For years, health authorities around the world have warned people that they are eating too much salt.
So who’s right - the people, or the health authorities? The question sounds naive, but in fact, some scientists ask the very same thing, and it lurks behind the debate that has sprung up this year over the government’s longstanding salt advice, which is embedded in the U.S. Dietary Guidelines.
At a major scientific conference last week in New York City, some presenters suggested that, in fact, the persistent global appetite for salt might be a sign that humans are geared for more salt than health authorities would allow.
These scientists point to new science indicating humans may be hard-wired to crave salt, and that there may be a natural appetite for it above the amounts that the government recommends. They point to the vast gap between what the authorities say is a healthy amount of salt and the amounts that people around the world are actually consuming.
The U.S. official warning on salt is “the most radical existing nutrition recommendation,” said Niels Graudal, a researcher at Copenhagen University Hospital, at the New York meeting of the American Society of Hypertension.
The U.S. Dietary Guidelines currently advise people to eat less than 2,300 milligrams sodium per day, or roughly the amount that comes in one teaspoon of salt. Americans, meanwhile, consume much more than that - about 3,500 milligrams per day. Around the globe, salt consumption is above the U.S. guidelines, too - the averages ranges from 2,500 milligrams per day to 4,500 milligrams per day, according to surveys.
Not surprisingly, scientists who support government efforts to reduce sodium consumption dispute the idea of a natural appetite for high levels of salt. They say that the reason people are eating so much salt is that the corrupt modern diet makes it all too available in processed foods, especially bread.
“Our salt taste preferences are based on what we commonly eat and what we’re used to,” said Mary Cogswell, a CDC scientist. Cogswell said that since she has switched to a low-salt diet, she often finds food at restaurants too salty.
“Our need for salt is entirely hedonistic – that is, it is a pleasure but it kills you,” Graham MacGregor, a medical professor at Queen Mary University of London, and a long-time supporter of salt restrictions, said by email.
Either way, as the federal government prepares its influential Dietary Guidelines for 2015, bureaucrats must take a side in what has become a profound and heated scientific debate: They must either retract the government's longstanding salt warning, which is echoed by the American Heart Association, or they must overlook recent studies suggesting that the government advice on salt, far from helping people, might even be dangerous for the otherwise healthy.
Even some of the major health associations are now divided on the question. Earlier this month, the Academy of Nutrition and Dietetics, the largest organization of food and nutrition professionals, issued a statement expressing their concern about the science behind government’s salt advice.
“There is a distinct and growing lack of scientific consensus on making a single sodium consumption recommendation for all Americans," said Academy President Sonja L. Connor. She cited the research indicating that the low sodium consumption recommended by the government is “actually associated with increased mortality for healthy individuals.”
Exactly what is a “natural” level of salt in the diet has been a matter of debate for decades.
Early on in the debate, some scientists suggested that the natural level of salt consumption is very low, and as evidence, they pointed to some remote hunter-gatherer societies that subsist on very low levels of salt. Those peoples suffer less from cardiovascular disease. But as critics pointed out, those populations may be far too different from most of modern society to make useful comparisons.
Now some scientists are proposing just the opposite - that the "natural" level of salt consumption is higher than the government advises. Their evidence is the global surveys showing the consistently high levels of salt consumption, seemingly regardless of socioeconomic status.
“All over the world, people tend to eat a consistent amount of sodium that isn’t super high and isn’t really low,” said Joel Geerling, a researcher at Beth Israel Deaconess Medical Center in Boston. “That doesn’t happen by chance in biology.”
The question this raises, of course, is whether this level of salt intake is somehow dictated by the human body.
Some of Geerling’s research may shed some light. For several years, he and his colleagues have been studying the brain activity in mice and rats that have been deprived of salt. In doing so, they have identified specific neurons that fire when an animal has a saltless diet.
“What our work did was put a group of neurons on the map, showing neurons that fire when you take salt out of the diet,” Geerling said. “When the animal drinks saline, those neurons stop firing, very quickly, within an hour.”
That circuitry could be the basis of a natural salt appetite in humans, and there’s at least some evidence that this natural appetite would lead animals to eat salt in amounts above the very bare minimums required for living.
For one thing, this circuitry appears to be active, at least at low levels, even when animals have been getting more than minimal amounts of salt, Geerling said. Moreover, separate research by Graudal and others indicates that when people eat the low levels of sodium recommended by the government, their bodies produce renin, a hormone that may have harmful effects on blood vessels.
So are we built to be eating salt in amounts higher than the government recommendations? Like other questions in the salt debate, there is yet no definitive answer. And even if there is some salt appetite wired into the brain, that doesn't necessarily mean that satisfying those cravings would be good for you.
But with the evidence so murky, some scientists are questioning the wisdom of the public health campaigns pushing people to alter their salty diets.
"I cannot see why the society should spend billions on sodium reduction," Graudal said.