University of California-Davis nutrition researchers are challenging the decades-old conventional wisdom that we should watch our salt.
The controversial article, published this week in the Clinical Journal of the American Society of Nephrology, found that humans naturally regulate their sodium intake, rendering government intervention useless.
It's a study that has angered nutrition policy advocates; one went so far as to call the study "junk." But co-author David McCarron, an adjunct UC-Davis nutrition professor, said it is backed by sound data and that he expects such a left-field finding to get heat.
The study concluded that the human body makes sure sodium levels remain within a certain range at all times, similar to bodily functions that are homeostatically maintained, such as body temperature.
"Our sodium intake is regulated by the brain, and your brain won't let you go very far outside of that boundary," McCarron said. "You may eat that whole bag of chips, but it just means that as you sit down you'll unconsciously go toward foods that are lower in sodium."
After aggregating sodium intake data from 20,000 adults in 32 countries, researchers found the adult range of sodium intake to be narrow: between 2,700 to 4,900 milligrams of sodium a day. Because the data encompasses many different dietary cultures, researchers concluded that humans, on their own, maintain a "normal" range of salt intake.
"There looks to be a pretty darn strict lower and upper limit on sodium levels," McCarron said. "Just because our food supply is filled with sodium doesn't mean it's ending up in our bodies."
Furthermore, the authors concluded that the U.S. Food and Drug Administration guidelines are too stringent. Current FDA dietary guidelines recommend no more than 2,300 mg of sodium be eaten per day, which is 14.8 percent lower than the study's observed lower limit.
Co-author Judith Stern, a nutrition professor at UC Davis, said lawmakers should instead focus on more pressing public health issues, such as childhood obesity.
"They need to work on setting priorities," she said.
The study's findings are scientifically plausible, said Christopher D. Gardner, an associate professor at Stanford Medical School.
"But as a consumer, I don't believe it," he said. "If you laid out a bunch of foods in front of me and they were highly processed with sodium, I don't think I would stop eating them once I had reached my sodium limit."
The findings are in stark contrast to what doctors and public health researchers have long preached: A low-sodium diet is important for reducing blood pressure and risk of heart disease and strokes.
Michael Jacobson, executive director of the Center for Science in the Public Interest, a Washington, D.C.-based nutritional advocacy group, said the study is doing public health a disservice.
It's ridiculous to say that humans cannot lower their salt intake, because most of our excess salt intake is from processed foods, he said. Certain tribes have been known to consume less than 1,000 mg of sodium per day, and several European countries have been successful in getting residents to lower salt intake, Jacobson said.
"All experts agree that our current levels of sodium intake are causing heart attacks and strokes," he said. "This study is really an outlier."
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