much energy is available in our limbs.

Firstly, how much raw limb is there to harvest? According to figures collected by NASA for their average 82.5Kg crew member, the arms and legs make up approximately 40% of body mass - in this case, around 32Kg.

To work out how much energy is available from this, we need to use something as a proxy, because little is known about the calorific value of human meat. In this case, we'll use uncooked pork chops, which, according to a well known high-street supermarket, offer 213 calories per 100g. This means that our 32Kg of limbs could provide an impressive 68,000 calories.

But how long would this last?

The World Health Organisation has an equation that we can use to calculate daily energy requirements. For a male in his 30s, this is 11.6 x weight in kilograms +879. To take into account level of physical activity, this is then multiplied by an "activity factor" of 1.2 for sedentary people up to 1.4 for people with very active lifestyles.

Again, we need to make some big assumptions here, as a person with no limbs will have a very different balance of lean muscle vs other tissue, which will alter their metabolic rate.

Using this equation for the remaining 50Kg man, we get a daily requirement of approx 1750 calories per day.

At this rate, our 68,000 calories of human limb should keep our survivor going for around about 39 days, or hopefully long enough to be rescued.

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