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Is it actually useful to ration food?

What is the difference between eating a little bit of food at an interval and eating enough to be full at once?

I'm getting the same amount of calories/nutrition** regardless of when I consume it, so who cares? Why not just eat whenever you're hungry to the point of satiety?

Is that an overly-simplistic view?

** I suppose there could be a difference in the percentage of nutrients absorbed. If I get too much of a nutrient, perhaps my body will excrete it, so, in that case, it's better to consume it periodically when your body needs it.

The scenario is being stranded somewhere not knowing when rescue will come - so generally no activity.

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    If I get time to find suitable sources I'll write this up into an answer. Consider endurance exercise: your body uses its fat reserves but the rate at which this can be done is fairly limited, and it doesn't kick in immediately. Fat burning also works better if you have some carbs in your system even if not enough to fuel you. So starting to burn fat sooner, by rationing, can improve your ability to use your on-board reserves. Further, saving some food for a big effort may be worthwhile (e.g. if you've got to hike out over a mountain pass) – Chris H Apr 17 '18 at 8:19
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    Being discussed on meta – pushkin Apr 18 '18 at 15:02
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    @ChrisH Right, as an analogy: "I have box of matches and some wood. The sum of the energy (matches + wood) is the same no matter what order I burn things so I'll burn all the matches first" – JimmyJames Apr 18 '18 at 20:47
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There are several reasons why I think rationing is useful.

  • Morale - If you eat all your food on the first day you won't have anything to look forward to. If you eat a little bit twice a day you can look forward to your next morsel instead of regretting eating all your food. Meals become a break in the monotony and something pleasant you know will be coming. Being able to focus on your next "treat" might be the thing that keeps you from total despair. Also if nothing else it gives you something to do for a few minutes every day...

  • Forcing Efficiency - Sure you will put the same amount of calories into your mouth regardless, but your body may not extract the same amount of calories. Unlike water the human body has long term storage capabilities for food/energy. By reducing your calorie intake you force the body to burn those energy reserves, and maximize utilization of the calories you consume. Furthermore this signals to the body that it should hoard its food reserves and seek to maximize the calories it extracts from food.

  • Comfort - You can become accustomed to living moderately to mildly calorie deficient. The hunger is always there but it is easy to push it to the background. When you literally don't have anything to feed your body this is much harder. That's why people who truly don't have any food resort to desperate measures like eating dirt cookies.

  • Thrive vs Survive - The amount of calories you need to survive is less than the calories you need to thrive. Sure there are generic calorie intake recommendations. This is the recommendation for people to thrive. To meet basic survival needs you need less calories than what you'd need to thrive in the same circumstances.

  • Not Everything Is Stored - Read (and up-vote) the two other answers that mention water soluble nutrients and proteins. There are some vital substances that your body has no effective way to store. You need to keep consuming them, even in small quantities, to survive since that is the only way to keep them in your body.

  • Accountability - People are great at rationalizing things. If you ration your food you won't end up sliding down that slippery slope where you eat "just one more wafer thin mint" until you run out of food. By having an explicit plan in place you know that you can eat X food per day. Think of this like credit cards. No one forces you to overspend but the temptation is there and clearly a significant number of people succumb to that temptation. Now imagine you're sitting in a cave, hungry with nothing to occupy your time. What are the chances hunger and boredom are going to cause you to rationalize a reason to eat just a little bit more if there is no accountability. The accountability aspect is even more crucial when you're part of a group. This is why setting explicit rations is better than soft metrics like "eat when hungry but not too much."


I don't have any official sources to back this up, but I have some experience rationing food. My cousin and I spent several months cycling around Europe with little money and consequently not much food. By the end of the trip I had lost significant weight, but overall the trip was quite enjoyable. It is interesting though when I reflect on my memories food has an unusually strong imprint. Meals that would have been unmemorable normally are seared in my memory. I'm sure that is due to the constant and inescapable hunger. I think if we hadn't rationed, the trip either would have been much shorter, or more driven by hunger during our fasts.

  • I'd think that the "forcing efficiency" is at least also (if not predominantly) due to limiting energy output when nutritional input does not meet demand. Reactions like getting cold easily/unusually when hungry, or physical work demanding unusually high amounts of will power. – cbeleites Apr 17 '18 at 12:00
  • I don't understand your point on "Forcing Efficiency". You say that you're not going to extract the same amount of calories, which I agree with, but then you go on to say that your body has long term storage capabilities for food. Doesn't that basically contradict the previous point? I say "basically" because I guess technically you're not extracting the calories, but you are still storing them and using them down the road when you're low on energy. – pushkin Apr 17 '18 at 13:56
  • @pushkin The long term storage refers to the fat already on the person. The forcing efficiency refers to the fact that the less you eat, the greater the proportion of that food your body can actually extract. – Shufflepants Apr 17 '18 at 14:00
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    @pushkin It's more that your body can only extract and store so much. Some of what you eat just goes straight through you without being absorbed and goes to waste (as it were). And the proportion of waste to what you actually absorb and use goes up the more you eat. And then in a addition to the limits on what you can absorb into your blood, there's a limit to how much of that can be converted to fat should you not need all of that at the time. Further, fat/energy is about the only thing you can stock pile. You can't stockpile many vitamins/proteins. – Shufflepants Apr 17 '18 at 14:29
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    I got to be the one to cast the 100th vote :) – Charlie Brumbaugh Jun 12 '18 at 2:16
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Aside from the previously mentioned micronutrients, your body doesn’t really store protein in any significant way, so in order to ‘repair’ your body you need a relatively constant stream of protein (or rather, amino-acids). Nothing bad happens if you fast for a short while, but it does mean you will obtain amino acids from breaking down your own muscle which will cause issues in the long run. If you would eat all your food at once, you would likely not even use all of the protein for repair but rather convert it to energy (fat). And that is if you could even digest all of it.

Additionally, you can also not store essential fatty acids other than in your stomach after eating. Again, nothing bad happens immediately if you run out but over longer periods it can affect many things such as hormone levels.

The other thing is that your body can only effectively use its own fat reserves if it has some food to initiate the process (that’s the dumbed down version, you can read more on https://en.m.wikipedia.org/wiki/Citric_acid_cycle?wprov=sfti1) If you don’t have food then using your own fat reserves also means breaking down your muscles to initiate the process.

All good reasons to ration food.

  • But isn’t the reduction of muscle mass actually a good thing in a starvation scenario? Muscles consume energy even when not used. Unless you know that you’ll have much better access to food after a certain amount of time and want to minimize muscle loss until then. – Michael Apr 17 '18 at 14:53
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    @Michael fair point but I am not sure how rationally your body will break this down. I'm no expert on this either but whether it starts breaking down from the heart muscle or your abs, I'm not sure. Also I think in many situations you would prefer not to be 'sore' which will probably happen if you use your muscles a lot such as for walking but instead of being able to repair them with protein from food, you actually break them down more. Maybe if you were a bodybuilder it makes sense to first lose some of those muscles though. – Sebastiaan van den Broek Apr 17 '18 at 14:59
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There are many nutrients that your body cannot store, or not in decent extra amounts. Water, salt, potassium, vitamin C, etc. You will rapidly excrete these, and then greatly feel the lack of them when you are fasting for days.

Yes, you can to some extent gorge yourself on macronutrients (fat, carbs, protein) because these will be stored as body fat fairly efficiently. However, if you are planning to be functional during your famine, it is no good being overfed for a couple of days then weak with hunger for several more. You can reduce your energy consumption quite considerably from ad libitum levels without feeling unwell. Why do we feel weak when we still have fat stores to draw on? Because it takes time to get into ketosis to fully access those stores, and the process wastes some energy, and in times of famine we have evolved to feel tired so as not to waste energy dancing or whatever.

  • "There are many nutrients that your body cannot store, or not in decent extra amounts. Water, salt, potassium, vitamin C, etc. You will rapidly excrete these, and then greatly feel the lack of them when you are fasting for days." Admittedly I'm not too familiar with these processes, but will your body not excrete them if it has no need for them (e.g. you drank too much water). What if you're careful to drink only when you're thirsty and then stop without going over. – pushkin Apr 17 '18 at 14:24
  • @pushkin In case of water you still will lose it by urinating, sweating and breathing. If you limit your water intake, then your kidneys switch to a kind of "economic mode" (which may not be healthy, but necessary to survive). I am not sure how it affects breathing and sweating though. – abukaj Apr 19 '18 at 15:01
  • What's the calorie/protein loss from converting sugars and proteins to fat, and later produce them again from fat? For example, gaining weight may involve creating new fat cells. I imagine it's substantial. Avoiding that detour must be beneficial. – Peter A. Schneider Apr 19 '18 at 15:35
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    @AmyDeeDempster Newer research appears to indicate that new fat cells are being formed, and quickly, too: "The increase of fat cells in obesity is particularly problematic because once established the cells are difficult to eliminate." – Peter A. Schneider Apr 20 '18 at 10:19
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    @PeterA.Schneider it is impossible to create protein out of fat. – Sebastiaan van den Broek Apr 21 '18 at 6:45
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The simple answer is that yes it does make sense to ration, see the stories of the men who survived the Essex or the Mutiny on the Bounty or the Chilean Miners or many countries during wartime.

From a mathematic point of view, one rations when does not have enough food for the timeframe between now and a resupply. If you eat enough to be full all the time, you will run out of food.

When one is backpacking, one wants to make sure that there will be enough food to finish the trip and while that may not mean eating less than needed, you do want to keep an eye on how much is left to make sure you don't run out.

From my experience backpacking with fewer calories than needed, there are some tricks to make it easier.

  • It's easier to sleep on an empty belly than to hike on one.
  • Eating your food reduces the weight you carry and will speed you up so don't stop eating.
  • It can make sense to speed up the pace, you are going to burn calories regardless of what you do, and getting back to the trailhead in less time reduces the number of calories required.

The short answer here is that if it didn't work, I don't think it would have been used to such an extent historically.

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    "If you eat enough to be full all the time, you will run out of food." True, but you would also have consumed just as much food/nutrition as if you had waited. That's exactly the motivation behind my question - is there an actual practical advantage to holding off on eating whenever you're hungry. – pushkin Apr 17 '18 at 13:43
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    "The short answer here is that if it didn't work, I don't think it would have been used to such an extent historically." While one could buy that argument on the surface, one could also say that maybe they just didn't know any better. I was really looking for scientific arguments proving or disproving what I said in my question. – pushkin Apr 17 '18 at 13:46
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What I've always understood to be the rationale, and doesn't seem to be directly addressed with the other answers, is that the human body adjusts its metabolism to its resources. If you gorge on all your food, you're signalling to your body that there's plenty of food. If you eat only a little bit a day, you signal to your body that it should go into starvation mode. This means not only burning fat reserves as noted in other answers, but also reducing metabolism (note that this means that keeping warm is an important part of survival). This is especially useful in cases like the Chilean miners; there was very little activity they could do to help their rescue. Survival came down simply to staying alive long enough for others to get to them. In a case like that, signalling to your body that minimizing calorie use should be prioritized way above remaining strong and active is going to help your survival chances. On the other hand, if you're in a situation where strenuous physical activity is needed to survive, but you don't have much food, you're in a double bind.

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    This is the concept I was going for with my "forcing efficiency" bullet. You said it better than me so you have my up-vote. – Erik Apr 17 '18 at 15:46
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    That's what everyone trying to lose weight has to fight. You eat less, your body uses fewer calories. Of course when you have no food and want to survive, it works in your favour. – gnasher729 Apr 17 '18 at 21:32
  • If you're in a situation that calls for strenuous physical activity you should probably be killing and eating something else. – Wayne Werner Apr 17 '18 at 22:26
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One aspect not discussed much in other responses is that the body actually has a fairly limited capability to process food at all.

Your gut is a conveyor belt that never stops, not a production line where it does each step properly before allowing it to move on. If too much comes through, you can't process all of it before it passes out of you again.

If I eat all the food I need for a week in one sitting, most of it will pass through me only partially digested and critically, won't be edible afterwards, effectively wasting the vast majority of its value. (I'll also probably throw up, but that's pretty much the same result)

An extreme example of course. But to a degree, eating smaller volumes of food at intervals will digest more efficiently simply because your stomach acids and digestive tract have less to deal with and can devote more 'attention' to it.

When you need to stretch your efficiency, you waste food if you eat more than you can properly digest at a time, so consuming less in each sitting will allow you to make better use of each meal and so stretch your reserves for longer.

  • The question is about eating (almost) normally vs. rationing (i.e. clearly less than needed), so in all scenarios far away from overeating. Can you link literature that shows a decrease in nutrient uptake between those two scenarios? – cbeleites Apr 23 '18 at 7:17
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I think the simplest answer is also the best in this case. This should work for (what I presume is) the majority of rationing cases.

Q: Why are you rationing?

A: Because you do not have enough food and need to survive until you get more. Once you run out of food you will have no option to ration, as then your only choice is to fast.

I think that the "do not have enough food" part is key here to make sure we are on the same page. If you have enough food but are not eating it, then you're dieting, not rationing. Maybe this is not correct given the technical definitions of the words, but I think this fits with most peoples' view of what it means to ration: to limit the use to avoid running out entirely.

If I have 3 days worth of food but I think I might not be able to get any more food for 6 weeks, then the math is simple. I can...

  1. eat normally for 3 days (I'll assume 3 square meals per day), then hope that I can go completely without food for 5 weeks and 4 days more without dying, or

  2. not eat for a few days (assuming I'm initially healthy, otherwise skip this initial fast), then eat half of what you consider a normal meal once every two days, then hope that you can go completely without food for a few days more without dying.

3 days * 2 times less food per meal * 2 days between eating * 3 times fewer meals per day

= 36 days worth of rationed food instead of 3

Would you rather start a 39 day fast while starting in your normal, healthy state of body or a 3 to 6 day fast in a less healthy, starving state of body? You probably will die in the first scenario since you likely cannot survive 5 and a half weeks of zero nutrition. Yet many people all over the world are used to eating several times less food than you or I every day as a normal part of their lives for their entire life.

If you risk death from having zero food, we are told by the experts (I use that term loosely, but I would rather heed the advice than risk death) that you will die within a few weeks of eating nothing. A few weeks. People do not starve to death from a few weeks of severe malnourishment when they eat a tiny amount, rather, they live long, unhealthy lives for months or years.

Summary

You can stay alive for a long time in an unhealthy state of starvation as long as you keep eating small amounts of food, but once you stop eating altogether (which is what will happen when you run out of food from eating it to soon) the timer to a 100% certain death starts counting since people generally survive only a few weeks without eating anything no matter how much they bulked up first.

So the rationing question becomes this...

Choose one: Do you want certain death in a few weeks, or do you want to live a malnourished, unhealthy life for a lot longer and maybe (or maybe not) die in months or years?


Caveat (warning)

If you are do not know how long you will need to ration, you need to make sure you do not over-ration. You can die from starvation even while you are still eating sparingly.

Some people have died from hunger or thirst even when they had more food or water available. They rationed so hard they died before using all their supplies. Please don't die of thirst when you still have water left. How much is the right amount? It's hard to say, and either way is a gamble.

If you are stuck in a dry mine, the middle of Antarctica without a heat source, or in a prison cell after a prison is abandoned, then I am sorry for you. Otherwise, food and water can be procured in the vast majority of locations on Earth, even harsh ones. Ration softly and spend your remaining days as a race to learn to extract food and water from wherever you are.

See also this other outdoors.SE question where the amount of time one can survive with zero food is discussed a bit more.

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