Few nutrition claims have spread as widely as the idea that ultra-processed food is uniformly bad for you. A new analysis in PLOS Medicine, which followed more than 460,000 older Americans for nearly two decades, found that it is not that simple for one of the most common cancers. Total intake of ultra-processed food showed no link with colorectal cancer. What people ate within that category did.

The study, published on Oct. 15 and led by Erikka Loftfield of the US National Cancer Institute, drew new coverage this week, including a summary from ScienceDaily on Oct. 21.

What the Study Followed

The researchers analyzed data from the NIH-AARP Diet and Health Study, a large US cohort. Participants were followed for a median of 18.8 years, through 2018, and more than 10,000 developed colorectal cancer, according to a summary of the paper. Ultra-processed foods were defined using the NOVA system, which classifies food by how much industrial processing it has undergone, from fresh ingredients to industrial formulations.

The team compared diets at the start of the study with later cancer diagnoses, and also looked at specific food groups, such as whole grains, dairy and meat, divided by whether the food was ultra-processed or not.

No Overall Link

The headline finding was a null one. Total ultra-processed food intake was not associated with a higher incidence of colorectal cancer, the authors report. As Medical Xpress put it, the study suggests that these foods should not be treated as a single block.

The researchers also modeled a swap. Replacing 10% of the weight of a person's ultra-processed food intake with minimally processed foods was associated with a 2% lower rate of colorectal cancer. That is a small difference, and the paper presents it as an association, not a prediction of what would happen to any individual.

Not All Ultra-Processed Foods Are Alike

The more interesting results lie inside the category. Ultra-processed meat products, such as processed meats, were associated with a higher risk of colorectal cancer. Whole grains, dairy and calcium-rich sources were associated with a lower risk, whether or not they were ultra-processed, according to summaries of the study. The authors say the patterns are in line with current dietary guidance for colorectal cancer prevention, which stresses whole grains, fiber, dairy and calcium and limits processed meat.

An expert quoted in an article from Moffitt Cancer Center said she was struck that overall intake was not associated with the cancer, since people often hear these foods described as uniformly harmful. The risk, she said, relates not only to how foods are processed but also to their nutritional content.

How It Fits With Earlier Research

Results in this area have not been consistent. A 2022 analysis of three large US cohorts, published in the BMJ, found that high total ultra-processed food intake was associated with higher colorectal cancer risk in men, with no overall association in women, and that certain subgroups were linked to higher risk in both. A French cohort found no link for colorectal cancer, though the authors suggested small numbers of cases and short follow-up might explain it.

The new study is larger and longer than those, which gives its null result weight. It does not erase the others. Different cohorts, different food questionnaires and different ways of grouping foods can all produce different answers.

What the Study Cannot Say

The cohort was mainly older, white Americans, and diet was measured only once, at the start, the authors note. People's eating habits change over nearly two decades, so a single questionnaire is a blurry guide to what they ate for years. The design is observational, so it can show associations but not cause and effect. I have read summaries and the abstract rather than the full paper, and I did not see the underlying risk estimates for each food group.

The null result also does not say ultra-processed food is harmless for other conditions. This study asked about one cancer.

What It Means

The practical reading is narrower than some headlines suggest. For colorectal cancer, what you eat inside the ultra-processed category appears to matter more than the category label, and the familiar advice, more whole grains and dairy, less processed meat, still stands.

My view: the most useful contribution is a caution against single-label thinking. Blogerroom has written before about how observational findings can look different depending on the question and the sample, for example in the REM sleep study that tied more sleep to lower risk for 83 diseases. And for people already facing the disease, treatment advances such as the FDA's approval of Tecentriq for stage III dMMR colon cancer show how much of the work happens after prevention fails.

Anyone with questions about diet and cancer risk, or with symptoms such as blood in the stool or a change in bowel habits, should speak to a doctor. This article is general information, not medical advice.