A while back Demigan had a running series of posts about various aspects biological enhancement for the purpose of designing super-soldiers with an element of (pseudo) science behind them.

You can find his previous questions here:

Creating a scientifically semi-valid super-soldier, part 1: Skeleton

Creating a scientifically semi-valid super-soldier, part 2: nervous system

Creating a scientifically semi-valid super-soldier, part 3: Physical shock resistance

Creating a scientifically semi-valid super-soldier, part 4: respiratory system

Creating a scientifically semi-valid super-soldier, part 5: Heart and circulatory system

Creating a scientifically semi-valid super-soldier, part 6: Radiation protection

Creating a scientifically semi-valid super-soldier, part 7: Hearing

Creating a scientifically semi-valid super-soldier, part 8: Communication

Creating a scientifically semi-valid super-soldier, part 9: Temperature control

One thing I didn't really see mentioned, which I was wondering about, is metabolism. Obviously, a super-solider with powered-up muscles, nervous system, etc. is going to be burning a LOT of energy, even at rest. The post about temperature control is basically asking how to deal with all the excess heat that is created as a result.

Metabolism is the process by which the body converts food/fuel into the energy it needs to function. The higher the energy needs of the organism, the greater the amount of fuel required, or the more efficient the conversion process must be.

In nature, we do see that some creatures have more efficient metabolisms than others. For instance, warm-blooded beasties have more efficiently designed metabolisms than cold-blooded beasties because they need to use additional energy warming their bodies and therefore need to use the energy that they have in a more efficient way.

Increasing metabolic efficiency would also probably help with the temperature problem a bit as well. This article notes:

no energy transfer can be perfectly efficient – that's a basic law of physics. Instead, each time energy changes forms, some amount of it is converted into a non-usable form. In the reactions of an animal's metabolism, much of the energy stored in fuel molecules is released as heat.

Logically, the more efficient we can make this conversion, the less heat will be produced as waste.

Given a super-soldier's high rate of energy usage, how do we stop them from needing to eat constantly, 24/7? The less we have to feed them, and the longer they can survive cut off from supplies, the better. Any ideas for improving these guys' metabolic efficiency or generally finding ways to feed them a more "normal" amount while still powering their high energy needs?

To stay in keeping with Demigan's posts, a good answer needs to be limited to a biological solution, where a body can build, repair and maintain it.

  • $\begingroup$ I retracted my close vote as a duplicate of Demigan's part 9 (temp control), which is a consequence of metabolism. However, I'm Leary of this question because it touches on several of the other questions (like fat retention and temperature control). I'm not completely convinced it's unique enough, especially when such a soldier would need to eat highly concentrated, slow-to-digest foods that have little or nothing to do with the soldier's intrinsic design (food design, yes, soldier design, no). How do the answers to the other questions that touch on metabolism not answer this question? $\endgroup$ – JBH Apr 2 at 6:21
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    $\begingroup$ A car engine can be built, repaired and maintained by a body, but I would hardly call it biological. $\endgroup$ – L.Dutch Apr 2 at 6:29
  • $\begingroup$ How much energy are we talking about, here? Modern society is really good at making energy-dense meals - it's possible that the answer is just "issue them with more MREs so that they can eat multiple MREs at once" and/or "issue them with de-carbonated soda rather than water". $\endgroup$ – nick012000 Apr 2 at 6:33
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    $\begingroup$ Whats wrong with just having them high calorie foods? Considering a Cheeseburger is just 14.2% of your daily intake, your super soldiers could just smash a couple of those down and since their metabolism runs faster, they can eat more that a normal person can. $\endgroup$ – Shadowzee Apr 2 at 6:38
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    $\begingroup$ The temperature control question assumes they're going to be running hot all the time which is thoroughly inefficient. This question opens the possibility of being able to regulate their metabolism to meet the requirements of the situation. It's definitely a different question. $\endgroup$ – Ynneadwraith Apr 2 at 9:58

As high as possible, with the ability to regulate it downwards.

When well supplied and in a combat situation their metabolisms would spike. Soldiers would be able to move and think quicker, and recover from injuries faster. If well supplied while marching this would also give them a mobility advantage compared to other footsloggers over rough terrain (any other terrain and they should be in transports).

When not fighting, they can regulate their metabolism downwards to a more manageable level. Arguably, humans are probably a little too highly metabolised for the large majority of warfare. Sitting in trenches waiting for an attack doesn't require that much energy. They can save on supplies by reducing their metabolism. Platypodes and Echidnas are able to maintain a fairly active lifestyle with body temperatures around 32 degrees celsius. Something like that would allow for a moderately alert fighting force that doesn't require quite so much energy to maintain.

When not on active duty, they could enter a sort of torpor or hibernation to reduce their metabolism as close to zero as possible. For storage during peacetime, or transport at some distance from the front lines this would be ideal. In protracted conflicts, you could always have the majority of your fighting force in torpor with only a select few alert sentries (provided you're confident you can wake your sleeping soldiers in time to respond to an attack). There's also a benefit of having an intermediate torpor state where they are still capable of some activity in case they are cut off from supplies for a protracted amount of time, but still at risk from the enemy.

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    $\begingroup$ Keep in mind that "be able to move and think quicker" would require the body to maintain a slow and fast nervous system that use less energy when not in use. Unfortunately the brain at least takes as much energy to maintain while inactive as when it's active. Otherwise you could perhaps look at certain deep-diving species. To conserve energy they will limit bloodsupply to most organs so only the important things get all the stuff they need. Question then is, how fast can they go to a fully alert status when using such a technique? $\endgroup$ – Demigan Apr 2 at 10:13
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    $\begingroup$ @Demigan Agreed, it would need some significant biological adaptations to get it to work. One option for the brain would be putting areas of it to sleep when it's not required a la dolphins. You're also right that speed of awakening would be critical as well. Even if it takes a long time though, it would be very useful in storage and transit. It's certainly a very effective adaptation for hibernating animals. $\endgroup$ – Ynneadwraith Apr 2 at 11:27
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    $\begingroup$ also keep in mind that metabolic efficiency is a function of temperature (usually with only one peak). pre-heating athletes is a thing. your 'chilling' supers would need an additional organ (brown fat for instance) to heat more rapidly, otherwise they'd not reach full efficiency soon enough in surprise attacks $\endgroup$ – bukwyrm Apr 2 at 14:33
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    $\begingroup$ @bukwyrm Very good point. I expect the speed with which a supersoldier can be roused from torpor would be an area of much research effort. The first bunch to crack a 'fast-awakening' supersoldier would be able to pull a hell of a surprise attack, although it would probably only work the once. After that they'd still have a logistical advantage though. $\endgroup$ – Ynneadwraith Apr 2 at 14:44

Several improvements

  1. The ability to digest what we call dietary fiber, specifically cellulose, and use it for energy. All that is needed here is an enzyme that has the ability to break down cellulose and use it for energy. Making any plant or tree into a source of pure sugar.
  2. Low basal metabolic rate, similar to Ynneadwraith's answer, this is the amount of energy that the soldier's body needs to maintain itself while at rest. There is no reason why this has to be high, as it is only during exertion when this needs to change. The same thing happens in all humans already, so little modification is needed.
  3. Large storage capacity. Normally this is called fat in humans. The super soldier would need to be able to make and burn fat at an accelerated rate in order to charge and discharge their energy reserves (fat).

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