Rising Incidence of Colorectal Cancer in Young Adults
The incidence of colorectal cancer has been steadily increasing among younger populations over recent years. While the underlying causes of this trend remain unclear, various studies suggest that dietary habits may play a significant role, particularly in relation to diets high in ultra-processed foods. A recent investigation has concluded that the impact of these foods varies based on their specific ingredients.
Led by researchers from the National Cancer Institute (NCI) in the United States, the study aimed to clarify the discrepancies found in earlier research. Some studies associate a high consumption of ultra-processed foods with an increased incidence of colorectal cancer, which encompasses both colon and rectal cancer, while others almost entirely dismiss this connection.
The findings were published this month in the journal PLOS Medicine, where the authors propose that the wide variety of products and formulations classified as ultra-processed foods may partly explain these conflicting conclusions.
Long-Term Study of Dietary Habits
To test their hypothesis, the researchers analysed data from over 460,000 participants involved in the NIH-AARP Diet and Health Study, a long-term follow-up investigation that commenced in 1995-1996 with American adults aged between 50 and 71 years.
Over an average span of 18.8 years, participants reported their dietary habits using a frequency questionnaire that included 124 foods and beverages, alongside inquiries about portion sizes, low-fat or high-fibre products, and cooking methods. The analysis revealed that ultra-processed foods constituted approximately 43% of the daily diet of participants, with over 10,000 new cases of colorectal cancer identified by 2018.
This comprehensive approach allowed researchers to compare the consumption of ultra-processed foods with specific food items and nutrients in relation to the cancer cases detected during the follow-up period. Consequently, the team could examine whether associations varied according to the type of product consumed, revealing patterns that broader analyses might overlook.
Exploring the Complex Relationship
Despite the depth of their investigation, the study did not find a conclusive relationship between overall consumption of ultra-processed foods and the incidence of colorectal cancer. However, the associations did vary when the research team analysed different types of products and their nutritional contributions separately.
Participants with the highest intake of processed meat and seafood experienced a 10% higher incidence of colorectal cancer compared to those who consumed less of these items. Conversely, among those who consumed more ultra-processed bread, cereals, and dairy products, the incidence of cancer decreased by approximately 9%, 16%, and 18%, respectively, compared to individuals who did not typically include these foods in their diets.
The authors caution that these findings do not definitively prove that consuming ultra-processed bread, cereals, or dairy prevents colorectal cancer. Similarly, they do not establish that processed meats are solely responsible for causing these tumours in all cases. The study was observational and merely identified differences that, in the researchers’ view, could be linked to the nutrients present in these specific product categories.
Nutritional Insights from Ultra-Processed Foods
To further understand these discrepancies, the researchers examined nutrients and food groups based on their origins, utilising the NOVA classification system, which categorises foods according to their level of processing.
In this analysis, the study indicated that each additional 300 milligrams of calcium consumed daily from ultra-processed foods was associated with a 23% lower incidence of cancer. When calcium was sourced from less processed food categories, the association still pointed towards a reduced incidence, albeit around 10%.
Conversely, each additional daily serving of meat from ultra-processed sources correlated with an 8% increase in colorectal cancer incidence, while an extra serving of meat from other categories was linked to a 4% rise.
Erikka Loftfield, a former NCI researcher and principal author of the study, highlighted, “We did not observe an association between the total intake of ultra-processed foods and the incidence of colorectal cancer. However, when we analysed food groups such as whole grains, dairy, and meat based on their origins, we found the associations aligned with current dietary recommendations for colorectal cancer prevention.”
Implications for Future Research
The authors emphasise that these figures describe statistical associations and do not indicate that obtaining calcium or consuming dairy through ultra-processed products is necessarily healthier than consuming less processed foods. They also acknowledge that the strong preference for processed foods among the American population limited the analysis of nutrients in other food categories.
Nonetheless, the study demonstrates that ultra-processed foods do not represent a uniform nutritional category; while some contribute components associated with a lower incidence of disease, others contain ingredients linked to a higher incidence. Thus, classifying them solely by their level of processing may obscure significant differences in composition and their potential relationship to disease risk, including colorectal cancer.
Marissa Shams-White, a senior population scientist at the American Cancer Society who was not involved in the study, concluded, “The findings suggest that simply classifying foods by their processing level may not tell the whole story. One of the challenges in studying ultra-processed foods is that this category encompasses a very wide range of food and drink, and we still do not know if all of them relate to colorectal cancer risk in the same way.”