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A recent question discussed how to maximize water retention on a desert hike. One answer suggested that 100g of protein lead to 800ml loss through urination, so protein intake has to be minimized.

What are low protein hiking friendly foods that minimize water loss?

Special non-thirst provoking foods have been developed for lifeboats, these look like ordinary cookies:

Ingredients: Sugar, Enriched Wheat Flour, Partially Hydrogenated Vegetable Shortening (Soybean & Cottonseed Oils), Corn Starch, Wheat Gluten, Dextrose, Desiccated Coconut Preserved with Sodium Metabisulfite, Corn Syrup, Contains less than 2% of the following: Soy Lecithin, Guar Gum, Calcium Propionate Preservative, Citric Acid, Salt, Ascorbic Acid, Ascorbyl Palmitate, Niacin, Vitamin A, Palmitate, Riboflavin, Thiamine Mononitrate.

Here is a datasheet for a similar product, the bar contains:

18g fat, 36g carbs, 5g protein Wheat flour, vegetable fat (palm), sugar vitamins C, B1, B6

Protein:carbs is about the ratio found in wheat flour with some extra sugar. Nothing extraordinary.

Not very appetizing and also for sedentiary people sitting in a lifeboat.

That brings up the question: What are more realistic food options?

What about salt? Salt increases water retention and is needed to replenish losses through sweating. What is the best way to take in salt? A salty meal (e.g. fatty fried bannock) + water, or a survival cookie + electrolyte drink (oral rehydration solution / gatorate).

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    Fat also takes water to digest, while stored glycogen releases water when used. I haven't seen hard evidence that this water is usable, but I think it should be, especially if the effort and training are such that fat is being burnt from the start (one of the goals of fasted training). This only matters for one day, but carb loading with plenty of water wouldn't be be a bad idea before the first day or a one day trip. – Chris H Nov 2 at 9:19
  • Interesting question. Do you think the effect is relevant given that you are in a 'normal', i.e. non-emergency, situation with more or less regular water supply? Data on a carbohydrate-rich diet would be interesting for a comparison. – Alexander Nov 2 at 12:17
  • Given the numbers cited below, I don't think that the food will affect your water use enough to matter. In hot desert conditions your choice of clothing, and timing of your activity will be far more important. – Sherwood Botsford Nov 6 at 16:59
  • Liveboat rations are meant to sustain life. They are deliberately unappetising so that they are still there in the lifeboat. (Imagine a lifeboat with fine chocolate as the emergency food...) The next criteria is that they store for years without spoiling. The final criteria is that they be cheap. Most are thrown away unused after they expire. – Sherwood Botsford Nov 6 at 17:01
  • Reminds me of the military chocolate designed to taste “a little better than a boiled potato”. interesly.com/military-chocolate-bar-boiled-potato – pacaxa Nov 7 at 1:14
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I believe, the concern about foods that do not provoke thirst is relevant only in situations where you need to use water sparingly, such as in "survival" situations.

The effect of macronutrients on water balance

In another answer I said that protein stimulates urine production and thus water loss (100 g protein > 800 mL urine). During the metabolism of 100 grams of protein, 42 grams of metabolic water is produced, but in summary (800 - 42 = 758), this is still 758 grams of net water loss.

The metabolism of carbohydrates and fats does not result in wastes that would need to be excreted through the urine, so they do not cause any water loss through urine. Also, 100 grams of fat produces 110 grams of metabolic water and 100 grams of carbohydrates 60 grams of water, so they both provide net water gain. Anyway, these are small amounts and I personally wouldn't eat 100 grams of additional fat just to get 110 grams of additional water.

Examples of low-protein foods (per 100 g):

In general, nutritious foods relatively low in protein are cereal and potato products, chocolate and dried fruits.

The effect of salt on water balance

The association between salt intake and water balance in the body is quite complex, but according to Karger:

...the urine volume (and thus the fluid intake) remains unchanged over a large range of sodium intakes.

According to the study Sweat rate and sodium loss during work in the heat (Journal of Occupational Medicine and Toxicology, 2008, the sodium needs increase during physical work in a hot environment:

Sweat rates were higher and sodium concentrations were lower in the summer (acclimatised) than the winter (unacclimatised) trials. Sweat sodium concentration was reduced on the second day in summer but not winter.

People working in moderately hot conditions for 10 hrs on average will lose between 4.8 and 6 g of sodium (Na) equivalent to 12–15 g of salt (NaCl) depending on acclimatisation. However due to the substantial interindividual variation in sweat rate and sodium concentration individual losses may be much higher.

Oral rehydration solution in powdered form could be appropriate for someone who loses a lot of sodium with sweat. One packet of the powder for the standard WHO-ORS solution contains about 2 grams of sodium. In context of desert hiking, sports drinks and regular foods are relatively low in sodium.

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    Great answer; well researched. I would add one thing: Keeping the scientific factors above in mind, hiking is supposed to be enjoyable. Having adequate energy provided by the fuel you ingest is part of the equation. Having what you eat be tasty and nutritious is vital. I pre-make many of my meals used on backpacking trips. I dehydrate and vacuum-pack. I find little difference in what I eat in different outdoor environments, with the exception of hot food. In cold temps, it is essential. In hot environs, I eat hot food much less often. – M.Mat Nov 4 at 21:04
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    Very interesting, especially the fact that Na intake does not affect water retention in equilibrium. – pacaxa Nov 5 at 3:09

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