Ultra-Processed Foods and Bowel Cancer: New Insights from a Large-Scale Study
In recent years, ultra-processed foods (UPFs) have drawn significant attention for their potential health impacts. Many people worry that instant noodles, sausages, sugary drinks and other UPFs increase cancer risk. However, a major international study published in PLOS Medicine offers a more nuanced answer: not all ultra-processed foods are equally harmful, and different types of UPFs have very different effects on bowel cancer risk.
Study Overview: Nearly 500,000 Participants, 20 Years of Follow-Up
The research was led by Dr Erikka Loftfield while at the National Cancer Institute (NCI) at the National Institutes of Health (NIH) in the United States, with collaborators from the US, Brazil, and the Netherlands. Dr Loftfield now leads QIMR Berghofer's Integrative Nutritional Epidemiology Group in Queensland, Australia. The team used data from the well-known NIH-AARP Diet and Health Study, which included 461,682 US adults aged 50 to 71 who completed a food questionnaire in 1995β1996. Their health outcomes were then followed for nearly 20 years, until 2018. During that time, 10,075 participants were diagnosed with bowel cancer.
Key Findings: UPFs Are Not a Uniform Group
The study produced two critical conclusions:
- There was no overall association between total UPF intake and bowel cancer risk. In other words, simply looking at "how much ultra-processed food was eaten" does not directly predict bowel cancer risk.
- However, when specific food groups were analysed, the results were very different. Some UPFs were linked to increased risk, while others were associated with lower incidence of the disease.
Which UPFs Increase Risk? Which Lower It?
Using the globally recognised NOVA food processing classification system, the researchers found:
- Increased bowel cancer risk: Ultra-processed meat (such as sausages, bacon, and ham).
- Lower bowel cancer risk: Whole grains, fibre, dairy and calcium from ultra-processed foods, such as wholemeal bread and flavoured yoghurt.
Notably, the association between food groups and bowel cancer was the same regardless of the extent of processing involved. In other words, even "ultra-processed" wholemeal bread may still benefit gut health due to its whole grain and fibre content.
Replacing 10% of UPFs Linked to 2% Reduction in Bowel Cancer
The study also found that replacing 10 per cent of UPF intake with the equivalent weight of minimally processed foods was linked to a two per cent reduction in the incidence of bowel cancer. This suggests that even small adjustments to dietary patterns can bring tangible health benefits.
Expert Perspective: Diet Quality Is Key
Dr Loftfield emphasised that these findings should be viewed in the context of overall nutrition: "We know that diet quality is important for chronic disease prevention. Although we found that intake of ultra-processed whole grain and dairy products was linked to lower incidence of bowel cancer, those same foods may contain high levels of added sugars or salt which could increase the risk of other chronic diseases. The advice is to eat for overall health, prioritising foods that are nutrient dense and avoiding foods with high amounts of added sugars, salt, and saturated fat."
The research team also noted that the study cohort was primarily made up of older, white Americans, so the findings should not be generalised to younger and diverse populations. Additionally, the research potentially underestimates actual UPF intake given the increased availability of highly processed foods in recent years.
Practical Implications for Daily Eating
- Don't reject all UPFs outright: Wholemeal bread, high-fibre breakfast cereals, and unsweetened yoghurt can still be part of a healthy diet.
- Focus on limiting ultra-processed meat: Sausages, bacon, and ham should be eaten sparingly.
- Pay attention to overall dietary patterns: Eat more whole grains, vegetables, fruits, and fibre-rich foods; limit added sugars, salt, and saturated fat.
- Replace some UPFs with minimally processed foods: For example, swap sugary snacks for fresh fruit, or replace some convenience foods with home-cooked meals.
Next Steps for Research
The researchers say the next stage is to extend the study to different populations. Another important step would be to review the definitions of UPFs and ensure measurement is standardised among the nutrition and scientific community globally, so that the health effects of ultra-processed foods can be assessed more accurately.
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