At first glance, the University of Iowa seems to have done fast-food lovers a big favor.

UI scientists have declared that giving french fries a good dusting of salt actually helps control any weight gain that might be associated with downing, say, McDonald’s 510-calorie large portion of the highly popular side order.

The scientists found that salt on the high-fat food item prevented mice from gaining weight.

But before you order a second load of fries, the scientists would like to remind you that salt can cause health problems in humans. If you use the salt shaker like there’s no tomorrow, you may not have a tomorrow. The seasoning, at very high levels, contributes to cardiovascular disease in humans.

So the UI scientists say the message here is less “Whoopee, give me the Super Size!” and more of a level-headed finding that noncaloric dietary nutrients seem to have an unexpected effect on energy balance and weight gain.

That’s science-speak for, “We thought both the fat in the fries and the salt would make you fat. We were wrong.”

“People focus on how much fat or sugar is in the food they eat, but [in our experiments] something that has nothing to do with caloric content — sodium — has an even bigger effect on weight gain,” says Justin Grobe, assistant professor of pharmacology at the UI Carver College of Medicine. He co-authored the study, which was published in the journal Scientific Reports June 11.

The scientists fed groups of mice diets that varied in fat and salt content. They found that the mice on the high-fat diet with the lowest salt gained the most weight, while animals eating the most fat and salt had low weight gain.

“We found out that our french fry hypothesis was perfectly wrong,” Grobe said. “The findings also suggest that public health efforts to continue lowering sodium intake may have unexpected and unintended consequences.”

“This suppression of weight gain with increased sodium was due entirely to a reduced efficiency of the digestive tract to extract calories from the food that was consumed,” Grobe said.

The study was funded in part by grants from the National Heart, Lung and Blood Institute, the American Diabetes Association, and American Heart Association.

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