Wednesday, May 22, 2013

The Problem With Salt Restriction

Every once in a while, you read something that just restores your faith in humanity. For me, a recent article in the New York Times did just that. Entitled "No Benefit Seen in Sharp Limits on Salt in Diet", the article makes the case that the latest sodium recommendations are too low, and that reducing sodium intake to such low levels could be dangerous.

Amen. It's about damn time. The newest sodium guidelines are ridiculously, stupidly, just absurdly low. How absurdly low you ask? The 2010 Dietary Guidelines set the upper limit at 2300 mg per day for healthy individuals, about one teaspoon of salt, and 1500 mg for those with hypertension or cardiovascular disease. Even more extreme, the American Heart Association feels that EVERYONE should shoot for 1500 mg. 

Maybe you don't know how low that is; if you've never tracked your sodium intake or read a food label then maybe you can't quite grasp it. So let me put it to you this way... the guidelines are so low, one study reports that only 0.12% of the population is eating a diet that meets the standards (1). That's 1 in every 833 of us! The average American eats about 3700 mg of sodium per day and has for the past 50 years (2). And our salt intake may have been even higher than that in the past (3). Hmm I wonder how we've all survived this long as a species when we're so blatantly overconsuming salt!?

Nope, these new recommendations just never made sense to me. But regardless of whether the guidelines are attainable, this New York Times article makes the case that a sodium intake that low can be downright dangerous. Interesting eh?? I thought so. So interesting that I spent the majority of my day at my food service rotation looking into it.

Salt is required for life.
The words "sodium" and "salt" are often used interchangeably. But in truth, they're not quite the same. Table salt is sodium chloride.  It's 40% sodium, 60% chloride, in fact, and both of these minerals are needed for life. Sodium is important for normal cellular metabolism and for maintaining proper fluid volume. It also plays a role in the nervous system, allowing neurons to transmit electrical signals. Without this function, we wouldn't be able to move or react to our environment, among other things. The chloride ions are needed for HCl (stomach acid) production, a necessary component of digestion and an important defense against food-borne pathogens (4). This biological need is manifested in the nature of living things... animals who are in a true salt-deficient state will seek out salty food and often consume far more salt than is needed to restore homeostasis (5).

The minimum amount of sodium required to sustain human life is estimated at 500 mg per day. But how much sodium is optimal? Well that's a horse of a different color (6). Let's start by looking at how healthy people respond to salt restriction.

Some of are salt-sensitive, some of us aren't.
An old study from 1987, a landmark study you could say, took a bunch of healthy men and women with normal blood pressure (normotensive) and hid their salt on them (7). They restricted their salt intake to 1600 mg a day, a very low level, for 12 weeks and tracked any changes in blood pressure. Here are the results...

Hmm... interesting. It's all over the map; some blood pressures went up, some went down, and some stayed the same. Not what you'd expect based on the mainstream media, right? Turns out, about 50% of us normotensives are salt sensitive, and we respond favorably to a low-sodium diet. But the rest of us? Some of us even increase our blood pressure on a salt-restricted diet! There were some notable trends as well... On average, the diet lowered blood pressure slightly.  Also, African Americans and older adults were the most likely to be sodium-sensitive.

When salt restriction goes wrong...
According to Dr. Michael H. Alderman, a dietary sodium expert who was referenced in the New York Times article, "As sodium levels plunge, triglyceride levels increase, insulin resistance increases, and the activity of the sympathetic nervous system increases. Each of these factors can increase the risk of heart disease." Sounds unbelievable doesn't it? I don't blame you for being skeptical; it's difficult to believe that salt restriction could be bad, based on all you've heard in the media. Surprisingly, though, there are a number of studies reporting adverse health effects with low-salt diets. Many of these were taken from Chris Kresser's fantastic series on salt (8). Hope you're ready for a research ride!

1.)  In patients with established cardiovascular disease or diabetes, intakes of less than 3000 mg or more than 7000 mg sodium per day were associated most strongly with cardiovascular events and hospitalization for congestive heart failure (CHF). Sodium intake of 4000-5999 mg per day is associated with the lowest risk of death (9). That is about DOUBLE the current "upper limit" of 2300 mg.

U-shaped curve: low salt intake and high salt intake are both harmful, while the optimal range lies in between
 (Note: sodium excretion is a marker of sodium intake)

2.)  Congestive heart failure patients were randomized into two groups, eating either a normal-sodium diet (2750 mg) or a low-sodium diet (1830 mg) for 180 days. And I quote... "The results of the present study show that a normal-sodium diet improves outcome, and sodium depletion has detrimental renal and neurohormonal effects with worse clinical outcome in compensated CHF patients. (10)"

3.)  Sodium intake was associated with a change in systolic blood pressure, but this did not translate into a higher risk for hypertension or cardiovascular disease. Lower sodium intake was associated with higher cardiovascular disease mortality (11). I repeat, the people who consumed the LEAST salt died the MOST.

4.)  In type 2 diabetics, those eating the least salt experienced higher rates of cardiovascular death and all-cause death. For every 2300 mg increase in sodium consumption, there was a 28% reduction in all-cause mortality (12).

5.) Healthy individuals were put on a low-sodium diet (okay very low, 500 mg) and a high-sodium diet (3500 mg) in random order for 7 days each. The low-sodium diet was found to increase insulin resistance, which can lead to type 2 diabetes (13).

Yes folks, it's true. Salt restriction may be unsafe. But more profoundly, following the USDA and AHA sodium guidelines may cause more harm than good. 

Despite all that, salt still matters.
Is there any benefit to a safe, moderate reduction in sodium intake? For the salt-sensitive folks, about 50% of us, a low-sodium diet may help reduce blood pressure. It might be a good idea for older adults and African Americans especially to watch their salt intake.

But there's still another compelling reason for sodium restriction that has nothing to do with blood pressure, hypertension, or cardiovascular disease... weight loss. As I've talked about many times, hyperpalatability and food reward is a major contributor to obesity (14). And one of the major factors that makes a food rewarding is saltiness. Although salt itself doesn't have any calories, it can lead us to consume more food than we really need, and that can be a problem. It's just easier to sit down and eat a lot of salty food than it is to eat a lot of low-salt food. Try it at home. For weight loss, salt restriction might be a good idea... but I'm talking about a moderate salt restriction here, maybe 2500 mg. I wouldn't want you to kill yourself at 1500. There's no need for that, and as you now know, it may even be dangerous.

So that's it for today, y'all. As always, keep it real and tell all your friends. And don't forget to enter your email over there on the right to stay up to date on all of my blog posts!

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