French fries. Popcorn. Peanuts.
All taste better with a sprinkling of salt. And all will make you thirsty.
Turns out that added salt might also make you hungry.
A recent study turned some scientific beliefs on their little salty heads, according to Dr. Jens Titze, associate professor of medicine and molecular physiology and biophysics at Vanderbilt University, and the report’s senior author.
The results were published as a two-paper set in the Journal of Clinical Investigation earlier this month.
Working in collaboration with scientists in Germany, the Vanderbilt team looked at what happens in the body 18 to 24 hours after the intake of salt.
“Everybody believes that if you eat salty stuff, you’ll drink more,” Titze told Healthline. “But the body adjusts to a higher salt intake. Over 18 hours, there’s water generation in the kidneys. The body produces more water, so you are less thirsty.”
Salt and water
According to conventional wisdom, excreting dietary salt inevitably leads to water loss into the urine. As a result, there is a reduction in body water content.
Surprisingly, that’s not what the researchers found.
Instead, they showed that the biological principle of salt excretion is actually water conservation and water production.
In essence, the body maintains its own water balance, Titze said.
Normally, he said, about 70 percent is excreted in our urine. The rest goes through the lungs or elsewhere.
“For instance, if it’s warmer, you’d sweat more,” Titze noted.
The researchers expect the findings might provide new insights into the Western epidemics of obesity, diabetes, and heart disease.
“We have always focused on the role of salt in arterial hypertension. Our findings suggest that there is much more to know — a high salt intake may predispose to metabolic syndrome,” Titze said.
“We had a big problem with what we found,” he added. “Nephrologists believe what goes in must go out. Yet urine output decreased.”
Using cosmonauts for research
In order to study what happens to salt in the body, it is necessary to control what goes in and what comes out, something rather difficult to do in most populations.
So, between 2009 and 2011, the scientists conducted long-term sodium balance studies in Russian cosmonauts who were participating in a human space flight simulation program at a research facility in Moscow.
“We needed subjects where we could collect every crumb and every urine drop,” Titze noted.
Unexpectedly, when dietary salt was increased from 6 to 12 grams per day, the men drank less water, not more. That suggested they conserved or produced more water.
A subsequent study in mice found that high salt induces a catabolic state driven by glucocorticoids that breaks down muscle protein, which is converted into urea by the liver. (Urea enables the kidneys to reabsorb water and prevent body water loss while the salt is excreted.)
In effect the body cannibalizes itself in order to provide more water.
That cannibalization naturally makes a person hungry.
In addition, increased levels of glucocorticoids are an independent risk factor for diabetes, obesity, osteoporosis, and cardiovascular disease.
Whatever other treatments come from this discovery, Titze is convinced people need to radically reduce their salt intake.
“It’s easy to cut your food intake by 35 percent,” he said. “If you eat only two-thirds of each meal that would reduce salt, too.”
The one-third plan runs a bit contrary to what’s happening out in the field.
Kristin Kirkpatrick, a registered dietitian and manager of wellness nutrition services at Cleveland Clinic, is author of the recently published book “Skinny Liver.”
“I'd rather teach about what foods to eat than to just eat less of any food, but I can see the rationale in this advice as limited to 70 percent reduces all components of that food,” she told Healthline.
For Kirkpatrick, the solution is to “Eat real food, and make your diet at least 70 percent plant-based.”
“If you eliminate most foods from a box, you can avoid a lot of sodium in the diet,” she said.
Nevertheless, Kirkpatrick found the study interesting. “It represented an aspect of sodium we had not seen before. Dehydration can be confused with hunger.”
“I don't think it changes any guidelines for diabetes, heart disease, or obesity, however,” she added. “There are plenty of studies from the past few decades that show that too much sodium in the diet increases chronic disease risk, especially heart attack and stroke. Perhaps if anything it may provide even more motivation for individuals with diabetes and obesity to limit sodium even further.”