Newsletter #302

This week, I would like to circle back around to the topic of salt substitutes, since some new research has been released examining how these products work.

The evidence, overall, is impressive.

For example, when elderly people in care facilities were randomly assigned to have the salt in their meals replaced with a salt substitute, systolic blood pressure was reduced by 7.1 mm Hg and that group experienced a 40% reduction in cardiovascular events.

But why exactly do salt substitutes have this effect?

Salt substitutes, generally speaking, are composed of varying ratios of sodium chloride and potassium chloride (versus regular salt, which is 100% sodium chloride). Because salt substitutes are effectively replacing some of the sodium chloride with potassium chloride, they are doing two things at the same time: increasing potassium and lowering sodium.

The impact of sodium on blood pressure is fairly straightforward, although the specific mechanisms remain up for debate. However, we also know from randomized controlled trials that increased potassium intake lowers blood pressure, likely by facilitating sodium excretion through the kidneys.

So which of these is most important: lowering sodium, or boosting potassium?

A new analysis of one of the most influential salt substitute trials ever conducted tried to answer this question. Let's take a look.

The George Institute for Global Health in Australia conducted a large-scale randomized trial known as the Salt Substitute and Stroke Study (SSaSS). Nearly 21,000 older adults located in 600 villages around China were randomized to use either plain salt or a salt substitute (75% sodium chloride and 25% potassium chloride).

After five years, the participants who used the salt substitute had a 14% reduction in stroke risk, a 13% reduction in total cardiovascular events, and a 12% reduction in premature deaths, compared to those who used the regular salt.

To determine whether, and to what extent, sodium reduction or potassium augmentation might be responsible for the observed cardiovascular benefits of salt substitution, researchers went back and analyzed some of the data from the trial participants.

Specifically, they looked at 24-hour urinary sodium and potassium levels, which is regarded as the gold standard method for measuring intake of these minerals. This involves collecting every single drop of urine excreted over a 24-hour period. Needless to say, this is a pretty big ask for trial participants, but it is the best and arguably the only reliable way to gauge sodium and potassium intake.

They then combined this data with an array of external data sources which examined the dose-response relationship between changes in sodium and potassium and changes in systolic blood pressure.

In this way, they could estimate the level of systolic blood pressure reduction that you would expect, based on the urinary electrolyte levels that they saw in the trial, and then compare that to the actual observed changes in blood pressure that occurred.

Through these statistical models, they determined that 61-88% of the blood pressure lowering effect of the salt substitute could be attributed to the increase in potassium, rather than the decrease in sodium.

This is a particularly relevant finding in light of the modern food environment, and widespread consumption of ultra-processed foods.

You see, whole foods are naturally rich in potassium, and in theory it should not be difficult to consume 3-5 grams of potassium every day. However, modern processing techniques tend to reduce potassium from its constituent ingredients (while adding in sodium).

One important caveat worth mentioning here is that the baseline intake of potassium in this trial population seems to have been quite low.

Based on the urinary electrolyte data, it looks like they were consuming a little over 1400 mg of potassium per day at the start of the trial. To put that into perspective, most organizations currently recommend a minimum of 3500 mg of potassium daily. As a result of this meager baseline, the salt substitute increased their potassium intake by 57%, going from 1400 mg to 2200 mg per day.

This context matters because if you are already consuming a relatively high amount of potassium in your diet, then it's possible that the additional potassium in the salt substitute isn't going to make a very big difference. At that point, lowering sodium should become the more powerful lever with respect to regulating blood pressure.

That having been said, most Americans have plenty of room for improvement with respect to potassium intake. Research has found that the overwhelming majority — as many as 99% — fall short of the recommended intake of this mineral.

Finally, if you don't want to use a salt substitute, there are plenty of other options at your disposal. Some of the best dietary sources include root vegetables (potatoes, sweet potatoes, parsnips, etc), white beans, green leafy vegetables, avocados, bananas, etc. Beverages can be helpful here too. My favorite cheat code for getting potassium is drinking either celery juice or coconut water, both of which contain tremendous amounts of potassium. One bottle of coconut water, for instance, contains 810 mg of potassium with just 90 calories.

Salt has evolved into a bit of a public health menace, due to its ubiquity in processed foods and the impact of sodium on blood pressure. It’s easy to forget that at one time, it was a veritable savior.

In the early 1900s, goiter was widely prevalent, especially in regions with iodine-deficient soil. For example, a physician working for the draft board in Michigan during WWI reported having to reject almost 30% of US army candidates due to goiter and hypothyroidism. A statewide study of children during that time found that nearly half of kids had signs of serious thyroid dysfunction. Iodine deficiency is also linked to cognitive impairment, costing afflicted individuals as much as 15 IQ points.

Campaigns to use iodized salt almost fully reversed this issue:

“By 1935, the incidence of goiter in Michigan alone dropped by 74% to 90%, with the greatest decrease among children who had continuously used iodized salt for at least 6 months. Studies conducted in other goiter belt locations showed similar reductions.”

Morton Salt Company advertising blotter, circa 1925. From: University of Michigan Center for the History of Medicine.

As I’ve said before, I think the biggest barrier to adopting salt substitutes is palatability. Potassium chloride has a slightly metallic taste, which is why a lot of these products compromise by using a blend of sodium and potassium. I think this one strikes a pretty good balance. A single serving (1.4 g) contains 290 mg of sodium – which is about half the sodium content of regular table salt – along with 350 mg of potassium. Importantly, unlike a lot of salt substitutes, this one is also iodized.

Important caveat: Salt substitutes can be dangerous for those with kidney disease or who are taking certain diuretics, so you definitely should consult a doctor or pharmacist before using them.

This week, we’d like to highlight our How-to Guide for Smoothies. We know that consuming a nutrient-rich diet made up of fresh whole foods is key for performing at your very best, both physically and mentally. One efficient and convenient way to ensure that you’re making that happen on a daily basis is through smoothies. But obviously not all smoothies are necessarily a smart choice from a nutritional standpoint, which is why we developed this science-based guide to constructing healthy smoothies.

(By the way, smoothies are also a very easy way to ensure you’re getting plenty of potassium in your diet)

Wishing you the best,

https://mailchi.mp/humanos.me/newsletter-302