A recent New York Times column offered us this provocative headline: Why Everything We Know About Salt May Be Wrong. Presumably that means- it may be right, too. Hence, my counter-headline.
I think what we know mostly is right. Here’s what I think we know:
Too much salt is bad for us. That one is almost tautological, since if it weren’t bad for us, it wouldn’t be too much.
Most of us consume too much salt. Most of the salt we consume- roughly 80%- is processed into foods we didn’t prepare ourselves. Eat less of those processed foods- especially hyper-processed foods, processed meats, and fast food- and more vegetables, fruits, whole grains, beans, lentils, unsalted nuts and seeds – and you’ll be better off for many reasons both related and unrelated to salt. Prepare meals at home from wholesome ingredients when possible and you’ll be better off. Drink plain water preferentially when thirsty- and you’ll be better off again. That’s what I think we know, and I think it’s all correct. If you like to get your punch lines and move on, our work here is done.
For the rest of you:
What we seem not to know about salt is the ideal intake level, and in particular, variations in that level based on age, health status, and genetics, among other factors. But we have long known that sodium is an essential nutrient, that we all need some, and that it’s possible to consume too much or too little. Debate about where best to draw the dividing line, and in particular whether it should be drawn in different places for different populations, is more a matter of refinement than refutation, evolution rather than revolution. It’s how science is supposed to advance.
The source of the new provocation presented to us in the Times is two research papers recently published in the Journal of Clinical Investigation, one involving mice, the other ten male cosmonauts in a simulated space environment. If that sounds like a somewhat dubious start to a dismissal of decades of research involving actual human beings, in much larger numbers, and subject to such pesky nuances as living in earth-like conditions, I’m inclined to agree. Mice and cosmonauts may teach us interesting new things about salt, but they are unlikely to reveal that everything learned to date is wrong.
Looking at the studies, they did no such thing. As acknowledged by the Times reporter, the papers are rather dense, enumerating a great many measures in recondite detail. For our purposes here, the gist will do.
The investigators found that both the ten healthy men in their simulated space station, and C57/BL6 mice are good at conserving levels of body water across a range of sodium intake. Complex hormonal fluctuations, some directly in response to diet and some part of underlying body rhythms, allowed for marked variation in the excretion of sodium (i.e., its removal in urine) without corresponding changes in urine volume. We have long known of the kidneys’ ability to concentrate or dilute urine over a wide but finite range, and these findings fit comfortably within that expanse of understanding.
Translating their own findings into succinct take-away messages, the researchers suggest that, in mice, “the kidneys, liver, and skeletal muscle form a physiological-regulatory network for extracellular volume control…” In plain English, the kidneys and other organs in the body work together, under the influence of various hormones,…