Dr. David Katz, Preventive Medicine: What we know about salt

Dr. David Katz

Dr. David Katz

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. I think what we know mostly is right.

Too much salt is bad for us. Most of us consume too much salt. Most of the salt we consume, or roughly 80 percent, 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.

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. The investigators found that both the 10 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. Fluid intake did not vary reliably with salt intake in the cosmonauts, but the more salt the cosmonauts consumed, the hungrier they tended to be.

The two studies are clearly valuable to the advance of science in this area. The finding that hunger varied with sodium intake in the cosmonauts far more reliably than thirst is particularly interesting. But the notion that the findings are an invitation to the general public to abandon all we thought we knew about salt intake is wrong, dangerous, and irresponsible.

It has long been clear that salty is a preferred flavor sensation that stimulates appetite. While sweet is the one flavor preference known to be innate, a predilection for salt comes easily, early, and all but universally. The salience of this in modern food processing, and its relevance to efforts by Big Food to maximize how much eating we all do, and thus their profits, is addressed in considerable detail by Michael Moss among others, in his book: “Salt, Sugar, Fat.”

While it is somewhat surprising that salt fostered hunger more than thirst in the cosmonauts, I’m not sure that precludes the prospect of it doing both in the real world. At any given bar stool, tasty, salty snacks fairly reliably invite eating; perhaps it’s that eating as much as the salt per se that tends to invite concomitant drinking.

The Center for Science in the Public Interest attributes hundreds of thousands of premature deaths to excess sodium intake in the U.S. A recent study in JAMA, stunningly unmentioned in the Times column, examined dietary factors associated with chronic disease and premature death at the level of the entire U.S. population. The single dietary factor associated with the most cardiometabolic death was: excess sodium intake.

The misrepresentation of any one study, small group of cosmonauts, or batch of mice — and the incremental advance in understanding they contribute — as a replacement for all we knew prior is a pernicious theme in modern health journalism that wounds public health. Hyperbolic headlines propagating unfounded positions and misapprehensions put salt in those wounds. Among the things I thought we knew about salt, I thought we knew we certainly shouldn’t do that.

Dr. David L. Katz ;www.davidkatzmd.com; founder, True Health Initiative