Salt Intake on a Low-Carb Diet
If you've looked around much trying to figure out about the best salt intake, you may have run into some controversy. Generally we've gotten the message for the past 30-40 years that when it comes to salt, "the less the better." But now that dogma is being challenged. Let's take a look at the controversy and also address a separate question as to how eating a low-carb diet could affect the amount of salt we need.
How Much Sodium Is Recommended?
As of July 2015, (before the 2015 Guidelines were released) the Dietary Guidelines for Americans said that the "general population" should restrict their intake of sodium to 2300 mg (about a teaspoon of salt). However, about half the population is not apparently in the "general population," as people over 50, African-Americans and others in groups at a risk for high blood pressure were told to restrict their intake to 1500 mg. The American Heart Association maintained that everyone should stay at 1500 mg. (By the way, no one does this. Basically, it's really difficult to do! So we could have a conversation as to whether it's a good idea to recommend something that only a vanishingly small number of people worldwide attain. But instead, let's turn to the science.)
What Good Does it Do to Limit Salt?
The reason it is recommended to limit salt intake is that there is an association between eating a lot of salt and high blood pressure.
However, there are a couple of caveats:
1) While going from a high-salt intake to a moderate-salt intake does tend to lower blood pressure, for most people going from a moderate intake to a low intake does very little good. After looking into the matter, in 2013 the Institute of Medicine reported that there is no evidence that reducing sodium intake below 2300 mg provides benefit.
Other recent analyses have shown little correlation in the general population between blood pressure and salt intake, although there are definitely people who do benefit, which brings us to:
2) The people who benefit the most from salt reduction are what is called "salt sensitive," which is thought to be about 10-20 percent of the general population. Older people, African-Americans, and people who have high blood pressure are more likely to be salt sensitive.
If you are salt sensitive, it is probably good to know it, although the only real way to find out is to wait until you have high blood pressure and then see if reducing salt helps. But there is actually evidence that people who are salt sensitive are at a greater risk for heart disease even if their blood pressure is kept normal. One thought is that whatever is causing the salt sensitivity may be causing inflammation and possibly other bad effects. We still have much to learn about this.
What Is a Moderate Salt Intake?
There is lots of controversy on this point!
Some experts say that the average amount of sodium people tend to eat (around 3500 mg, or 3.5 grams) is way too much, while others say that this is the very definition of moderate. I've seen experts who say that up to 5 or 6 grams of sodium per day is still moderate intake, although they all add that above this is too much.
Are You Eating Too Much Salt?
If you cook from scratch and mostly eat at home, you are probably eating a moderate or lowish amount of salt by any definition. But if you eat out a lot and/or eat prepared and packaged foods, the grams can add up fast! According to the Centers for Disease Control and Prevention, the average person in the United States gets about three-quarters of their sodium from restaurants, prepackaged, and processed foods, while only 5 percent is added during home cooking and 6 percent from the salt shaker at the table.
Fast Food Example: Wendy's Quarter Pound Cheeseburger: 1220 mg of sodium (290 of that is in the meat patty, 330 in the bun, 390 in the cheese, and the rest in the condiments). I'm not picking on Wendy's, BTW — almost all chain restaurants have numbers like this.
Are There Dangers From Too Little Salt?
This is an area that has not had much research, but some of the preliminary work is concerning. Some observational studies (many of them self-report) have shown increased "cardiovascular mortality" or "all-cause mortality" for people eating a low-salt diet, but it's hard to tell what complicated interactions may be part of this. For example, sick people may eat less food, which automatically means they eat less salt.
To remedy this, some researchers in Australia took a group of people with type 2 diabetes who were instructed to keep salt intake low (most had high blood pressure). They were followed for 10 years. You can tell how much salt a person is eating by collecting their urine for a 24-hour period, and these people were monitored in this fashion several times over the 10-year period. Results: The lower the salt intake of the participants, the higher their risk of dying! Both cardiovascular mortality and all-cause mortality were higher in the people who ate the least amount of salt.
Why could it be dangerous to eat too little salt? Well, blood and many other bodily fluids (lymph, sweat, and the fluid around our organs) are fairly salty, for good reasons. Our bodies use sodium (and chloride, the other component of salt) in lots and lots of ways, and it's easy to imagine that things could go awry if we don't have enough of it. One of the more interesting observations is that a low-salt diet could increase insulin resistance in the muscles of some people. The researchers of the diabetes study point out that interference in metabolic and neurohormonal pathways that could result from a low-salt diet, at least in some people, but admit that we know very little at this point.
Salt Intake and Low-Carb Diets
Could eating a low-carb diet impact our need for salt? Some experts think so (again, at least in some people). Particularly in the first two weeks of a very low-carb (ketogenic) diet, the body lets go of a lot of water, and some electrolytes such as sodium and potassium along with it. Some physicians who are familiar with working with low-carb diets in their patients actually advise their patients to consume more salt during this time to help mitigate the "Atkins flu" — feeling sickly in the first week or so. They often advise drinking a couple of cups of boullion or broth each day during this time.
Other experts, notably Stephen Phinney and Jeff Volek, feel that people on long-term ketogenic diets may need more salt on an ongoing basis, particularly if they are athletes or very active. They point to evidence that people on ketogenic diets tend to excrete more sodium. In The Art and Science of Low Carbohydrate Living, they advise that such people add 2-3 grams of sodium to the diet each day, particularly if they are feeling lightheaded or poorly with exercise. (I personally have never felt I needed extra salt, but I'm not a heavy exerciser.)
What Should We Do?
As those of us who benefit from low-carb diets know very well, recommendations from the government or large health organizations are not always the best for the individual! It's up to you to find out what works for you. Make sure your blood pressure gets checked. Stay away from processed foods. If your blood pressure is high, make sure you're following a healthy low-carb diet, which has been shown to help normalize blood pressure for many people. If that doesn't do the job, try cutting back on salt.