A new study published in the Canadian Medical Association Journal suggests that depending on where you live, you may be consuming more salt when you eat fast food.
According to the study, "The salt content of fast foods varies substantially, not only by type of food, but by company and country in which the food is produced." Both the study's authors and the media covering the research have used the new data as a springboard for discussing how to reduce salt consumption, which is thought to be good for public health. But is it?
However obvious a conclusion it may seem, the evidence justifying a low salt diet is rather limited. And though the debate will likely continue, there is decent evidence which suggests that dietary sodium, even a lot of it, is perfectly safe for most people.
The recommendation to reduce salt intake is based on a number of observational studies linking sodium consumption to heart attacks, strokes, and other serious medical conditions. What's often not reported about this research, however, is that there are also studies that find no ill effects associated with higher salt intake. Some studies even find that people who consume more salt may live longer. And still more research suggests that low salt intake may increase insulin resistance and the risk of death due to cardiovascular disease for diabetics. In short, the observational data are all over the place. Nobody can fairly judge the benefits of reducing dietary sodium from these studies.
The clinical research does not prove the low salt hypothesis either. Not one clinical trial conducted has confirmed the suggestion that population-wide reductions in sodium consumption will improve public health. Inconvenient facts like these have led some scientists to urge caution; they suggest that it may be better to wait for more evidence before telling everybody that salt will kill them. A 2011 review of the research on dietary sodium reductions published by the highly respected Cochrane Collaboration agreed, concluding that scientists "... do not know if low salt diets improve or worsen health outcomes."
One way to find a satisfactory answer to the question about dietary sodium is to broaden the search. Many scientists have argued over the last 50 years that conditions like hypertension and heart disease are the result of increasing amounts of sugar and other carbohydrates that have made their way into our diets, not sodium (see here and here for more about that). The theory here is that too many carbohydrates prompt the kidneys to hold onto salt rather than excrete it. According to Gary Taubes in Good Calories, Bad Calories, removing the carbohydrates works similarly to drugs called diuretics, which cause the kidneys to excrete sodium as well as water. The result is lower blood pressure and the health benefits that go with it. Unlike the ambiguous evidence for dietary sodium as a cause of hypertension and heart disease, multiple studies conducted in recent decades have provided support for this minority position.
Of course, none of this means that fast food is especially healthy. But there are ingredients far more deserving of scorn than salt. The vegetable oils many fast food restaurants use to cook french fries and other fried foods, for example, can wreak havoc on human health in a variety of ways. The sugar-laden sodas McDonald's offers for just a dollar definitely aren't slowing down obesity and are surprisingly similar to alcohol. There's also the refined carbohydrates found in hamburger buns, hash browns, and chicken batter to consider, which just about everybody concedes are harmful.
Given the available evidence, it appears that the concern over dietary sodium is misplaced. Chances are it's perfectly safe for consumption, though nobody really knows for certain just yet. Either way, there's not enough evidence to scare consumers out of eating salt.