UCD nutrition study counters long-held belief

A recent study by two UC Davis nutrition professors shows that you needn’t be preoccupied with your sodium intake level – your brain already is.

“The brain exquisitely regulates sodium balance,” said co-author Judith Stern, a UC Davis nutrition professor.

The article, “Can Dietary Sodium Intake Be Modified by Public Policy?” which was published in October in the Clinical Journal of the American Society of Nephrology, found that humans innately regulate their sodium intake and dismisses governmental campaigns to lower sodium.

“The implications [of the study] are huge,” said the study’s author, David McCarron, a UCD adjunct professor of nutrition. “And they are that we have a public health policy that is moot, doesn’t matter, and yet for the better part of two decades, the food industry vilified for their sodium intake, running around trying to get it down and do what they’re told to do.”

The finding has outraged public health policy advocates, who have long preached the benefits of a low sodium diet.

“Not all scientists change when the science changes,” Stern said. “We’re all a bit guilty of that.”

McCarron began gathering sodium intake data in November 2008, in response to a challenge from Dr. Thomas Frieden, the commissioner of New York City’s Department of Health and Mental Hygiene to food company executives. He challenged the department to identify the foods that are contributing the most sodium to people’s diets and cut the level of salt by 25 percent over the next five years.

“By last February, I had most of it under control – I’d scoured the literature for government sponsored, carefully collected, properly designed, democratic samples around the world,” McCarron said.

After compiling data from approximately 20,000 adults in 32 countries, researchers concluded that adult sodium intake ranged from 2,700 to 4,900 milligrams per day. On its website, the Food and Drug Administration recommends that no more than 2,300 mg of sodium be consumed in a day – almost 15 percent less than the study’s lower limit.

“Even I was shocked at how tight this range was, because if you read Fast Food Nation, you’d think that humans are eating multiples of the quantity of salt that they ate 40 to 50 years ago, and that people are off the chart,” McCarron said. “If you look at the graph [of findings], that’s not true, there’s a very tight upper limit and a very tight lower limit.”

What makes these results stable, in addition to the sample size, is that each one of them is a multiple day sample. A 24-hour sample would show much more variability.

“The variability is because of that one person who will eat a whole cheese pizza in one night,” McCarron said.

Even someone who did choose to eat such a large amount of high sodium food would regain balance because of the strength of the human kidney, she added.

“As long as you don’t have serious kidney disease, you have an astounding capacity to excrete the salt, and you will,” McCarron said. “Because the connections between the heart, brain, intestine, kidney, etc. – the control points in the brain – are going to tell you to keep peeing it out.”

The kidney is a filter that runs at 80 to 100 milliliters per minute in healthy people, and if your brain tells the kidney to dump the circulating salt, it can do so in a hurry.

“But while you’re dumping it, there’s a tendency that you won’t go looking for that potato chip,” McCarron said. “You’re going to want to eat a few things that are lower in salt, and over four or five days you’re going to balance out.”

The most effective way to combat high blood pressure is to work with your physician to lose weight, Stern said, rather than eliminating sodium.

“If you can’t lose weight, or you put it back on right away, then you want to have a balance of calcium, potassium, magnesium and sodium,” she said.

Stern recommends the Dietary Approaches to Stop Hypertension diet, which emphasizes high servings of fruits and vegetables. But because even these perceived staples of a healthy diet contain salt, it proves the inevitability of sodium in the diet.

“Have you ever had broccoli without salt?” Stern asked. “A little bit of salt goes a long way to enhancing taste, and we wouldn’t be eating as many vegetables if we didn’t use salt.”

All that one can ask for as a nutritionist, Stern said, is balance.

“No one food provides everything – even Popeye couldn’t get it all from spinach.”

MIKE DORSEY can be reached at campus@theaggie.org.