Hardly a day passes without a new study, and an ensuing round of headlines, sounding the alarm on ultraprocessed foods.

This wide-ranging category — including sodas, processed meats and many breakfast cereals, snack foods, frozen meals and flavoured yogurts — has been linked to a range of health issues such as obesity, type 2 diabetes, heart disease, gut conditions and depression.

So it may come as a surprise that when a committee of 20 of the US’s leading nutrition scientists met in late October to preview their recommendations for the next edition of the Dietary Guidelines for Americans, they said that there was not enough evidence to steer people away from the foods.

New limits on ultraprocessed foods, which make up a large share of what US children and adults eat, could dramatically shift Americans’ diets, experts say. The dietary guidelines are used to set standards for federal food programmes and inform how doctors counsel their patients about nutrition.

The US Department of Agriculture and the Department of Health and Human Services will ultimately issue the guidelines, which are slated for release by the end of 2025.

Part of the committee’s job was to review the research on ultraprocessed foods and then summarise those findings in a report they will submit to the federal agencies by this December.

The expert committee was specifically tasked with evaluating whether ultraprocessed foods had any influence on body composition (like fat mass
or waist circumference) or on the risk for obesity in children and adults.

In the 41 studies they reviewed — more than half of which were on children and adolescents — the experts found a relatively consistent link between ultraprocessed food consumption and a greater risk of becoming overweight or developing obesity.

But the committee cited a few serious concerns about the quality of the research, including that many studies were conducted outside of the United States, where ultraprocessed foods might be formulated differently.

Another issue was that many of the studies were based on diet records that were collected from participants decades ago, so the researchers had to make educated guesses about which foods were ultraprocessed and which were not.

Most of the studies included in the review were also observational, meaning they couldn’t prove cause and effect in the way that clinical trials can.

These concerns with the research led the committee to conclude that the evidence linking ultraprocessed foods to obesity was too limited to make a recommendation on them.

Instead, the committee focused their recommendations on those that had more robust research to back them, such as emphasising diets centred on vegetables, fruits, legumes, whole grains, low-fat or non- fat dairy products, and fish or seafood. They did say that people should limit their consumption of processed meats and sugar-sweetened beverages — two products that are included in the ultraprocessed category, and have very clear links to chronic disease.

Marion Nestle, a professor emerita of nutrition, food studies and public health at New York University in the US, said that in her view, the committee set too high a bar for the studies they included in their review and left out important evidence on ultraprocessed foods.

They excluded the one randomised controlled trial from the US that directly linked ultraprocessed food consumption with weight gain and overeating because of its small size and short duration — it included just 20 participants and lasted one month.

That was a mistake, Nestle said. That study was tightly controlled and clearly showed that ultraprocessed foods caused people to overeat and gain weight, she said. It’s difficult and expensive to conduct larger and longer-term trials in nutrition, she added, so rather than wait for more evidence, she thinks the existing research is sufficient to recommend that people eat fewer ultraprocessed foods.

Dr Dariush Mozaffarian, cardiologist and director of the Food is Medicine Institute at Tufts University, US, agreed — adding that the evidence linking ultraprocessed foods to poor health is most consistent for those that are high in certain ingredients, like refined carbohydrates, added sugars and sodium.

If the next version of the dietary guidelines fails to include guidance on limiting ultraprocessed foods, it’s “a missed opportunity” to help steer Americans toward healthier diets, he added.

It’s challenging for health experts to make recommendations on ultraprocessed foods when the science is still emerging, said Maya Vadiveloo, an associate professor of nutrition at the University of Rhode Island, US.

The ultraprocessed food category is broad, and if you recommend avoiding all of them, you might be cutting out some foods that are actually beneficial, she added. Breakfast cereals and yogurts, for instance, have been associated with lower risks of cardiovascular disease and type 2 diabetes.

We need much more research to tease out these nuances, several experts agreed. But some said that it’s not too soon to start incorporating some of this guidance into federal recommendations.

NYTNS