The Dietary Guidelines Advisory Committee has been busy drafting recommendations for the 2025-2030 Dietary Guidelines for Americans, an exercise undertaken every five years. But as past advisory committees have found, a lack of relevant research has been a stumbling block.
The guidelines, which must be ratified and approved jointly by the Secretary of Agriculture and the Secretary of Health and Human Services, are intended to help combat diet-related diseases, inform federal feeding programs like school meals, and shape U.S. food policy.
At their fifth meeting last month, members of the committee frequently cited a lack of sufficient evidence in several key subjects.
Some in nutrition research argue the uncertainty is caused by a lack of federal focus and funding on nutrition and warn that it could hinder the committee’s ability to address key issues – especially that of ultra-processed food – that may affect Americans' health.
The previous guidelines did not address ultra-processed foods, but the current committee has shown a commitment to explore links between such products and diet-related diseases.
At its May meeting, the committee concluded that limited evidence suggests that diets with more ultra-processed foods consumed by children, adolescents, adults and older adults all are linked with greater fat mass, body mass index and the risk of being overweight.
The committee could not agree on a conclusory statement on the association between ultra-processed food and weight change for infants and children up to 24 months or during pregnancy and postpartum. The committee cited an inadequate body of evidence for both categories.
For example, the committee could cite only one article on ultra-processed foods consumed during postpartum and body composition.
“The issue of underinvestment in nutrition research is an enormous one,” said Marion Nestle, emeritus professor of nutrition, food studies and public health at New York University.
Specifically on ultra-processed foods, more than 1,500 published studies rely primarily on observational data where participants self-report eating habits, she said. These can be slightly less reliable since participants could misremember or falsely report what they eat.
The committee ultimately included 16 studies on ultra-processed foods consumed by adults.
National Institutes of Health funding on nutrition research is primarily directed toward precision nutrition, which examines specific genetic issues that make individuals require more or less of certain nutrients, Nestle said. This individualized approach has fewer public health implications.
However, it is more challenging to conduct studies on nutrition that can both meet the standard of evidence required for the DGA committee and have broad public health applications. This is in part because of limited capacity, and the potentially stringent demands on participants.
As a result, little funding is dedicated to researching some of the most prevalent nutrition problems in the U.S. like obesity or diet-related chronic diseases, Nestle said.
Still, the broader conclusion from the available studies is that people who eat ultra-processed foods are less healthy than people who don’t, Nestle said.
“The philosophical issues involved in this are really very important and they have to do with how much evidence do you need before you make public health recommendations,” Nestle said. “I think we have enough on ultra-processed foods, but other reasonable people can disagree.”
Nutrition experts point to a 2019 study by Kevin Hall, senior investigator at the National Institutes of Health, said to be the first randomized controlled trial to evaluate ultra-processed versus less-processed diets.
What was unique, and important, about his research is Hall's recruitment of participants to stay at an NIH facility for a four-week period, where they were randomly assigned an ultra-processed or less-processed diet for two weeks at a time before switching diets.
The study structure gave Hall greater control and reliability over the participants' diets, unlike observational studies that rely on voluntary information.
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Participants gained weight and consumed more calories on the ultra-processed diet. On the less-processed diet, participants lost weight and consumed fewer calories.
While this is one of the few studies available that offers a controlled study of ultra-processed foods, Nestle noted the committee was instructed to dismiss it because of its short time frame.
Nutrition research in general is difficult to execute well because of difficulties in setting a controlled environment. Most research facilities don’t have space to house people similar to Hall’s study.
Over the years, DGAC has been required to produce evidence-based recommendations, rather than looking at all the available evidence, Nestle said. This standard will hinder its ability to act on things like ultra-processed foods, because the “evidence isn’t there and will never be there,” she said.
The next DGAC meeting will be Sept. 26, with the final report expected later this fall. While it’s still to be determined what the committee will include in its final report, Nestle said it’s unlikely it will include substantive recommendations on ultra-processed foods because of the limitations.
“What’s essential is that these dietary guidelines recognize that there are ultra-processed foods and that the evidence is overwhelming that these foods are making us sick,” said Jerold Mande, an adjunct professor of nutrition at Harvard’s School of Public Health.
The committee considered abundant evidence in traditional areas of concern such as saturated fats, added sugar and sodium among different population groups. This demonstrates that such research can be done but is a matter of focus and funding, said a former USDA official.
Historically, the DGA and federal feeding programs like school meals have been framed around the content of fat, salt and sugar (HFSS) where nutrients are addressed. This framework allows ultra-processed foods in school meals because of the lack of dietary guidance, the official said.
During the most recent meeting, some members of the committee expressed concern about strongly urging against ultra-processed foods without an economic alternative and that focusing guidelines on processing could distract consumers from understanding nutritional content.
Overall, there appeared to be consensus in the committee that more research is necessary.
“We look at the science around questions for which there is great federal interest and for which there is great stakeholder interest,” said Cheryl Anderson, member of a subcommittee for dietary patterns and specific dietary pattern components across life stages. She said, “We’ve come to the conclusion that we’ve come to because it’s a novel topic area and the science isn’t ripe yet.”
The committee recommended a number of additional research topics to provide clarity on the degree of processing that makes a food ultra-processed, and that better defines the term.
“We're great at waiting until the house is on fire and then responding, but in this case, it's resulted in the level of illness in our population, shorter lifespans, sick children,” Mande said. “And I think our house is on fire. It's time to act.”
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