I’m wondering about the sodium RDI guidelines and how necessary a certain daily intake of salt is. Some early humans must have been compulsory vegetarians for good stretches of time when they weren’t able to take down some kind of game. If you consumed nothing but unprocessed fruits and vegetables you probably wouldn’t get the current RDI for sodium in a week’s time, so I’ve gotta figure the body has it pretty tightly regulated. I guess my question boils down to: how much sodium does a person actually need to avoid hyponatremia, and would the diet I outlined above (unprocessed plant diet) prevent it?
The RDI guidelines reflect current needs, taking into account modern lifestyles and longevity. Your “early humans” had radically different lives in many respects, not merely the fact that they ate unprocessed fruits and vegetables. Presumably there was enough salt in their diet to enable them to live long enough to reproduce; that’s all that was required.
And for all we know, they may have licked each other’s sweat.
Sea water, animal salt licks and other surface deposits.
The amount of sodium required by the human body is very small, and is affected by the amount of other minerals, like potassium, ingested. Many edible wild plants have a high mineral content, especially in the rootstock. Studies on tropical foragers of the present day have shown they excrete a smaller percentage of the ingested sodium in their urine (and presumably sweat) than the sodium-gulping Western folks, the body making use of what little it gets.
I know it can be confusing, but hyponatremia is not a consequence of sodium deficiency (except very, very rarely). Rather, in essentially all cases, too little sodium leads to ‘volume depletion’, i.e. lack of sufficient fluid in the circulation (arteries, veins, and capillaries) but no change in serum sodium level. (Volume depletion, btw, is similar to, but not quite the same as, low blood pressure.)
Hyponatremia is, 99% of the time, due to excess water and not due to lack of sodium (and, conversely, 99% of the time, hypernatremia is due to too little water).
Phrased differently, serum sodium level reflects the amount of water in the body, and bears no relation to sodium intake or availability (again, except in very rare cases).
If you’re interested, I can flesh all this out in more detail.
We have no evidence of such a thing, and I can’t think of any plausible reason why it would be true.
The only times I can think of when you won’t be able to obtain game will be during extreme droughts and prolonged winters. In both those circumstances the vegetation disappears first, the animals only disappear when they no longer have any food to eat, which will be several weeks after thy have eaten all the available vegetation. As long as you have edible vegetation you will have animals that are surviving on that vegetation.
So while there would certainly have been times when people had nothing at all to eat, and more times when they had nothing but animals to eat, it’s hard to imagine a time when they had nothing but plants to eat.
As large game becomes scarce, humans will certainly switch to foods such as rodents, insects and small birds. There are accounts of San surviving on tubers and the marrow extracted from bones of carcasses, and of Aborigines surviving on tubers and insects, but I can’t recall any accounts of HGs ever being forced to resort to anything like a vegetarian diet.
Is it actually the case, anyway, that a vegetarian diet contains less sodium (proportional to overall nutritional value) than a carnivorus (or omnivorous) one? Plants certainly have sodium in them, and you have to eat a good deal more plant material than animal material in order to get enough protein (and,with most plant-based foods, in order to get enough calories too).
While you don’t need much sodium to maintain life, you do need some, and I have always thought that through most of history, getting enough sodium has been a problem, not only for humans but for all animals. That’s why animals have such intense salt cravings - why for instance I love potato chips, why cattle will walk miles to a salt lick, and why in alpine areas they tell you to piss on rocks instead of the delicate plant life, lest the local mountain goats will obliterate the latter in rabid quest for your urine salt (rather than harmlessly licking the rocks, which they do with enthusiasm). That’s also why salt had been, until large scale salt mining made it cheap, a highly valued commodity, in fact the origin of the word “salary”.
You actually need a fair bit of it. It is the eighth most abundant element in the human body (by numbers of atoms, or ninth by weight), and the average adult contains about 100grams of it. However, as it is also an important component of all other living things, which means there is always a good bit of it in any normal diet (and most abnormal ones).
I am not sure it is really the case that people or animals need extra salt in their diet, except in hot climates, where too much sodium tends to be lost through sweating, and through urination after drinking a lot of water. Of course, humans did evolve in such a climate, so perhaps that explains why we like the taste of salt.
The historical value of salt was not because of the nutritional need for salt, though. It was valuable primarily because it can be used to preserve foods prior to refrigeration. It was also valuable just because we like it (just look at the value of things like pepper in the same time period). Salt was useful as wages because it was universally desirable, making it easier to barter with than many of the other commodities of the time.