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I posted this question on the Outdoors SE site. There were some good points regarding morale and such, but I'm curious about this question from a purely biological/nutritive perspective.

Copying from other question:

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.

** is the only counter argument I can think of, but then again, if you're hungry, that tells you that your body needs the nutrients, so maybe it's better to just eat now rather than wait.

P.S. before my question on OutdoorsSE was edited, I was also asking about hydration, so comments on that would be nice too, though maybe that warrants a separate question.

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This answer was initially written to describe different effects of few/frequent meals in everyday life. The part about rationing foods in a "being stranded" scenario is at the bottom.

1. Eating vs working time.

Eating until full means you will probably have only few meals per day, so you will be in the "digestion mode" only for some time around the meals. During digestion, the blood flow partially redirects from the muscles toward the intestine (Journal of Surgical Research), so you will have less energy for work around the meals, but more energy between the meals. On the other hand, frequently munching something will constantly keep you in the digestion mode.

2. Blood glucose spikes

Having large meals will likely result in high blood glucose spikes, which may not be optimal, at least not for diabetics (American Diabetes Association).

Individuals with reactive (postprandial) hypoglycemia frequently experience profound fatigue and sleepiness ("crash") after large meals.

3. Nutrients absorption

In a healthy person, the difference in a meal size should not importantly affect the absorption of nutrients. (There may be several interactions between iron, calcium, zinc, phytates, tannins, etc. that can affect the absorption of a particular nutrient, but this is more the question of the meal composition than size).

4. Hydration

If you drink a large amount of water at once (let's say >0.5 L), the water will enter the blood and expand its volume quickly, which will signal the kidneys to excrete some water. This way your drinking will be less efficient and you will need to urinate more frequently. If you drink smaller amounts, water has more time to get from the blood into the cells, before being excreted.

In summary, in the scenario when being stranded somewhere:

Regarding the efficacy of the nutrient absorption and their utilization, I don't see any significant difference between eating small portions or eating until full if the amount of nutrients/calories is the same in both cases. The exception is water, as described above.

Rationing food when stranded could make sense, if you eat smaller amount of food per day (low-calorie diet). Then your body will start to burn its own tissues (mostly fat but also muscles), you will lose weight and consequently your daily calorie needs will decrease. This is just to theoretically answer, when rationing food intake can actually work.

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  • Regarding point 2, I'm not talking about eating big meals per se, I just mean eat when you're hungry rather than keep holding off, because you'll need food later. The first point is fair, but I've edited my question with a scenario, which is stranded somewhere waiting for rescue, so you wouldn't be doing that much work anyway. Having less energy at certain times isn't particularly important to me.
    – pushkin
    Apr 18, 2018 at 14:20
  • Does point 3 apply more to micronutrients, or are you talking about micro and macronutrients? I thought protein doesn't get stored up, so eating high protein meals would lead to me wasting the protein, as it would get excreted.
    – pushkin
    Apr 18, 2018 at 14:21
  • I'm talking about all nutrients (micro and macro). Your body does not directly store proteins after meals, but it can convert and store them as fat, or convert them to glucose. You can imagine if nutrients are not absorbed, they will appear in the stool. A small amount of carbs, proteins, fats and micronutrients will be usually in every stool, but the amount should not increase significantly with large meals.
    – Jan
    Apr 18, 2018 at 14:26
  • Regarding your first comment, energy-wise, you absorb all of your calories with one big meal or several separated ones. For a survival secenario, the main difference between the two eating patterns would be how would you feel, not how efficient they would be. But this is very different with water. You quickly lose all excessive water, because your body doesn't really store it.
    – Jan
    Apr 18, 2018 at 14:44
  • Could you post a summary/conclusion of your points. It sounds like with water, I shouldn't drink a lot at once. point 3 is anti-rationing. point 2 isn't particularly relevant in most cases. I'm not sure what point 1 is suggesting. If I'm stranded somewhere not doing anything, I don't think I would particularly care if I'm in digestion mode or working mode. If I want to be in working mode though, I suppose this is anti rationing. Thanks!
    – pushkin
    Apr 21, 2018 at 17:09

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