Food labels that say ‘low salt’ or ‘no fat’ may be misleading, suggests a new study.

These ‘low-content’ claims are based on comparisons with other foods and are not standard definitions. Making such a claim doesn’t necessarily mean the food is more nutritious than other brands, the authors say.

Consumers should “turn the package around and look at the entire nutritional profile as well as the ingredients list in order to get a better sense of whether the product overall is healthier or less healthy,” Lindsey Smith Taillie of the University of North Carolina at Chapel Hill told Reuters Health in a phone call.

Smith Taillie and colleagues analyzed data on more than 80 million food and beverage purchases made in the United States by 40,000 families from 2008 to 2012.

“We found that higher-income households tended to be more likely to buy products with these types of claims, which is consistent with previous research that suggests that claims tend to be more utilized by people with higher levels of education,” Smith Taillie said.

As reported in the Journal of the Academy of Nutrition and Dietetics, 13 percent of food and 35 percent of beverage purchases included products with some type of low-content claim. Low-fat purchases were the most common, followed by low-calorie, low-sugar, and low-sodium claims.

On average, packaged foods with low-nutrient claims had 32 percent fewer calories, 11 percent less sugar, and about half the fat and sodium compared to foods that didn’t carry any claims on the packaging.

However, some products with low-nutrient claims actually had more of that substance than foods without those claims.

Also, Smith Taillie said, when a product has a low-sugar claim, for example, it might have less sugar than a reference product or a similar product, “but it doesn’t mean that it has an overall better nutritional quality.”

Or, “it could be a high-sugar food but be low in fat, so it’s going to say low fat on the label. That doesn’t mean that it’s healthy,” she said.

“Essentially, it can be kind of misleading to make a decision about a product based on a front-of-package claim,” she added.

The U.S. Food and Drug Administration regulates what products can claim, Smith Taillie said.

“It’s not that the products are technically wrong in making a low-content claim, it’s just that the rules that allow them to make this kind of claim vary by the claim and by food category,” she said.

Food labels can be confusing, agreed Melissa Rifkin, a dietitian with Montefiore Medical Center in New York City who was not involved in the study.

Understanding what a nutrition fact label means is more important than focusing on marketing claims,” Rifkin told Reuters Health by email.

Key items to focus on are serving size, quantity per container, calories, fat, sodium and sugar, she said.

A new and revamped nutrition fact label is under development, Rifkin said.

“Slowly we will begin to see all labeling take on the new information,” she said.