Book update: It’s still safe to ignore salt

 

Hey, I saw there was another big salt study that just came out1.

That’s right. Now there’s even more evidence that worrying about salt is a waste of time.

But people do seem to worry about it quite a lot.

Yeah, well, what can I tell you? People do a lot of things that don’t really make any sense.

Oh, c’mon, is it really that clear cut?

Yeah, it is. Especially given the results of this new study. I mean, first principles, animal experiments, and human experiments all point in the same direction2

Can you walk me through it again?

Sure. So it’s clear that high blood pressure is bad, right?

Right. If my blood pressure is high, that means my heart is working really hard, which might cause it to fail eventually.

Right. And the high pressure can damage the walls of your blood vessels and make it easier for fat packages to get stuck and for plaques to build up.

Right. So high blood pressure is bad. And the idea is that eating a lot of salt will increase my blood pressure, so, therefore, salt is bad, right?

That’s the idea. The problem is that it’s not really true.

Why not?

Well, if your blood pressure is normal and your kidneys are working properly, then eating more salt is not going to increase your blood pressure, at least not significantly. It’s really critical that the amount of salt in your blood stays constant, so if you eat more salt than you need, your kidneys will filter it out into your urine.

Oh, right, and when my kidneys are working properly, they can easily filter out more salt without increasing my blood pressure. But when my kidneys aren’t working properly, then the only way to get them to filter out more salt is to push my blood through them really hard, which means increasing my blood pressure.

Exactly.

OK, so if my kidneys aren’t working properly and my blood pressure is high, then I should eat less salt, right?

Oh, sure, if you already have high blood pressure and you’re eating a ton of salt, then, yes, of course you should eat less salt. But as the kids like to say, no duh!

Yeah, I don’t think the kids say that any more.

Whatever. Anyway, the problem is that there are these blanket recommendations for all people to reduce salt across the board, which are distracting at best, and downright harmful at worst.

Why would eating less salt be harmful?

Because salt is one of the key chemicals in your body, and you can’t make it yourself. So if you don’t eat enough of it, you’re going to have problems. The amount of salt suggested in most of the official dietary guidelines is way too little – it’s actually associated with an increased risk of health problems. Fortunately, very few people actually follow those guidelines. Which is not surprising, because you have strong, hard-wired mechanisms in body and brain that are designed to make sure you eat enough salt.

OK, so what did this new study show?

Well, believe it or not, this was the first time anyone thought to check whether the health risks associated with eating salt were different for people with and without high blood pressure.

And what did they find?

Just what you would expect – for people who don’t already have high blood pressure, there is no link between salt and death, or heart attacks, or anything like that. Except, of course, for the increased risk associated with eating too little salt.

So people who ate more salt didn’t actually have any more health problems?

No. In fact, if anything, they had fewer.

OK, but that’s for people who don’t already have high blood pressure. What about people who do already have high blood pressure?

Again, it’s just what you would expect. For people with high blood pressure, eating either too little or too much salt increases risk.  

And that’s because if you already have high blood pressure, it’s probably an indication that your kidneys aren’t working properly, which means that eating too much salt will drive your blood pressure up even further, because the only way to get the extra salt out will be to push your blood through your kidneys even harder.

Exactly. So, yes, if you have high blood pressure and you eat a lot of salt, then you should try to cut back. But that’s an obvious point. The only way you can really eat too much salt is by eating processed foods. So if you have high blood pressure and you’re eating a lot of processed foods, you should stop. Again, no duh!

Right. And why didn’t anyone notice this difference between people with and without high blood pressure before?

I don’t know. I guess because no one thought to look for it. When you look at the health risks associated with eating salt for all people together, all you really see is the pattern for people with high blood pressure.

Why?

Well, if you’re looking at how salt is related to the risk of something like heart attacks, the results will be dominated by people with high blood pressure because they are the ones having most of the heart attacks. So if you have want to see what’s going on in people without high blood pressure, you have to separate them out first.  

Right. And you think all of this was already clear from first principles?

Sure. Our ancestors lived in an environment in which food sources were scarce and unreliable, so the amount of salt that they ate varied a huge amount from day to day and week to week. Given that cells only work properly when the amount of salt in them is just right, the only way our ancestors could survive the variation in their salt intake was to evolve a system that would keep only the amount of salt that was needed and filter out the rest. Obviously, we still have that system, so it shouldn’t really matter how much salt we eat, unless the system is no longer working properly.

Right, but …

Hold on. This assumes, of course, that we are talking about diets that are mix of mostly unprocessed foods. If you’re eating a lot of processed foods with a lot of salt, and you’re forcing the system to deal with amounts that are way above those that is was designed for, then all bets are off. But if you’re eating a lot of processed foods, salt is just one of the many problems that you’re going to have.

OK, I’m with you. So since I’m pretty healthy and I eat mostly unprocessed foods, I can just ignore salt altogether?

That’s right.

And it’s not going to come back to haunt me?

Nope.

OK, I hope you’re right …

 

1. Mente, A., O’Donnell, M., Rangarajan, S., Dagenais, G., Lear, S., McQueen, M., Diaz, R., Avezum, A., Lopez-Jaramillo, P., Lanas, F., et al. (2016). Associations of urinary sodium excretion with cardiovascular events in individuals with and without hypertension: a pooled analysis of data from four studies. The Lancet.

2. O’Brien, E. (2016). Salt—too much or too little? The Lancet.