A massive, nearly two-decade-long study involving more than 460,000 American adults is challenging long-held assumptions regarding ultra-processed foods and their connection to colorectal cancer. While public health messaging has increasingly cast ultra-processed foods (UPFs) as a uniform dietary villain linked to a broad array of chronic illnesses, new research suggests the reality is significantly more complex.
Researchers leading the expansive investigation found that eating a higher quantity of ultra-processed foods overall was not associated with a higher overall incidence of colorectal cancer. However, when looking beneath the surface of broad categorization, the findings revealed a critical distinction: certain types of ultra-processed foods were actually linked to lower cancer rates, while others were firmly associated with higher rates.
Published on October 15 in the open-access journal PLOS Medicine and spearheaded by Erikka Loftfield of the National Cancer Institute, the research suggests that the health impacts of ultra-processed foods may depend far less on the industrial processing level itself and far more on the actual nutritional composition of the individual foods.
In modern Western diets, ultra-processed foods account for more than half of all calories consumed by American adults. These convenient, highly marketable, and often inexpensive products have attracted intense scientific and public scrutiny in recent years because of their potential connections to a wide range of chronic health conditions, including obesity, cardiovascular disease, and colorectal cancer. Yet the category itself is remarkably diverse, encompassing everything from artificially flavored sugary sodas and packaged pastries to fortified whole-grain breads and nutrient-dense dairy items. This vast diversity has long made it difficult for nutritional epidemiologists to accurately judge the health effects of the category as a single, homogenous group.
The nuances hidden within these classifications become clearer when examining specific food groups. Prior observations and current analyses indicate that some ultra-processed whole-grain products and dairy items are associated with a reduced risk of colorectal cancer, whereas processed meats—regardless of how they are packaged or processed—have consistently been linked to an elevated risk. This stark contrast raises fundamental questions about whether the degree of processing alone serves as a reliable or useful indicator of a food’s potential health consequences.
A Massive Study Tracks Cancer Risk for Nearly 19 Years
To investigate these complex dietary differences and clarify the relationship between processing levels and cancer incidence, researchers examined comprehensive 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 during 1995 and 1996.
At the very beginning of the study, participants completed detailed questionnaires describing how frequently they consumed a wide variety of different foods and beverages. Researchers used these extensive dietary responses to calculate and estimate each individual participant’s intake of ultra-processed foods, classifying items according to standard nutritional frameworks.
Following the initial baseline assessments, participants were tracked meticulously through 2018. The resulting median follow-up period spanned an impressive 18.8 years, providing investigators with a robust dataset that allowed them to examine how distinct dietary patterns were associated with the development of colorectal cancer over nearly two decades of life.
The initial results of this long-term tracking showed no overall statistical association between total ultra-processed food consumption and colorectal cancer incidence. In simpler 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, when the research team peeled back the layers to perform a closer examination of individual food categories rather than the broad UPF label, a much more complicated and informative picture emerged.
Some Ultra-Processed Foods Linked to Lower Cancer Risk
Rather than painting all ultra-processed foods with the same broad brush, the researchers discovered that higher consumption of specific sub-categories—namely whole grains, dietary fiber, dairy products, and calcium derived from ultra-processed food sources—was associated with a lower incidence of colorectal cancer.
Meat products originating from ultra-processed sources showed the exact opposite pattern. Greater consumption of ultra-processed meats was clearly associated with a higher cancer incidence over the course of the study period.
To further test the practical implications of these dietary patterns, the research team also examined what might happen theoretically if ultra-processed foods were systematically replaced with less processed alternatives. Their substitution analysis found that replacing minimally processed foods for just 10% of a person’s ultra-processed food intake by weight was associated with a modest yet statistically significant 2% lower incidence of colorectal cancer.
These findings strongly suggest that the fundamental nutritional characteristics of individual foods carry far more weight and provide much more predictive value than simply classifying everything by its processing level. Foods placed within the same broad, catch-all processing category can have wildly different, and sometimes opposing, associations with long-term cancer risk.
Why the Findings Come With Important Limitations
Despite the undeniable strengths of the study, which include its massive sample size, prospective design, and exceptionally lengthy follow-up period, the researchers emphasize that its conclusions come with notable limitations and may not apply universally to every demographic group.
Most notably, 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, health risks, or life experiences of younger adults or individuals from more racially and ethnically diverse populations.
Another important limitation involves the methodology used for collecting 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 unable to account for changes, improvements, or deteriorations in individual diets over the subsequent two decades.
Furthermore, the commercial availability, formulation, and overall variety of ultra-processed foods expanded dramatically during the decades following the initial survey. As a result, the baseline dietary assessments may have underestimated participants’ actual cumulative consumption of ultra-processed foods during the full duration of the study period.
Finally, because the research was observational in nature, it cannot definitively establish direct cause and effect—meaning it cannot prove whether particular foods directly increase or decrease an individual’s cancer risk on a biological level, but rather highlights strong statistical associations within a large population.
What the Results Mean for a Healthy Diet
Rather than treating all ultra-processed foods as equally harmful or beneficial, the findings strongly support evaluating foods primarily according to their underlying nutritional content and their specific, documented health associations.
The results also align neatly with existing, well-established public health dietary recommendations for colorectal cancer prevention. These 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.
Reflecting on the broader implications of the work, lead researcher Erikka Loftfield explained 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 noted that breaking down food groups like whole grains, dairy, and meat by their processing source revealed associations that align closely with current dietary guidance for colorectal cancer prevention, such that higher whole grain and dairy intakes, alongside lower meat intakes, correspond with lower cancer incidence.
Ultimately, the comprehensive study highlights why the broad label "ultra-processed" may fail to tell the whole story when it comes to human health. When evaluating the risk of colorectal cancer, the specific kinds and nutritional profiles of the foods people put on their plates appear to matter far more than their industrial processing category alone.
The study received funding support from 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, though 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.