A massive, nearly two-decade-long study tracking more than 460,000 American adults is challenging prevailing assumptions about ultra-processed foods and their relationship to colorectal cancer. While ultra-processed foods (UPFs) have increasingly become the target of public health warnings due to their ubiquity in modern diets and broad connections to various chronic health issues, new research suggests that evaluating them simply as a single, uniform category may miss the bigger picture.
The comprehensive research, led by Erikka Loftfield of the National Cancer Institute and published October 15 in the open-access journal PLOS Medicine, found that eating higher overall quantities of ultra-processed foods was not directly associated with a higher overall incidence of colorectal cancer. However, a deeper, more granular dive into the data revealed a much more nuanced reality: the health effects of these foods depend heavily on what those products actually contain. While certain categories of ultra-processed items were linked to a lower risk of developing the disease, others were clearly associated with elevated cancer rates.
Ultra-processed foods currently account for more than half of all calories consumed by American adults. These commercially manufactured items—which typically undergo extensive industrial processing and often include added substances such as flavors, colors, sweeteners, or emulsifiers—have attracted intense scientific and public scrutiny in recent years. Researchers have increasingly sought to understand their potential connections to chronic illnesses, including colorectal cancer, which remains one of the most commonly diagnosed and lethal cancers in the United States.
Yet, the category itself is remarkably diverse. It encompasses an expansive range of items, stretching from nutrient-dense whole-grain breads and fortified dairy beverages to sugary soft drinks, salty snacks, and heavily processed meats. Because the umbrella term covers such a vast array of chemical compositions and nutritional profiles, public health experts have increasingly debated whether the broad level of industrial processing alone is a sufficiently useful indicator of a food’s potential health consequences.
The new findings suggest it may not be. When researchers looked closer at specific food subgroups within the broader UPF classification, striking divergences emerged. For instance, certain ultra-processed whole-grain products and dairy items were actually associated with a lower risk of colorectal cancer. Conversely, processed meats within the ultra-processed category were consistently linked to a higher risk. These contrasting outcomes raise fundamental questions about whether the nutritional composition of an individual food item dictates its health impact far more than the factory methods used to manufacture it.
A Massive Study Tracks Cancer Risk for Nearly 19 Years
To investigate these complex dietary distinctions and trace potential long-term health outcomes, researchers examined extensive health and dietary records from 461,682 American adults. The participants were between the ages of 50 and 71 when they initially enrolled in the landmark NIH-AARP Diet and Health Study between 1995 and 1996.
At the very beginning of the study period, participants completed detailed questionnaires describing how frequently and in what amounts they consumed a wide variety of different foods. Using these self-reported dietary responses, researchers calculated and estimated each individual’s baseline intake of ultra-processed foods, categorizing the foods based on the extent and purpose of industrial processing they underwent.
The participant cohort was then tracked through 2018, yielding a median follow-up period of 18.8 years. This exceptionally long observation window provided the research team with a rare opportunity to examine how varying long-term dietary patterns were associated with the actual development of colorectal cancer over a span of nearly two decades.
When the initial data was analyzed as a whole, the results showed no overall statistical association between total ultra-processed food consumption and colorectal cancer incidence. In practical terms, participants who consumed a higher volume of ultra-processed foods did not, as a collective group, experience higher rates of colorectal cancer compared to those who ate fewer of these items.
However, because broad categorizations can mask underlying patterns, the research team pushed past the aggregate numbers to examine individual food categories, revealing a significantly more complicated picture of how diet intersects with cancer risk.
Some Ultra-Processed Foods Linked to Lower Cancer Risk
By breaking down the data into specific food groups, the researchers found that higher consumption of whole grains, dietary fiber, dairy products, and calcium—even when sourced from ultra-processed foods—was consistently associated with a lower incidence of colorectal cancer. This unexpected nuance challenges the notion that all items emerging from industrial processing plants carry the exact same metabolic and oncological risks.
Meat products derived from ultra-processed sources, however, showed the exact opposite pattern. Greater consumption of ultra-processed meats was clearly associated with a higher incidence of colorectal cancer among the study population, aligning with decades of prior epidemiological research regarding processed meats.
To further understand the public health implications of these dietary patterns, the team also modeled what might happen if individuals replaced ultra-processed foods with less processed alternatives. Their substitution analysis calculated that replacing minimally processed foods for just 10% of a person’s daily ultra-processed food intake by weight was associated with a modest but statistically significant 2% lower incidence of colorectal cancer.
These findings strongly suggest that the fundamental nutritional characteristics of individual foods provide far more informative guidance than simply labeling everything under the sweeping umbrella of "ultra-processed." Foods placed side-by-side in the same broad industrial processing category can have vastly different, and sometimes diametrically opposed, associations with long-term cancer risk.
Why the Findings Come With Important Limitations
Despite the undeniable strengths of the study—including its massive sample size, prospective design, and exceptionally lengthy follow-up period—the researchers are careful to emphasize that its conclusions come with notable limitations and may not apply equally across all segments of the population.
First, the demographic composition of the study cohort skews heavily. The vast majority of participants in the NIH-AARP Diet and Health Study were older, white Americans. Consequently, the findings may not accurately reflect the dietary habits, health risks, or physiological responses of younger adults, or of more racially and ethnically diverse populations whose dietary cultures and baseline health statuses might differ substantially.
Another important limitation centers on how dietary information was collected. Participants reported their eating habits through questionnaires only once, right at the very beginning of the study in the mid-1990s. Because of this single baseline assessment, researchers were unable to account for any subsequent changes, improvements, or deteriorations in individual diets over the nearly two decades of follow-up.
Furthermore, the commercial marketplace underwent a massive transformation during and after the study’s inception. The availability, marketing, and sheer variety of ultra-processed foods expanded dramatically in the late 20th and early 21st centuries. As a result, the initial dietary assessments may have underestimated participants’ actual cumulative consumption of ultra-processed foods during the later years of the tracking period.
Finally, because the research is observational in nature, it cannot definitively establish direct causality. Observational studies can identify statistical correlations and patterns, but they cannot prove whether particular foods directly cause or prevent cancer on a biological level, as other unmeasured lifestyle factors could potentially influence the results.
What the Results Mean for a Healthy Diet
Rather than treating all ultra-processed foods as an equally harmful monolith, the new findings support a more nuanced approach to public nutrition. Experts suggest that foods should be evaluated according to their specific nutritional content and individual health associations rather than a blanket processing label.
Crucially, the results align closely with existing, long-standing dietary recommendations for colorectal cancer prevention. Current public health guidelines consistently encourage individuals to consume adequate amounts of whole grains, dietary fiber, dairy products, and calcium-rich foods while actively limiting the intake of processed meats.
Dr. Erikka Loftfield summarized the core takeaway of the research, explaining that within this large population of older US adults, researchers did not observe a direct association between total ultra-processed food intake and colorectal cancer incidence. However, when the team analyzed specific food groups—such as whole grains, dairy, and meat—by their UPF or non-UPF source, the resulting associations fell squarely in line with current dietary guidance for colorectal cancer prevention. Specifically, higher intakes of whole grains and dairy, coupled with lower intakes of meat, were consistently associated with lower colorectal cancer incidence, regardless of the industrial processing label.
Ultimately, the study highlights why the broad label "ultra-processed" may ultimately fail to tell the whole story. When it comes to the complex relationship between diet and colorectal cancer, the actual nutritional components and specific kinds of foods people choose to eat appear to matter far more than their broad industrial processing category alone.
The study was funded entirely by the Intramural Research Program of the National Cancer Institute, part of the National Institutes of Health. Several authors of the published paper are current or former employees of the National Cancer Institute’s Intramural Research Program, though the funding organization played no role in designing the study, collecting or analyzing the data, deciding whether to publish the findings, or preparing the final manuscript.
