Americans love frozen meals and processed foods. We still don't fully understand what it's doing to our bodies.

Unprocessed or minimally processed foods typically include whole foods like fresh fruits, vegetables, eggs, fish, and nuts. Any time a whole food is significantly changed from its original state, at least some "processing" of that food has to occur. The processing can be chemical, in which added chemicals change the state of the food, or mechanical, whereby the food changes shape, texture, and appearance.

Experts at UCLA Health suggest that many minimally processed foods can be a nutritious part of our diets, including items like frozen fruits and vegetables or whole foods that have been canned. Foods fall into the "ultra-processed" category when they contain artificial flavors, colors, or additives that boost the saturated fat, sugar, and salt content well above that of the original ingredients.

Take the universally enjoyed chicken nugget, a processed food that has become a staple in children's diets. Chicken nuggets are made by deboning a chicken and grinding up the meat into a paste combined with chemicals, preservatives, and even food coloring before it's shaped into nuggets and deep-fried in oil. Other common ultra-processed foods include canned meats and deli meats, pizza, ice cream, canned soups, and potato chips.

Studies over the past decade have suggested that the evolution of American diets to include more processed foods may have expensive and deadly ramifications.

Unhealthy eating contributed to more deaths than smoking cigarettes—around 11 million globally each year, according to a comprehensive study of diets from 1990-2017 published in 2019. Other research has linked ultra-processed food consumption with the risk of premature death, diabetes, heart disease, and even dementia.

Researchers from the Tufts Institute for Global Obesity Research and other research institutions studying the dietary intake of young people suggested a link between ultra-processed diets and the rise of childhood obesity in a 2021 study. The National Heart, Lung, and Blood Institute reports that 1 in 5 children in the U.S. lives with obesity. The condition can put them at increased risk for other diseases like diabetes, cancer, heart disease, and breathing problems.

Diet-related obesity and other diseases can also contribute to poor mental health outcomes linked to their condition and due, at least in part, to stigmas surrounding obesity. The potential causes of obesity can be complex and include genetic predisposition, environmental factors, and dietary intake. Studies suggest between 20%-60% of people living with obesity experience mental health disorders, including depression and anxiety, a higher percentage than the overall population.

Diets are contributing to higher health care costs in the U.S. Diet-related diseases like heart disease and diabetes cost Americans $50 billion a year in health costs, according to 2019 research from the National Institutes of Health. That cost burden is shouldered not only by taxpayers but also by patients themselves.

Despite the connections scientists and researchers make between processed foods and poor health outcomes, experts still find evidence that we don't fully understand the implications.

Some ultra-processed foods have been found to have stronger associations with Type 2 diabetes than others, though the study by nutritionists at Harvard and elsewhere didn't identify why. In 2023, a panel of U.S. researchers convened to create a roadmap for future research that would illuminate how ultra-processed foods influence our metabolism—or the ability to break down and digest the resources in the food we eat. They also identified the need for more research on which processing or artificially formulated ingredients are the key drivers of obesity and other related diseases.

Federal agencies are likely to consider updating dietary guidelines to warn against eating ultra-processed foods. That change, if enacted, would come in 2025, according to The Washington Post.

However, the lack of concrete knowledge about how these foods affect our health and how to categorize them has also made it difficult for experts to agree on dietary recommendations for consuming processed foods.

The NOVA system has emerged as an imperfect, albeit commonly used resource for categorizing and identifying ultra-processed foods. However experts don't recommend using it to cut out all processed foods. Instead, they suggest adjusting diets within reason, making an effort to consume minimally or unprocessed foods alongside the ultra-processed ones often sought out for their affordability and comfort.

In an essay calling for more research and stricter regulation to protect Americans from the harms of ultra-processed foods, Jerold Mande, an adjunct Harvard professor and a former senior adviser to the Food and Drug Administration pointed out a 2019 study suggesting that factors other than carbohydrate, sodium, fat and sugar content may impact the associated weight gain.

"Our food must continue to be delicious, affordable, and convenient—traits Americans appropriately demand—but can be eaten daily without making us sick," he wrote.

Story editing by Alizah Salario. Additional editing by Kelly Glass. Copy editing by Kristen Wegrzyn. Photo selection by Lacy Kerrick.