Homo sapiens‘ intake of salt has skyrocketed over the most recent millenia, reaching shocking, unprecedented levels. A growing body of evidence indicates that this influx of sodium chloride into the human diet not only is at the center of the etiology of the hypertension epidemic, but that it has also contributed to driving up the incidence of a number of other disorders, including various gut and immune-related pathologies.
A while back, I posted an article here on the site in which I talked about this issue. In the time that has passed since then, researchers have further examined the relationship between dietary salt, gastrointestinal function, and immunity, and it has become increasingly clear that high-salt diets wreak havoc on the gut and immune system, and by implication, undermine the health and vitality of the whole organism.
Why all this fuss about salt?
I’ve written extensively about salt here on the site this past year. Part of the reason why I’ve devoted so much attention to this white substance is that I discovered some time ago that a significant number of health & fitness aficionados, including some associated with the evolutionary health community, appear to operate under the belief that it’s unproblematic, or even healthy, to consume quite a bit of salt. I’d also noticed that certain book authors and bloggers were pushing the idea that the war on sodium is scientifically unfounded; that salt, in the grand scheme of things, is largely benign; and that a number of people may actually benefit from taking in more salt, as opposed to less.
I was somewhat surprised, bordering on perplexed, by these observations, as I consider the case against salt to be close to air-tight. If anything, I believe the dangers of salt consumption have been underestimated, not overestimated, and that’s saying quite a bit, seeing as various nutritional authorities and public health agencies have loudly expressed concerns regarding the blood pressure-raising effects of sodium and urged people to limit their consumption of salty foods.
Salt is a ubiquitous part of our current nutritional environment; hence, it’s obviously important that people are aware of how it affects them, so that they have the option of modifying their behavior accordingly. Coupled with the fact that some people have recently proposed that salt should be vindicated, this helps explain why I’ve devoted so much attention to this white substance recently.
With that said, let’s get onto the topic at hand…
How high-salt diets affect the gut and immune system
In a recent article, I mentioned that one of the main reasons why I personally limit my intake of salt is that I’ve noticed that it destabilizes my gut and brain. Even small increases appear to cause perturbations and make me feel inflamed. This isn’t particularly surprising in light of the scientific data pertaining to the gut and immune related effects on salt consumption that have emerged over the most recent years.
A few weeks back, a new review paper that summarizes what we’re learned to date was published in the medical journal Nephrology Dialysis Transplantation. Here’s the gist of the article, which is entitled Emerging evidence of an effect of salt on innate and adaptive immunity:
Salt intake as part of a western diet currently exceeds recommended limits, and the small amount found in the natural diet enjoyed by our Paleolithic ancestors. Excess salt is associated with the development of hypertension and cardiovascular disease, but other adverse effects of excess salt intake are beginning to be recognized, including the development of autoimmune and inflammatory disease. Over the last decade there has been an increasing body of evidence demonstrating that salt affects multiple components of both the innate and adaptive immune systems. (1)
Given that our immune systems are inter-linked with the microorganisms that occupy our bodies, it’s reasonable to assume that the immune-related effects of salt consumption are somehow associated with gut microbiota alterations. This has been shown to be the case, as highlighted by the quote below, pulled from a recent review paper on the topic:
The present literature review concludes that HSD [a High Salt Diet] not only plays an important role in some autoimmune diseases, but also, by initiating innate and adaptive immunity, breaks the gut immune homeostasis, participating in the progress of common GI [Gastrointestinal] diseases. (2)
The gut microbiota undoubtedly mediates some of the immune related-effects of salt consumption. That said, as pointed out in the above quote, gut microbiota alterations can also occur secondary to immune perturbations. This really goes without saying, as our immune systems contribute to shaping the composition of the microbial ecosystems we harbor.
Salt appears to induce differentiation of CD4+ T cells into TH 17 cells – a subset of T helper cells defined by their production of the proinflammatory cytokine interleukin 17 (IL-17) (3, 4). TH 17 cells are involved in defense against pathogens at mucosal sites, which leads me to think that their emergence following the consumption of salt probably relates to the effects that salt has on the gut microbiota. TH 17 cells have been implicated in a variety of autoimmune disorders and inflammatory conditions, including psoriasis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and asthma (5, 6, 7); hence, it seems plausible that they are at the center of the connection between dietary salt and immune dysregulation.
Seeing as pretty much everything that goes on in the human body is affected by the state of the microbiota and immune system, it goes without saying that the physiological effects of excessive salt consumption are going to be widespread, affecting everything from the brain to the pancreas to the bones.
It’s important to note that when scientific researchers embark on the process of examining how a particular type of substance affects our health, they typically collect and administer quite a lot of the substance in question. What I mean by that is that they expose the subjects of their studies to fairly large quantities of the compound that’s under scrutiny, in part because this ensures that any potential effects will be clearly detectable. If you only give very small doses of something, the effects of the exposure, if any, are likely going to be negligible. Also, it’s important to point out that many nutritional experiments are performed in animal models. This is important to keep in mind when one interprets the results of scientific research, including research pertaining to the effects of salt consumption.
What constitutes a normal or healthy salt intake for humans?
Notwithstanding the caveats mentioned above, the case against salt is fairly clear cut. Several dose-response relationships have been established. Moreover, a very compelling body of research points to the conclusion that we’re genetically adapted to low-salt conditions (8, 9, 10, 11, 12, 13). This research spans multiple decades and encompasses consistent and coherent findings regarding the evolution of the human diet and biology. It’s clear, from a Darwinian standpoint, that it’s perfectly safe and healthy to eat a diet that is very low in sodium chloride, as highlighted by the quote below:
Human beings were genetically set up to survive and reproduce under conditions of low Na and high K dietary intakes, which sharply contrast with modern diets that are rich in Na and poor in K. (8)
One doesn’t even have to look into the scientific literature to understand that this has to be the case; all one has to do is to quickly examine the nutritional content of whole, unprocessed, and unsalted foods (e.g., fruits, vegetables, meat, fish). Such foods are inherently low in sodium; hence, it goes without saying that we’re evolutionarily accustomed to eating a low-sodium diet. People who eat an unsalted, unprocessed whole foods diet will by default take in little sodium.
Together, these findings clearly refute the idea that the injurious effects associated with salt consumption only emerge at very high intake levels and that it’s generally better to take in some added salt (e.g., 5-7 grams a day) than little or no added salt.
Last words and primary takeaways
The high salt content of modern convenience foods arguably represents one of the greatest nutritional threats to humans. This threat is ignored or underestimated by some people, in part because salt constitutes a fairly small portion of the foods we eat, and consequently also our diets (a typical westerner takes in about 10 grams of salt a day, which may not sound like much). Furthermore, it doesn’t have the same direct effect on our waistlines as sugar and fat.
What a lot of people don’t know is that a daily salt intake of 10 grams (or 5 grams for that matter) represents an extreme outlier in evolutionary regards. Such an intake falls way above the evolutionary norm for our species. Furthermore, it’s not common knowledge, at least not yet, that the consumption of salty foods doesn’t just predispose us to hypertension, but also to a variety of other problems, including autoimmunity and gut dysfunction.