The salt debate rages on outside these halls, but I’ve never really opened MDA’s doors to the tempest (beyond a short dalliance several years ago). Today, though, I am. We’ve likely all consumed a fair bit of sodium chloride over the past holiday weekend, and I imagine a few of us are wondering whether that’s a problem or not. Ever timely, reader John has written in with his salt story and a simple question: how much salt is suitable for humans?

Here’s his question:

I went Primal last year, and I’m down about 25 to 30 pounds and blood pressure is lowered. I have definitely followed your advice on low salt. For example, if I buy tomato sauce or paste, I get the “No Salt”, and I buy the low salt cashews, preferably with sea salt. What do you think about this new research that has come out, saying that salt is not that bad for you, and that it’s not actually related to heart disease? Just wanted your take.

John

There’s a lot of back and forth on salt, even among mainstream researchers. It used to be that dietary salt was absolutely evil, that it would spike your (everyone’s!) blood pressure and cause certain heart attacks and stroke. I mean, your average health-conscious grandparents probably still eat all their foods unsalted because, along with egg whites and 1% milk,  that’s just how you ate when you were trying to lower blood pressure and reduce the risk of an early death. But then stuff like the research to which John is most likely referring rolls around: this study (from the Cochrane Review in the American Journal of Hypertension) that Scientific American featured in its recent story, “It’s Time to End the War on Salt.” In fact, salt is kinda like the new egg. Will it or won’t it (kill you/clog your arteries/give you cancer/enter nefarious-sounding characteristic of necessary dietary component here)?

First of all, outright demonization of an element as important as sodium is silly and foolish. We literally have a physiological requirement for sodium (about 500 mg per day), and we come equipped with sensory apparati on our tongues (taste buds) specific to salt and extant for the express purpose of identifying salty things so we can consume them. It’s obvious that salt is necessary, and that it’s not poison. In fact, it:

• Supports the nervous system – both sodium and chloride (also known as sodium chloride, or salt) are necessary for the firing of neurons.
• Regulates blood pressure – keeps it from going too low or (usually) too high.
• Helps maintain acid-base balance and blood volume.
• Supports the function of the adrenal glands which produce dozens of vital hormones, including the stress and sex hormones.

But how much is too much? Is there such a thing as a limit to sodium intake?

Loren Cordain thinks the amount of salt average Americans get daily – almost 10 grams, or 3,875 mg of sodium – is excessive and evolutionarily discordant as indicated by the earliest evidence of salt mining by homo sapiens coming from China in 6000 BC and Spain in 6200 BC, well after the advent of agriculture. In his paper, he acknowledges the likelihood that coastal dwellers “may have dipped their food in seawater or used dried seawater salt,” but doesn’t find that the totality of evidence supports high sodium intake by humans during the Paleolithic. While I agree with 10 daily grams of refined salt being evolutionarily discordant and possibly excessive for some people, I think he’s overlooking something.

There’s plenty of evidence that the earliest humans were largely coastal dwellers with a fondness for seafood – particularly shellfish, which are rich in sodium. As I wrote in that shellfish post, basically any culture with coastal access left behind ample evidence of constant shellfish consumption. Some researchers are even suggesting that a bottleneck in human evolution occurred sometime between 190k and 130k years ago, when the total human population was reduced to about a thousand individuals living on the coasts of South Africa, eating a diet rich in seafood and especially shellfish. If it is from those thousand-odd humans that every current living human descends, and they were big shellfish eaters, I’d say it’s pretty likely that we can tolerate a decent amount of salt.

According to the USDA database, three ounces of raw clams, oysters, and mussels provide 510 mg, 90 mg, and 243 mg of sodium, respectively. I even think they’re undercounting the sodium content of oysters, personally. I regularly eat raw oysters on the half-shell, and there’s no way that mouthful of briny goodness contains just 90 mg of sodium. I’m guessing they measured the oysters rinsed and cleaned and from a jar, rather than slurped straight out of the shell. If our direct ancestors (all of them, assuming this bottleneck occurred) ate steady amounts of salty seafood straight out of the shell/sea, then salt can’t be bad, right?

Kinda. Some people are genuinely “salt-sensitive.” When they consume higher levels of salt, their blood pressure increases. When they drop the salt intake, their blood pressure drops with it. Studies indicate that of patients with hypertension, 51% are salt-sensitive (73% of African-American hypertensives are salt-sensitive), while 26% of normotensive patients are salt-sensitive. And since we know sodium chloride plays a physiological role in the regulation of blood pressure, this isn’t controversial in the least. But the majority of randomized controlled trials have been inconclusive regarding the effects of salt on hypertension, as the Cochrane Review mentioned, and some studies have found a slight increase in disease from “low-salt” diets. Another found “normal sodium” diets resulted in better outcomes for congestive heart failure patients than “low sodium” diets (less followup hospitalizations and certain blood markers). The evidence is mixed and murky, for sure.

That said, there’s way more to blood pressure than just salt intake. Like:

• Fructose. Yes, fructose is strongly linked to hypertension. One study found that omitting one 12-oz sugary drink per day lowered BP. Dietary fructose increases salt absorption by the kidney, thus suggesting a synergistic effect between fructose and salt intake; you ditch the sugar and maybe the salt isn’t such an issue. Of course, salty and sweet often accompany each other in the industrial food world, probably to the kidney’s ultimate detriment.
• Or potassium. Some research indicates that the dietary potassium:sodium ratio is more important than the absolute level of sodium in the diet. Although Ned Kock suggests that it may just be another marker for a healthy diet rich in real food.
• Or general processed food intake. I’ve discussed this before, but consider that processed food accounts for most of the sodium in the average person’s diet. As one survey of the worldwide dietary sodium scene found, over 75% of sodium intake in North America and Europe comes from manufactured food. Asian countries consumed twice as much sodium on average than other regions, but consumed less processed food. I think it’s plausible that sodium intake is often just a proxy for processed food intake in epidemiology, and that’s partially explaining the rise in hypertension – not just the salt alone (although that obviously plays a role in certain individuals’ hypertension).
• Or stress. Psychosocial stress is a likely cause of hypertension, even among people with low-salt diets. Well-adjusted, socially-fulfilled lab rats don’t get hypertensive on high-salt diets, while Malawi adults on low-salt diets get hypertensive when exposed to modern stressors.

The simple answer is that there is no one simple answer regarding the health effects of salt. It’s clear that while salt intake alone does not determine blood pressure for everyone, or even most, a certain portion of the population appears to be salt-sensitive; in this population, sodium intake increases blood pressure and decreasing intake decreases it. The genetics of salt-sensitive hypertension are complicated, undoubtedly with different epigenetic triggers and environmental contexts for the various manifestations, and experts are still mulling over specific recommendations in 2011.

I have a few somewhat specific recommendations, however:

Rather than obsess over the amount of salt in your diet, focus on eating enough potassium-rich foods, avoiding excessive fructose, and managing your stress. These will do more for your heart health, blood pressure, and overall enjoyment of life than measuring out 1/8 teaspoons of salt. You think calorie counting is bad? Try sodium ion counting!

Avocados, sweet potatoes, chard, and most fruits are excellent sources of potassium. Work those things into your diet, if they fit your template.

So’s meat, actually, particularly red meat. Just be sure to eat your meat closer to rare than not, as raw meat contains more potassium than cooked meat. And let your steak rest before slicing into it after cooking; the potassium’s (and flavor’s) all in the juice!

Don’t be scared of reasonable amounts of fruit, especially if you’re active; just avoid refined sweets and excessive amounts of excessively sweet fruit.

Pay attention to how you’re feeling. If I have lots of cured meats or salty cheeses or I eat out on the road several days in a row, I start feeling kinda… not great and somewhat bloated and heavy. On the other hand, sometimes I feel genuine cravings for salty food. In both cases, I listen to my body.

If you’re interested, run your meals through a Fitday or a Cronometer or something similar, and track your sodium, potassium, and fructose intakes.

Try to eat considerably more potassium than sodium, but through food (at least a 5:1 ratio). We like to point out how sodium might just be a proxy for processed food intake, but the same could be said for potassium intake, which might just be a proxy for real food intake. Consuming a refined diet with no vegetation or fresh meat but supplemented with potassium salts probably isn’t the same as consuming a real diet with actual food containing ample potassium (though potassium salts subbed for regular salt has been shown to reduce blood pressure in hypertensive patients with naked tails). And whether it’s the potassium or the lack of sodium or the real food providing the benefits, eating the real food and using real salt when applicable while avoiding processed and sweetened junk will get you there.

As for determining whether you need to reduce sodium intake, it’s pretty simple. If you have elevated blood pressure (and it’s not just white-coat syndrome) and you are salt-sensitive, reducing salt intake should lower blood pressure over the course of a few weeks. Cut your salt intake by around half to test for salt sensitivity. A quarter teaspoon in the meal instead of a half teaspoon, unsalted butter instead of salted butter – that sort of thing. Nothing super rigorous, just a general reduction in sodium. Increasing your potassium intake will “confound the results,” but this isn’t some stiff objective study on strangers you’re running; this is your life and your health, so don’t worry too much about eating that avocado cause it’ll throw off the effect of a reduction in salt intake.

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