The Great Salt Debate | The Body of Evidence

The Great Salt Debate

There's been a lot of controversy recently about whether we should abstain from salt. In fact the debate is getting louder and angrier with little concensus. The evidence is not as contradictory as some think and industry involvement is certainly coloring the issue, but overall the great salt debate can be summed pretty easily. Don't add salt to your food.

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Given the number of people who have asked me about this recently, the salt controversy shows no signs of abating anytime soon. If anything, the fight over the “salt hypothesis” is becoming increasingly divisive and nasty.

For the past few decades, the general agreement has been that high salt diets contribute to hypertension. Salt is a molecule composed of sodium and chloride. Sodium is an ion that is essential for the proper functioning of nerves and muscles. But eating too much sodium in the form of table salt can lead to medical problems.

First, the more sodium you consume, the more water you retain. So, for anyone with congestive heart failure or kidney disease, retaining water can lead to swelling and water on the lungs.

High sodium intake can also lead to high blood pressure. Interestingly, not everyone is equally sensitive to the effects of sodium. Older individuals, those who already have high blood pressure, those who are obese or have metabolic syndrome all seem to be more sensitive to salt than the general population. Genetics also seem to play role, as salt sensitivity is more common in people of African ancestry.

But not all the research is in agreement. Studies in the past few years have cast doubt on the “salt hypothesis,” including a Lancet study from McMaster University that suggests low sodium intake might actually increase the risk of cardiovascular disease. There are two problems with the study.

First, researchers didn’t measure salt intake. They measured the sodium excreted in the urine. And while that’s an accepted research tool, it only correlates with other more robust measurements about 60-70 per cent of the time. 

Second, the low-sodium group comprised only a sliver of the total population (10 per cent overall, and less than three per cent after statistical adjustment). Achieving very low sodium intake is practically impossible, since sodium is omnipresent in most living things. It’s also important to point out that despite its iconoclastic hype, the study did show that a high-sodium diet increases risk of heart attack and death.

The problem with the debate over salt is that it’s becoming polarized.

A review in the International Journal of Epidemiology found that most research supports the salt hypothesis, but an important minority does not. More worrying, though, is that this difference of opinion is descending into tribalism, with little communication between opposing camps.

The analysis found that researchers frequently only cite research that agrees with their position and discount anything that contradicts it. The discussion around the paper proved to be equally caustic. The “non-believers” point to a review from Cochrane, an independent health research network. The review was inconclusive and offered up only weak evidence for a benefit.

The “believers” point out that much (but not all) of the research that fails to show a benefit for salt reduction was funded by the food industry, which has a vested interested in the outcome. In a quippy editorial in the epidemiology journal, John Ioannidis offered up an insightful commentary, pointing out that science isn’t about belief or non-belief, but about facts. And sometimes we have to acknowledge uncertainty.

We can be pretty certain that a diet high in salt is bad, while I think there is some uncertainty over whether diets very low in sodium pose a risk. But from a practical standpoint, few people will ever achieve such an extremely low sodium diet. Thus, it seems pretty reasonable for people, especially the elderly, those overweight, and those with high blood pressure, to avoid excessive salt, to not add it to their plate, and to minimize its use during cooking. I prefer to use garlic to flavour my food. I’m not sure if it really helps with blood pressure. But at least it keeps away the vampires.

Christopher Labos is a Montreal doctor who writes about medicine and health issues.

Christopher.labos@mail.mcgill.ca 

twitter.com/drlabos