A sweeping new nutritional study tracking more than 460,000 American adults over nearly two decades is challenging long-held assumptions regarding ultra-processed foods and their relationship to colorectal cancer. Contrary to the prevailing narrative that treats all ultra-processed items as a uniform health threat, researchers discovered that eating a high volume of ultra-processed food as a broad category was not directly associated with a higher overall incidence of colorectal cancer.
However, the findings revealed a much more nuanced and critical distinction: the health implications depend heavily on what those specific foods actually contain. While certain categories of ultra-processed foods were surprisingly linked to lower rates of cancer, others were clearly associated with an increased risk.
The research, spearheaded by Erikka Loftfield of the National Cancer Institute and published in the open-access journal PLOS Medicine, suggests that evaluating foods solely by their level of industrial processing may overlook vital nutritional factors. Ultra-processed foods currently account for more than half of all calories consumed by adults in the United States. In recent years, these convenient, ready-to-eat products have attracted intense public scrutiny and regulatory concern because of their potential connections to a wide range of chronic diseases, including colorectal cancer. Yet, the category itself is remarkably diverse, encompassing everything from heavily processed industrial snacks to fortified whole-grain breads and nutrient-dense dairy products. This vast heterogeneity has long made it difficult for nutritional epidemiologists to accurately judge the health effects of the category as a single group.
For example, prior nutritional observations have noted that certain ultra-processed whole-grain and dairy products are frequently associated with a reduced risk of colorectal cancer, whereas processed meats—often falling into the same broad processing classification—have consistently been linked to a heightened risk. This paradox raises a fundamental question for modern public health experts: Is the industrial level of processing alone a truly useful indicator of a food’s potential health effects, or are the underlying nutritional components far more important?
A Massive Study Tracks Cancer Risk for Nearly 19 Years
To investigate these complex nutritional differences and untangle the relationship between manufacturing processes and cancer outcomes, researchers embarked on an extensive examination of health and dietary records. The study utilized data 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 the study period, participating individuals completed comprehensive questionnaires detailing how frequently they consumed a wide array of different foods and beverages. Nutritional researchers and epidemiologists used these detailed self-reported responses to estimate each individual participant’s baseline intake of ultra-processed foods, categorizing them according to established international food processing frameworks.
Following the initial dietary assessments, the participants were tracked meticulously through 2018. The study achieved a remarkable median follow-up period of 18.8 years, allowing the research team to observe how long-term dietary patterns were associated with the actual clinical development of colorectal cancer over nearly two decades of adult life.
When the researchers initially analyzed the aggregate data, the results showed no overall statistical association between total ultra-processed food consumption and colorectal cancer incidence. In simpler terms, participants who consumed a higher proportion of ultra-processed foods did not, as a unified group, experience elevated rates of colorectal cancer compared to those who ate fewer of these products. However, when the research team dug deeper and examined individual food categories rather than the broad umbrella term, a much more complicated and revealing picture began to emerge.
Some Ultra-Processed Foods Linked to Lower Cancer Risk
Breaking down the dietary data by specific food groups yielded starkly contrasting outcomes. The investigators found that higher consumption of whole grains, dietary fiber, dairy products, and calcium—even when sourced from foods classified as ultra-processed—was consistently associated with a lower incidence of colorectal cancer.
Conversely, meat products derived from ultra-processed sources showed the exact opposite pattern. Greater consumption of ultra-processed meats was clearly associated with a higher cancer incidence, reinforcing established concerns regarding meat preservation and processing techniques.
To further evaluate the clinical relevance of these choices, the research team also modeled what might happen if consumers actively replaced ultra-processed foods with less processed nutritional 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 over the study period.
These compelling findings strongly suggest that the intrinsic nutritional characteristics of individual foods provide far more reliable information than simply stamping every item with a broad "ultra-processed" label. Foods placed side-by-side within the same industrial processing category can have drastically different, and sometimes opposing, biological associations with long-term cancer risk.
Why the Findings Come With Important Limitations
Despite the extraordinary scale of the study, its exceptionally large participant pool, and its nearly two-decade follow-up duration, the authors are careful to emphasize that its conclusions come with notable limitations and may not apply universally to every demographic group.
One primary consideration involves the demographic makeup of the cohort. The vast majority of participants in the NIH-AARP Diet and Health Study were older, white adults living in the United States. Consequently, the findings may not accurately reflect the dietary habits, biological responses, or disease risks of younger adults or more racially and ethnically diverse populations.
Another significant methodological constraint involves the collection of dietary information. Participants reported their specific eating habits and food frequencies only once, right at the beginning of the study in the mid-1990s. Because subsequent dietary tracking was limited, the researchers could not account for how individual diets naturally evolved, improved, or deteriorated over the ensuing decades of adult life.
Furthermore, the commercial availability, formulation, and overall variety of ultra-processed foods expanded dramatically in the United States during the decades following the initial survey. As a direct result of this food environment evolution, the baseline dietary assessments may have inadvertently underestimated participants’ actual cumulative consumption of ultra-processed products during the full length of the study period.
Finally, because the research was fundamentally observational in nature, it cannot definitively establish direct cause-and-effect relationships. Observational studies can identify correlations and associations within large populations, but they cannot prove definitively whether particular foods directly increase or decrease an individual’s personal cancer risk.
What the Results Mean for a Healthy Diet
Rather than treating all ultra-processed foods as equally harmful or uniformly toxic, the new findings support a more discerning approach to nutrition—evaluating foods primarily according to their nutrient profile and specific, documented health associations rather than their manufacturing pedigree.
The results also align closely with existing, well-established public health dietary recommendations for colorectal cancer prevention. These current clinical 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 research, lead investigator Erikka Loftfield noted that within this large population of older US adults, researchers observed no overall link between total ultra-processed food intake and colorectal cancer incidence. However, when looking closely at specific food groups—such as whole grains, dairy, and meat—by their processed or non-processed source, the associations aligned neatly with current dietary guidance for cancer prevention. Specifically, higher intakes of whole grains and dairy, coupled with lower intakes of meat, were consistently associated with lower colorectal cancer incidence.
Ultimately, this extensive study highlights why the broad and often-feared label "ultra-processed" may not tell the whole nutritional story. When it comes to understanding and preventing colorectal cancer, the specific kinds of foods people choose to eat appear to matter far more than their industrial processing category 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. 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.