Ultra-processed foods have long been under scrutiny for their potential effects on health, but new research suggests their relationship with colorectal cancer may be more complicated than previously thought. A large American study involving more than 460,000 adults found that overall consumption of ultra-processed foods was not associated with an increased risk of colorectal cancer. However, the findings reveal an important distinction: the types of foods people eat may matter more than how extensively they are processed.

Published on October 15 in PLOS Medicine, the study was conducted by Erikka Loftfield of the US National Cancer Institute and colleagues. The findings challenge the tendency to treat all ultra-processed foods as equally unhealthy, suggesting that their nutritional composition deserves greater attention.

Ultra-processed foods account for more than half of the calories consumed by American adults. They include everything from processed meats and packaged snacks to certain whole-grain cereals and dairy products. While some have been linked to increased health risks, others contain nutrients associated with better health outcomes, making broad dietary recommendations difficult.

To investigate these differences, researchers examined dietary information from 461,682 adults aged 50 to 71 who joined the NIH-AARP Diet and Health Study between 1995 and 1996. Participants completed questionnaires about their eating habits, allowing researchers to estimate their consumption of ultra-processed foods. Their health outcomes were tracked until 2018, with a median follow-up of 18.8 years.

The results showed no overall association between ultra-processed food consumption and colorectal cancer incidence. Yet a closer examination revealed contrasting patterns. Higher consumption of whole grains, fibre, dairy products and calcium from ultra-processed sources was associated with lower cancer incidence. In comparison, greater consumption of meat from these sources was linked to higher incidence.

Researchers also explored whether replacing ultra-processed foods with minimally processed alternatives could make a difference. They found that substituting 10% of ultra-processed food intake by weight with minimally processed foods was associated with a modest 2% reduction in colorectal cancer incidence, suggesting that dietary changes may still offer benefits.

However, the researchers urged caution when interpreting the findings. Most participants were older white Americans, limiting how broadly the results can be applied. Dietary habits were assessed only once, at the beginning of the study, meaning subsequent changes in food consumption and the growing availability of ultra-processed products were not captured. As an observational study, the research also cannot establish cause and effect.

The findings reinforce existing dietary advice rather than overturning it. Eating more whole grains, fibre-rich foods and dairy products while limiting processed meat remains consistent with colorectal cancer prevention recommendations. As Loftfield explained, although total ultra-processed food intake showed no association with colorectal cancer, differences between food groups followed established dietary guidance. The central message is that not all ultra-processed foods carry the same associations with cancer risk.

More information: Leila Abar et al, Associations of food processing and dietary risk factors with colorectal cancer incidence in the NIH-AARP Diet and Health Study: A cohort study, PLOS Medicine. DOI: 10.1371/journal.pmed.1005251

Journal information: PLOS Medicine Provided by PLOS