We only think we know the truth about salt, argues Gary Taubes, author of “Why We Get Fat,” in an opinion piece for The New York Times called “Salt, We Misjudged You.”¯ Excess salt is supposed to be bad for us. The maximum recommended sodium intake per day is 2,300 milligrams for healthy individuals; for those who have or are at risk for hypertension, it’s 1,500 milligrams. On average, Americans consume 3,700 milligrams of sodium per day.
The Department of Agriculture, the Centers for Disease Control and Prevention, the American Medical Association and leading public health experts continue to urge Americans to reduce their sodium consumption to avoid hypertension, heart disease and premature death. But the science on salt linking it to hypertension has always been “weak”¯ and “flimsy.”¯ Taubes explains:
In 1972, when the National Institutes of Health introduced the National High Blood Pressure Education Program to help prevent hypertension, no meaningful experiments had yet been done. The best evidence on the connection between salt and hypertension came from two pieces of research. One was the observation that populations that ate little salt had virtually no hypertension. But those populations didn’t eat a lot of things — sugar, for instance — and any one of those could have been the causal factor. The second was a strain of “salt-sensitive” rats that reliably developed hypertension on a high-salt diet. The catch was that “high salt” to these rats was 60 times more than what the average American consumes.
Even as researchers acknowledged that the data was “inconclusive and contradictory” or “inconsistent and contradictory,”¯ the campaign for sodium reduction was born. After all, the national program Taubes references was founded to advise Americans on measures that could be taken to prevent hypertension, so researchers had to come up with something.
Some studies, like the 2001 DASH-Sodium trial, suggested that cutting back on salt does lower blood pressure, but there is no conclusive evidence showing that it also moderates hypertension. Yet, in the American consciousness, the link between salt and hypertension is strong, and it has become conventional wisdom, however misguided, that one of the best ways to fight hypertension is by reducing salt consumption.
Reducing salt consumption, in fact, may hurt more than help us, as new evidence that has emerged over the past two years suggests. In fact, the same year that the NIH introduced the National High Blood Pressure Education Program, Taubes writes, “The New England Journal of Medicine reported that the less salt people ate, the higher their levels of a substance secreted by the kidneys, called renin, which set off a physiological cascade of events that seemed to end with an increased risk of heart disease. In this scenario: eat less salt, secrete more renin, get heart disease, die prematurely.”
Whether experts advise us to eat less or more salt may not matter in the last. A Harvard study, published in the November 2010 issue of The American Journal of Clinical Nutrition, found that salt intake is about the same today as it was nearly 50 years ago, in spite of the 40-year-old campaign to reduce Americans’ salt consumption. The study was based on the amount of salt tested in the urine of 26,000 participants between the years 1957 and 2003. (The urine test is a more reliable measure than is self-reporting of what and how much participants ate in a day.)
As USA Today reported at the time, “researchers thought they would find that salt intake had increased over time because Americans eat more processed foods today than in 1957. But decade after decade, people consistently consumed about 3,700 milligrams of sodium a day.” Rates of high blood pressure, on the other hand, have gone up in the past 20 years, suggesting that “America’s ever-rising obesity rates may play a more critical role in this rise than salt intake.”
Additional studies showed that salt consumption among various populations in more than 30 countries also remained stable over time. What’s remarkable is that every one of these populations consumed roughly 3,700 milligrams of sodium per day. As one researcher put it, “it’s spooky how consistent this number is.” “This consistency,” Taubes writes, “suggests that how much salt we eat is determined by physiological demands, not diet choices.”
So the science against salt, to say the least, is shaky. For the food industry, which has been criticized for the abundance of sodium it uses in its formulations of processed foods, the news is cause for celebration. But, to be clear, the fact that it may be okay to eat more salt than indicated by official guidelines is not an endorsement for eating more processed foods. Processed foods are to be avoided for many other reasons. The verdict on salt, on the other hand, is under review.
Photo Credit: Happy Krissy
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