A massive, nearly two-decade study involving more than 460,000 American adults is challenging prevailing assumptions regarding ultra-processed foods and their relationship to colorectal cancer. While public health messaging has increasingly cast a wide net of suspicion over heavily processed items, researchers found that eating a higher total amount of ultra-processed food was not actually associated with a higher overall incidence of colorectal cancer. However, a deeper dive into the data revealed a much more nuanced and critical distinction: the health implications depend heavily on what those specific foods actually contain, with certain categories linked to lower cancer rates and others tied to elevated risks.
The research, led by Erikka Loftfield of the National Cancer Institute and published in the open-access journal PLOS Medicine, suggests that simply categorizing a food by its level of processing may overlook vital nutritional details. As ultra-processed items continue to account for more than half of all calories consumed by American adults, these products have faced mounting scrutiny over potential connections to chronic diseases, including colorectal cancer. Yet, the category itself encompasses an extraordinarily diverse assortment of grocery items—ranging from nutrient-dense whole-grain breads to processed meats and sugary confections—making it remarkably difficult to evaluate their health effects accurately as a single, monolithic group.
For instance, prior dietary patterns and specific sub-analyses indicate that certain ultra-processed whole grain and dairy products have historically associated with a lower risk of colorectal cancer, whereas processed meats have consistently mapped to a higher risk. This dichotomy raises a fundamental question for nutritional scientists and public health advocates alike: whether the mere level of industrial processing is truly a useful standalone indicator of a food’s potential long-term health effects, or if the underlying nutritional profile remains the paramount factor.
A Massive Study Tracks Cancer Risk for Nearly 19 Years
To investigate these complex dietary differences and clarify the relationship between industrial processing and gastrointestinal health, researchers turned to one of the most comprehensive public health databases available. They examined detailed health and dietary records from 461,682 American participants 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 the study, participants completed extensive, self-administered questionnaires detailing how frequently they consumed a wide variety of different foods over the previous year. Researchers utilized these detailed dietary responses to carefully estimate each individual’s overall daily intake of ultra-processed foods, applying standard food classification systems to sort items based on the degree and nature of industrial processing they underwent prior to purchase.
Following the baseline dietary assessments, the participants were tracked meticulously through 2018. This robust tracking period resulted in a median follow-up duration of 18.8 years, offering researchers a remarkably expansive window to examine how real-world dietary patterns over nearly two decades associated with the eventual development of colorectal cancer.
When the statistical analyses were finally complete, the initial results surprised many who expected a direct correlation. The data showed no overall association between total ultra-processed food consumption and colorectal cancer incidence. In other words, participants who consumed higher quantities of ultra-processed foods did not, as a collective group, experience higher rates of colorectal cancer compared to those who consumed lesser amounts. However, when the research team peeled back the layers to examine individual food categories within the broader processing spectrum, a much more complicated and revealing picture emerged.
Some Ultra-Processed Foods Linked to Lower Cancer Risk
Rather than condemning the entire category of ultra-processed foods, a granular look at the data demonstrated that the specific nutritional components of the foods mattered far more than the manufacturing processes used to make them. The researchers found that higher consumption of whole grains, dietary fiber, dairy products, and calcium—even when sourced from foods classified as ultra-processed—was significantly associated with a lower incidence of colorectal cancer.
Conversely, meat products derived from ultra-processed sources showed the exact opposite pattern, with greater consumption clearly associated with a higher cancer incidence. This stark divergence within the same broad classification category underscores why blanket warnings can sometimes obscure vital dietary truths.
To further test these associations, the research team also examined theoretical scenarios involving dietary substitution, analyzing what might happen if individuals replaced ultra-processed foods with less processed alternatives. Their simulation models found that substituting minimally processed foods for just 10% of a person’s total ultra-processed food intake by weight was associated with a modest yet statistically significant 2% lower incidence of colorectal cancer.
These collective findings strongly suggest that the fundamental nutritional characteristics of individual foods provide far more reliable guidance than simply grouping everything under the umbrella term of "ultra-processed." Foods placed in the exact same broad industrial category can carry vastly different, and sometimes opposing, associations with long-term cancer risk.
Why the Findings Come With Important Limitations
Despite the sheer scale of the study, its exceptional statistical power, and the lengthy follow-up period spanning nearly two decades, the researchers have been careful to emphasize important caveats, noting that their conclusions may not apply universally to every demographic group.
A primary limitation stems from the demographic makeup of the cohort itself. The vast majority of participants in the NIH-AARP Diet and Health Study were older, white Americans. Consequently, these findings may not accurately reflect the dietary realities, biological responses, or cancer risks experienced by younger adults, or by individuals from more racially and ethnically diverse populations whose dietary habits, access to healthcare, and genetic backgrounds may differ significantly.
Another crucial limitation involves the methodology surrounding data collection. Participants reported their eating habits through questionnaires only once, at the very beginning of the study in the mid-1990s. Because of this single baseline measurement, researchers could not account for how individual diets naturally evolved, improved, or deteriorated over the subsequent decades of follow-up.
Furthermore, the commercial availability, formulation, and sheer variety of ultra-processed foods in the American food supply expanded dramatically during the decades following the baseline survey. As a result, the initial dietary assessments may have inadvertently underestimated participants’ actual cumulative consumption of ultra-processed foods as the food landscape transformed around them.
Finally, because the research was fundamentally observational in design, it cannot definitively establish direct cause and effect—meaning the study cannot prove whether particular foods directly increase or decrease cancer risk on an individual biological level, only that certain dietary patterns are statistically associated with different cancer rates.
What the Results Mean for a Healthy Diet
Rather than treating all ultra-processed foods as equally harmful or universally toxic, the findings strongly support evaluating foods based on their distinct nutritional content and specific, documented health associations. The results align remarkably well with existing, established dietary recommendations for colorectal cancer prevention, which consistently encourage the public to consume adequate amounts of whole grains, dietary fiber, dairy products, and calcium-rich foods while actively limiting the intake of processed meats.
Reflecting on the implications of the research, lead investigator 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 examining individual food groups—such as whole grains, dairy, and meat—by their processing source revealed that the underlying associations remained entirely consistent with current dietary guidance for preventing colorectal cancer, reinforcing that higher whole grain and dairy intake, alongside lower meat intake, correlates with lower cancer incidence.
Ultimately, this comprehensive study highlights why the broad label "ultra-processed" may ultimately fail to tell the whole story. When it comes to complex health outcomes like colorectal cancer, the specific kinds of foods people choose to eat appear to matter far more than the industrial processing category to which those foods belong.
The study was funded entirely 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 designing the study, collecting or analyzing the data, deciding to publish the findings, or preparing the final manuscript.