A sprawling, decades-long study tracking more than 460,000 American adults is fundamentally challenging conventional wisdom regarding ultra-processed foods and their relationship to colorectal cancer. While ultra-processed foods have increasingly become the primary target of public health warnings due to their ubiquity in the modern diet and suspected links to chronic illnesses, new research suggests that painting the entire category with a single brush may be misleading.
The comprehensive research project discovered 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 crucial and nuanced distinction: the health outcomes associated with these foods varied dramatically depending on the specific type of food consumed. While certain categories of ultra-processed items were correlated with reduced cancer rates, others showed a clear association with elevated risks.
Led by Erikka Loftfield of the National Cancer Institute and published in the open-access journal PLOS Medicine, the findings strongly imply that the health effects of ultra-processed foods depend far more on their underlying nutritional composition than on the industrial processing methods used to manufacture them.
The Modern Diet Under the Microscope
Ultra-processed foods—broadly defined as industrial formulations made mostly or entirely from substances extracted from foods or synthesized in laboratories, often containing additives, colorings, and flavor enhancers—now account for more than half of all calories consumed by American adults. In recent years, these convenience-driven products have attracted intense scientific and public scrutiny because of their suspected connections to a wide range of chronic health conditions, including obesity, cardiovascular disease, and colorectal cancer.
Yet, the category itself is remarkably diverse. It encompasses an exceptionally wide assortment of items, ranging from artificially flavored sugary beverages and heavily processed convenience meals to mass-produced whole-grain breads, fortified breakfast cereals, and packaged dairy products. This vast heterogeneity has long made it difficult for nutritional epidemiologists to accurately judge the health effects of ultra-processed foods as a single, homogenous group.
For instance, previous observations have occasionally hinted that some ultra-processed whole-grain and dairy products might share different health trajectories than products like processed meats, which have long been linked by public health organizations to an increased risk of gastrointestinal malignancies. This inherent complexity raised an urgent scientific question: Is the level of industrial processing alone actually a reliable or useful indicator of a food’s ultimate health impact?
A Massive Study Tracks Cancer Risk for Nearly 19 Years
To rigorously investigate these differences and untangle the complicated relationship between processing levels and cancer incidence, researchers turned to one of the most comprehensive public health datasets available. They examined detailed health and dietary records from 461,682 American adults who were between the ages of 50 and 71 when they initially enrolled in the landmark NIH-AARP Diet and Health Study during 1995 and 1996.
At the very beginning of this monumental study, participants completed extensive, validated questionnaires detailing how frequently they consumed a wide array of different foods and beverages. Nutritional researchers and epidemiologists utilized these detailed responses to estimate each individual participant’s baseline intake of ultra-processed foods, categorizing and quantifying their dietary habits.
Following the initial baseline assessments, participants were tracked meticulously through 2018. The median follow-up period extended an impressive 18.8 years, providing researchers with a robust longitudinal window to examine how specific dietary patterns and consumption habits were associated with the development of colorectal cancer over nearly two decades of life.
When the research team first analyzed the broad data regarding total consumption, the results showed no overarching association between total ultra-processed food intake and colorectal cancer incidence. In simpler terms, participants who consumed a higher volume of ultra-processed foods did not, as an aggregated group, experience higher rates of colorectal cancer compared to those who ate fewer of these products. However, when the investigators peeled back the layers and looked closer at individual food categories rather than the broad, overarching umbrella of ultra-processed foods, a much more complicated and revealing picture emerged.
Some Ultra-Processed Foods Linked to Lower Cancer Risk
Rather than finding uniform harm across the board, the researchers discovered that higher consumption of specific subsets of ultra-processed foods—namely whole grains, dietary fiber, dairy products, and calcium derived from ultra-processed food sources—was actually associated with a lower incidence of colorectal cancer.
Conversely, meat products originating from ultra-processed sources demonstrated the exact opposite pattern, with greater consumption correlating directly with a higher incidence of cancer over the follow-up period.
The research team also sought to understand the potential clinical benefits of dietary substitution—specifically, what might happen if individuals replaced a portion of their ultra-processed food intake with less processed alternatives. Their sophisticated statistical analysis revealed that substituting minimally processed foods for just 10% of a person’s ultra-processed food intake by weight was associated with a 2% lower incidence of colorectal cancer.
These findings suggest that the specific nutritional characteristics and constituent ingredients of individual foods are far more informative than simply categorizing everything under the broad banner of being ultra-processed. Foods that are placed into the very same industrial processing category can harbor vastly different, and sometimes opposing, associations with human cancer risk.
Why the Findings Come With Important Limitations
Despite the sheer scale of the study, its massive participant pool, and its exceptionally lengthy follow-up period, the researchers are careful to emphasize that its conclusions come with notable caveats and may not apply universally to every demographic group.
Most prominently, the vast majority of participants enrolled in the NIH-AARP Diet and Health Study were older, white Americans. Because of this demographic skew, the findings may not accurately reflect the dietary habits, biological responses, or health experiences of younger adults or more racially and ethnically diverse populations living in the United States.
Another critical limitation inherent in the study’s design involves the collection of dietary information. Participants reported their eating habits and food frequencies only once at the very beginning of the study in the mid-1990s. Because of this single-point baseline assessment, researchers were fundamentally unable to account for changes, modifications, or evolutions in individual diets over the subsequent two decades.
Furthermore, the commercial availability, formulation, and sheer variety of ultra-processed foods expanded dramatically during the decades following the study’s launch. As a result of these sweeping shifts in the American food supply, 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 was observational in nature, it cannot definitively establish direct causality—meaning the study cannot prove whether particular foods directly increase or decrease cancer risk on a biological level, only that statistical associations exist.
What the Results Mean for a Healthy Diet
Rather than treating all ultra-processed foods as equally dangerous or equally benign, the findings strongly support evaluating foods primarily according to their underlying nutritional content and their specific, documented health associations.
The results also align remarkably well with existing, long-standing dietary recommendations for colorectal cancer prevention. Public health guidelines have consistently encouraged individuals to consume adequate amounts of whole grains, dietary fiber, dairy products, and calcium-rich foods, while simultaneously advising caution and limits on the consumption of processed meats.
Reflecting on the implications of the data, Erikka Loftfield noted 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, she emphasized that when individual food groups—such as whole grains, dairy, and meat—were evaluated by their ultra-processed or non-ultra-processed sources, the observed associations aligned cleanly with current dietary guidance for colorectal cancer prevention, showing that higher whole grain and dairy intake, alongside lower meat intake, correlated with lower colorectal cancer incidence.
Ultimately, the comprehensive study highlights why relying solely on the broad label of "ultra-processed" may fail to tell the whole story. When it comes to evaluating the complex risks of colorectal cancer, the specific types of foods people choose to eat appear to matter significantly more than their industrial processing classification alone.
The research was funded by the Intramural Research Program of the National Cancer Institute, part of the National Institutes of Health. Several authors are current or former employees of the National Cancer Institute’s Intramural Research Program, and the funding organization played no role in the design of the study, the collection or analysis of data, the decision to publish, or the preparation of the manuscript.