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So say that a 5'6/6 feet person is shrunk down to action figure size(around 6 inches tall/12x smaller) or comes from a human/humanoid species that is naturally that size, how much food and drink would they need in ounces and fluid ounces to get by normally and not be eating the bear minimum or eating enough for 2-3 people assuming that they need equivalently as much as a normal-sized person?

What about people that grew to 66-72 feet tall(Gulliver's Travels giants size) or are naturally that big? How many pounds(or tons maybe) and gallons of food and drink respectfully would they need in the average day again assuming they have equivalent food needs of normal-sized humans but scaled up and that they are not trying to 'stretch' food or or 'pigging' out on it.

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  • $\begingroup$ If by the phrase "equivalently as much as a normal-sized person" the question means the same amount of food per kg of body weight, then it is a trivial primary school arithmetic problem. If this is not the intended meaning, then the question needs more details or clarity. (And the premiss is unbelievable, because heat loss is proportional to surface area. Small animals need much more food per kg of body weight than big animals, because the vastly different surface to volume ratio means that small animals consume of lot energy to stay warm.) $\endgroup$
    – AlexP
    Jan 28, 2023 at 14:27
  • $\begingroup$ I mean like how would it scale up or down for a human, negative effects of the square-cube law be danged. I am not the greatest at math, that is why I asked. @AlexP $\endgroup$ Jan 28, 2023 at 14:37

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300 calories and 30 million calories.

Homework Do a more detailed search and check are the figures for calories or KiloCalories. Human food labels are called calories but are actually KiloCalories (Kcal).

The little human is $\frac{1}{12}$ the height of the normal $6$ ft human. So they are $\frac{1}{12}^3$ the weight. Shrinking a $70$ kg person we get $\frac{70}{12^3} = \frac{70}{1728} = 0.04051$ kg or about 40 grams. Googling around says a mouse weights about 20 grams and needs about 150 calories. So the small human needs about 300 calories.

Enlarging a $70$ kg person by twelve increases the mass by $12^3 = 1728$ times. So we get $70*1728 = 120960 $ kg or about 120 tonnes. About the weight of a blue whale. Googling around says the whale needs 20-50 million calories per day.

This assumes the little person is as zippy and active as a mouse and the big person is as slow-moving as a whale. That is to be expected.

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How to scale?

  • Going from approx. 6 feet to approx. 6 inches, while retaining the proportions, would reduce the body mass by $\frac{1}{12^3}$, so arguably the energy use by organs and muscles should scale by the same factor.
  • The body surface is reduced by $\frac{1}{12^2}$, which means that the proportion of surface area to body mass goes up by a factor of $12$. To overcome heat loss, the midget will have to burn more energy in proportion to body mass, the heart will have to beat faster, etc.
  • The miniaturized digestive system will not be able to handle $12$ times the energy intake without a major redesign, which might lower efficiency.

The giant would have the reverse effect regarding heat loss, but also problems when it comes to bone strength and the stability of the skeleton and muscles. The weight rises with the cube of the size change, the bone cross-section only with the square. This is called the square-cube law.

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  • $\begingroup$ Well, let us assume that the negative effects of the square-cube law are not in effect. $\endgroup$ Jan 28, 2023 at 14:39
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    $\begingroup$ According to open.oregonstate.education/aandp/chapter/… , around 10% of our energy expenditure is spent on heat regulation. So, if 10% of the budget is multiplied by 12, that's basically close enough to adding in an extra factor of one, i.e., doubling the energy consumption relatively speaking. I think the body's ability to thermoregulate will be the limiting factor instead of energy consumption. $\endgroup$
    – Zwuwdz
    Jan 28, 2023 at 17:29
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700 kilocalories for the small guys

50'000 to 60'000 kilocalories for the big guys

Usig the Katch-MCArdle formula it comes out to be around 500-700 kilocalories per day for very active humans that are around the weight of 0.8kg to 1kg at the height you specified, could probably be to the lower ends of 500 kilocalories for very sedentary small people.

700kilocalories seem a lot for someone this small and short, but smaller animals eat more because they lose a lot of heat and maintaing temperature costs a lot of energy.

While your giants will weight something around 5,248.7 lbs or 2380kg(those are skinny giants, because humans struggle not collapsing on their own weight after surpassing certain height to weight ratios), will need around 50 to 60k kilocalories per day, which doesn't seem like a lot.... normal human bodybuilders, strongmen and athletes eat this ammount of food in 6-8 days.

but remember that bigger people lose less heat, therefore they waste less energy maintaing their body temperature.

So in proportion the giant guys aren't gonna be big eaters.

For more bulky and muscular giants, give them a diet of around 110 to 128k kilocalories per day, but keep in mind that in any realistic gravity they would collapse onto themselves and be crushed by gravity, the human spine is not made to handle this size.

You can make the spinal muscles as big and strong as you want, but the human body is just not made to handle this much weight vertically.

world-level athletes seem to die or collpase when their spine is holding or moving straight perpedicular weights around 6 to 7 times their size.

if a 120kg athlete faints while holding 720kg in their hands for a few seconds, don't expect your giant's spine to be able to hold any remarkable weight, also given the fact that bigger animals have a less size to strength ratio. So go and make your giants skinny like oversized giraffes.

if you make your giants be more like gorillas and less like humans, then you could maybe make them heavier than two tons.

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  • $\begingroup$ As a first order approximation, the 15 cm tall person is not more than half a house cat. A house cat needs about 250 to 300 kcal per day. $\endgroup$
    – AlexP
    Jan 28, 2023 at 14:40
  • $\begingroup$ @AlexP I tried other formulas for calculating calories, but I was getting stuff like 40 to 60 kilocalories per day, which seemed too small $\endgroup$
    – calculator
    Jan 28, 2023 at 14:45
  • $\begingroup$ For the biggg animals we don't have direct examples, but for small animals we already have direct comparisons available with existing creatures. $\endgroup$
    – AlexP
    Jan 28, 2023 at 15:02
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If the amount of food required to feed a 6 inch person were proportional to that of a normal sized human, it would take an absurdly small amount to feed them. The daily calorie intake for an adult human is generally 2,000 calories, so the 6 inch person would only require 33 calories (2,000 ÷ 60 inches). This amount of food would be negligible, as it would require only a few bites of a standard meal.

On the other hand, if the amount of food needed to feed a 72 foot person were proportional to that of a normal sized human, it would take an enormous amount of food to feed them. The daily calorie intake for an adult human is still 2,000 calories, so the 72 foot person would require 28,800 calories (2,000 x 72 inches). This is more than enough food to feed an entire family for a week.

In conclusion, if the amount of food needed to feed 6 inch and 72 foot people were proportional to that of a normal sized human, it would take an incredibly small and an incredibly large amount of food, respectively.

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