Scientific American ran an interesting interview last week with Marion Nestle, one of the magazine’s board members and a professor of nutrition, food studies and public health at New York University.
They asked her to explain the “salt wars” — the ongoing uncertainty and controversy about whether excess salt (or, more precisely, sodium) in the diet leads to high blood pressure and heart disease. There have been dueling studies on this issue, and the findings have been highly contradictory.
As the article points out, both sides have accused the other of being “delusional” about the evidence.
Who’s right? We may never get a good answer because we may never be able to conduct a good study, Nestle says. She cites several reasons. To begin with, “so much salt is added to the food supply and … so many people eat out, it’s impossible to find a population of people who are eating a low-salt diet,” she says. “They basically don’t exist.”
Then there’s the problem that not everybody responds to a low-salt diet.
“There’s a proportion of people in the population who are sensitive to salt — if you lower their intake of salt, then their blood pressure goes down,” Nestle explains. “There’s another (probably larger) percentage of the population who doesn’t respond. They are people who can eat as much salt as they want and still their blood pressure is low. So you have this curious anomaly where whenever you do a clinical trial you get these complicated, difficult-to-interpret results that don’t show much of an effect.”
Another problem has to do with people’s taste for salt.
“If you’re on a low-salt diet it takes three to six weeks to get accustomed to being on a low-salt diet,” Nestle says, “and then everything you eat tastes salty.”
But, since 80 percent of the salt we eat comes through processed foods, getting people accustomed to a low-salt diet is, well, challenging at best. Nestle points out that Campbell Soup announced last week that its low-sodium “Select Harvest” soups have been selling so poorly that they’ve decided to put the salt back in.
Many experts believe that the public’s taste for salt won’t change without a huge public-health effort — an effort that would require regulating the amount of salt in processed foods and in restaurants. Nestle says she’s for such an effort, but she’s also realistic about the politics around it.
“I think everybody would be healthier if they ate less salt [less even than the current 1,500 milligrams a day currently recommended only for individuals with strong risk factors for heart disease],” she says. “You can always add salt if you don’t think it’s salty enough, whereas I can’t take it away if it’s presented to me. And that’s the dilemma. And the ferocity of the arguments gets into the whole question of personal responsibility and ‘nanny state’ and all of these other enormous debates that really don’t get at the public-health question. And the public-health question is hard to resolve because the science is really difficult to do.”
You can read the entire interview with Nestle on Scientific American’s website.