 For the first 90% of our evolution, we ate diets containing less than a quarter teaspoon of salt a day. Because for the first 90% of our evolution, we ate mostly plants. We went millions of years without salt shakers. And so our bodies evolved into salt-conserving machines, which served us well until we discovered salt could be used to preserve foods. Without refrigeration, this is a big boon to human civilization. Of course, this may have led to a general rise in blood pressure, but who cares if the alternative is starving to death because I saw your food rotted away? But where does that leave us now, when we no longer have to live off pickles and jerky? We are genetically programmed to eat 10 times less salt than we do now. Even many low-salt diets can be considered high-salt diets. That's why it's critical to understand what the concept of normal is when it comes to salt. Having a normal salt intake can lead to a normal blood pressure, which can help us die from all the normal causes, like heart attacks and strokes. Doctors used to be taught that a normal systolic blood pressure is approximately 100 plus ages. Systolic blood pressure means the top number. And indeed, that's about what we're born with. Babies start out with a blood pressure around like 95 over 60. But then as we age, that 95 can go to 120 by our 20s, then 140 by our 40s, the official cut-off for high blood pressure, and keep climbing as we age. That was considered normal, since everyone's blood pressure creeps up as we get older. And if that's normal, then heart attacks and strokes are normal, too, since risk starts rising once we start getting above the 100 we had as a baby. But if blood pressure is over 100 or associated with disease, maybe they should be considered abnormal, perhaps caused by our abnormally high-salt intake, 10 times more than what our bodies were designed to handle. If we just ate a natural amount of salt, our blood pressures naturally would not go up with age, and we'd be protected. Of course, to test that theory, you'd have to find a population in modern times that doesn't use salt or eat processed food or go out to eat. For that, you'd have to go deep into the Amazon rainforest. Meet the Yanamamo people, a no-salt culture. Lowest salt intake ever reported, which is to say normal for our species salt intake. And so what happens to their blood pressure? They start out with a blood pressure of about 100 over 60, and end up with a blood pressure of about 100 over 60. Though theirs is described as a salt-deficient diet. That's like saying they have a diet deficient in Twinkies. They're the ones that seem to be eating normal salt intakes, apparently leading to truly normal blood pressures. Those in their fifties having the blood pressure of a 20-year-old. The percentage of the population tested that had high blood pressure? Zero. Whereas elsewhere in Brazil, up to 38% of the population may be affected. The Yanamamo's probably represent the ultimate human example of the importance of salt on blood pressure. But look, it could have been other factors. They didn't drink alcohol, ate a high-fiber plant-based diet. Lots have exercised no obesity. There's a number of plant-based populations eating little salt that experience no rise in blood pressure as they ate. So how do we know what exactly is to blame? Ideally, we do an interventional trial. I mean, imagine if you took people literally dying from out-of-control high blood pressure, so-called malignant hypertension, where you go blind from believing into your eyes, your kidneys shut down, your heart fails, and then you withhold from those people blood pressure medication. So their fate is certain death. And then you put them on a Yanamamo level of salt intake, a normal for human species salt intake. And if instead of dying, they walked away cured of their hypertension, that would pretty much seal the deal. Enter Dr. Walter Kempner in his rice and fruit diet. Patients coming in with blood pressures of 210 over 140, dropping down to 80 over 60. Now the reason he could ethically withhold all modern blood pressure medications and treat with diet alone? The drugs hadn't been invented yet. This was back in the 1940s. Now the diet wasn't just extremely low salt, but strictly plant-based, extremely low fat protein calories. But there's no doubt that Kempner's rice diet achieved remarkable results, and Kempner's now remembered as the person who demonstrated beyond any shadow of a doubt that high blood pressure can often be lowered with a low enough salt diet. 40 years ago, it was acknowledged that the evidence is very good, if not conclusive, that a low enough reduction of salt in the diet would result in the prevention of essential hypertension, that rising of blood pressure as we age. And its disappearance is a major public health problem. It looks like we knew how to stop this for decades ago. In that time, how many people have died? Today, high blood pressure may wipe out 400,000 Americans every year. 1,000 unnecessary deaths every day.