Dietary salt intake is typically linked with the impact that it has on blood pressure. Really, that has long been the only major concern I have had with higher salt/sodium diets.
Even that point is not relevant for everybody. Somebody who is quite far away from having issues with hypertension can typically have higher amounts of added salt without it really being an issue from a blood pressure perspective. Some people also seem more sensitive to sodium than others.
An interesting area of research that has developed recently is the effect of salt intake on gut health. It is very early on in the research, but sodium intake does clearly change the bacteria in our gut, which could have meaningful outcomes.
Healthy User Bias
When I first came across this concept through listening to other experts on the topic, my first assumption was that healthy user bias would be the major factor.
Healthy user bias is the concept of when somebody listens to one piece of health advice, they often listen to others. When somebody ignores a major public health message, they probably ignore others as well.
With sodium, it has long been a public health message to reduce salt intake.
It is safe to assume that people with higher salt intakes often also exercise less, eat more red meat, eat fewer vegetables, smoke more, drink more alcohol, get less sleep and probably live more stressful lifestyles.
My assumption was that these changes in gut health that experts were talking about were more likely to be related to those other factors than sodium intake alone. But looking at the research, salt intake actually seems like a factor that matters by itself.
Salt Reduces Lactobacillus, Which Then Reduces Butyrate
Lactobacillus is a population of gut bacteria that is typically considered “healthy.” It contributes to the production of health-promoting short-chain fatty acids such as butyrate, which is also linked with positive health outcomes.
One way around that healthy user bias issue I mentioned, is to conduct a controlled trial where the only variable this is changed is a change in sodium. And research group did exactly that.
The way they approached it was to provide 6g of sodium chloride tablets on top of the participant’s habitual diet. This was followed by stool samples.
After just 14 days of this, lactobacillus spp. was barely detectable anymore. There was a massive reduction in the amount of this good bacteria found in the stool sample.
In terms of how this could be relevant for overall health outside of blood pressure, low levels of lactobacillus populations have been linked with conditions such as inflammatory bowel diseases.
The Gut May Be Partly Responsible for Blood Pressure Regulation
As mentioned early, high salt intake is mostly linked to increased blood pressure.
Interestingly, this can be partly explained by mechanisms occurring in the gut.
Short-chain fatty acids (SCFAs) are often linked with “good gut health.” But they also play a role in blood pressure regulation.
SCFAs can influence the release of renin. This is an enzyme that plays a major role in controlling blood pressure.
A randomised controlled trial on 145 females with hypertension showed that reducing salt intake led to decreased blood pressure.
These participants had significantly higher blood levels of SCFAs following the reduction, which is part of the explanation for why this occurred. This helped increase what is known as arterial compliance – or more simply it allowed blood vessels to dilate more easily.
The reduction required for this to occur was to get down to 2000mg of sodium per day. The average intake for people in western countries appears to be around 3400mg per day, although some people go significantly higher than that.
Reducing from >4000mg per day to ~2000mg per day significantly increased levels of the SCFAs 2-methylbutryate, butyrate, hexanoate, is butyrate and valerate.
Although these SCFAs are not directly a marker of gut health, they are indirectly a marker due to being a by-product of the bacteria in your gut.
Gut-Health Supplements and Blood Pressure
If the link between gut health and blood pressure is this relevant, then of course it makes sense that people could be interested in skipping the salt part. Instead, theoretically, you could supplement with SCFAs or probiotics.
Supplementing with SCFAs for this purpose has been studied, but the result was underwhelming. It seems as though only about 2% of the supplemented SCFAs is absorbed, which is the explanation.
Instead, it makes sense to create an environment rich in healthy gut bacteria such as lactobacillus populations that produce SCFAs.
A meta-analysis on the impact of probiotic supplementation on blood pressure showed mild, but promising results. On average single-strain probiotics reduced systolic blood pressure by 4mmHg and diastolic by 2mmHg.
That does not look massive by itself. Multi-strain probiotics reduced it by 6mmHg and 3mmHg respectively on average, which is slightly more relevant.
Some individual studies have found even larger improvements, so it is worth exploring.
From my perspective though, the first step is focusing on overall gut health, rather than individual supplements.
Personally I do not put much stock into animal studies, for a variety of reasons.
It is worth being aware that there is a lot more animal data showing sodium intake affects gut health. Often, they are rodent studies showing significant reductions in SCFA production.
Typically, I prefer to wait for human data, and there really is not much more human data on this topic outside of what I have mentioned in this article at this stage. The best we can do is interpret the data we have got.
There is not a massive amount of human research on the impact of salt on the gut microbiome. This means it is hard to make interpretations on how relevant it is.
Aiming for less than 2000mg of sodium per day seems like a solid recommendation for most people. Those with hypertension probably would benefit from being stricter on it.
For those without hypertension, I would not overly focus on it, but I would still consider it one of many priorities. It would also contribute to another reason why it could be potentially detrimental to have an exceptionally high sodium intake.