Ultra-processed foods showed no overall link to bowel cancer in 19-year US study

What the study found

A long-term study of more than 461,000 older American adults has found no overall link between total ultra-processed food intake and colorectal cancer risk.

Published in PLOS Medicine, the analysis tracked participants from the NIH-AARP Diet and Health Study over a median of 18.8 years. During the follow-up period, 10,075 people developed colorectal cancer. Researchers found that people consuming the highest fifth of ultra-processed foods had essentially the same risk as those consuming the lowest fifth.

However, breaking down the diet revealed that specific ingredients matter significantly more than industrial processing alone. Replacing 10% of ultra-processed foods with whole or minimally processed foods was associated with a 2% reduction in bowel cancer incidence.

Which foods increased or reduced risk

The impact on cancer risk varied sharply depending on the specific type of food consumed. Ultra-processed meats were linked to higher cancer rates, whereas whole-grain breads, high-fibre breakfast cereals, and dairy products like fruit yoghurts—which technically fall under ultra-processed classifications—were associated with lower cancer rates.

Researchers defined ultra-processed foods using the Nova classification framework, which categorises items based on the nature and extent of industrial processing. The study team noted that nutritional components such as fibre, calcium, and processed meat play a far stronger role in colorectal cancer risk than the processing label itself.

Study details and key limitations

The research was led by scientists at the National Cancer Institute in collaboration with Yale University, Brigham and Women's Hospital, Harvard Medical School, the International Agency for Research on Cancer, and institutions in Australia, Brazil, and the Netherlands.

The authors noted several limitations. Participants were between 50 and 71 years old when enrolled in 1995–96, meaning the findings may not explain the rising incidence of colorectal cancer among adults under 50. Dietary habits were recorded once at enrollment using a food frequency questionnaire, and the observational design means the study establishes associations rather than direct cause and effect.

Health advice from the American Cancer Society and the International Agency for Research on Cancer continues to recommend limiting red and processed meats, while maintaining a diet rich in whole grains and fibre.