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Salt is a compound made up of about 40 percent sodium and 60 percent chloride. Sodium is an essential nutrient, but vegetables and other natural foods provide the small amounts of sodium you need in your diet. If you consume too much, it can cause water retention, and your body may respond by raising your blood pressure to push the excess fluid and salt out of your system.

For the first 90 percent of human evolution, we likely ate diets containing less than the equivalent of a quarter teaspoon of salt’s worth of sodium a day. Why? Because we likely ate mostly plants. We went millions of years without saltshakers, so our bodies evolved into sodium-conserving machines. That served us well until we discovered that salt could be used to preserve foods. Without refrigeration, this was a boon to human civilization, but where does that leave us now? After all, we no longer have to live off pickles and jerky.

Humans seem to be genetically programmed to eat ten times less sodium than we do now. Many so-called low-salt diets can actually be considered high-salt diets. That’s why it’s critical to understand what the concept of “normal” is when it comes to sodium. Having a “normal” salt intake can lead to a “normal” blood pressure, which can contribute to us dying from all the “normal” causes, like heart attacks and strokes.

If we could cut our salt intake by about a half teaspoon a day, which is achievable by avoiding salty foods and not adding salt to our food, we might prevent 22 percent of stroke deaths and 16 percent of fatal heart attacks. That’s potentially more lives saved than if we were able to successfully treat people with blood pressure pills.

The evidence that sodium raises blood pressure is clear, including double-blind, randomized trials dating back decades. If we take subjects with high blood pressure and put them on a sodium-restricted diet, their blood pressure drops. If we keep them on the low-salt diet and add a placebo, nothing happens. However, if we instead give subjects salt in the form of a time-release sodium pill, their blood pressure goes back up again. The more sodium we give them secretly, the higher their blood pressure climbs.

Even just a single meal can do it. If we take people with normal blood pressure and give them a bowl of soup containing the amount of salt that may be found in an average American meal, their blood pressure climbs over the next three hours compared to eating the same soup without any added salt. Dozens of similar studies demonstrate that if you reduce your salt intake, you may reduce your blood pressure. And the greater the reduction, the greater the benefit may be. But if you don’t cut down, chronic high salt intake can lead to a gradual increase in blood pressure throughout life.

How did we first learn of this? Enter Dr. Walter Kempner and his rice-and-fruit diet. Without drugs, he brought patients with eye-popping blood pressures like 240/150 down to 105/80 with dietary changes alone. How could he ethically withhold medication from such seriously ill patients? Modern high-blood-pressure pills hadn’t been invented yet! Dr. Kempner conducted his work back in the 1940s. He was able to reverse the course of disease with diet in more than 70 percent of cases. Though the diet wasn’t merely extremely low sodium—it was also strictly plant-based and low in fat and protein—Dr. Kempner is now recognized as the person who established, beyond any shadow of doubt, that high blood pressure can often be lowered by a low-sodium diet.

In addition to high blood pressure, salty meals can significantly impair artery function, even among people whose blood pressure tends to be unresponsive to salt intake. In other words, salt itself can injure our arteries independent of its impact on blood pressure. And that harm begins within thirty minutes.

Image Credit: Amanda Rae. This image has been modified.

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