Eating healthier food can add almost 10 percent to the average American's food bill -- and that is just to boost a single nutrient like potassium.

Researchers from the University of Washington looked at the economic impact of following new U.S. dietary guidelines, which recommend eating more potassium, dietary fiber, vitamin D and calcium, and avoiding saturated fat and added sugar.

The diet recommendations try to fight rising rates of obesity in the United States, but the study findings underline some of the obstacles to adopting new habits.

In an article in Health Affairs published on Thursday, the researchers reported that eating more potassium, the most expensive of the four nutrients, can add $380 to the average person's yearly food costs.

Americans spend about $4,000 on food each year, according to the U.S. Department of Agriculture.

At the same time, getting more calories from saturated fat and sugar reduces overall food costs, the study said.

Pablo Monsivais, acting assistant professor at the University of Washington and one of the study's authors, said the government should consider the economic impact of food guidelines.

"We know that dietary guidelines aren't making a bit of difference in what we eat and our health overall," he said. "And I think one missing piece is that they have to be economically relevant."

"They emphasize certain foods without much regard for which ones are more affordable."

More than one-third of children and two-thirds of adults in the United States are overweight or obese.

In the study, the authors collected questionnaires on the typical eating habits of 1,123 people in King County, Washington, and calculated how much each diet cost based on retail food prices in three local supermarkets.

However, they did not factor in costs for food bought outside grocery stores, such as fast food -- which would likely increase the food cost for each person.

The study also found that it is more expensive to eat more dietary fiber and vitamin D, and that people with higher average incomes were more likely to eat healthier food.

Monsivais said when talking about eating more fruits and vegetables, the government should also mention the most cut-price options. For examples, bananas and potatoes are the cheapest sources of potassium.

"(Guidelines) should tell people where you get the most bang for your buck," he said. "By putting the economic dimension on dietary guidelines, it would be very helpful for those on the economic margins, but also for everyone ... trying to save money in the current economy."