An international study has found no overall association between total ultra-processed food intake and bowel cancer risk in a cohort of nearly half a million US adults. However, further analysis of specific food groups showed some were linked to an increased risk of bowel cancer while other types were associated with a lower incidence of the disease.
Intake of ultra-processed meat was linked to higher bowel cancer risk, while intake of whole grains, fibre, dairy and calcium, from ultra-processed foods (UPFs) such as wholemeal bread and flavoured yoghurt, were associated with lower risk.
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.
Published in PLOS Medicine , the study supports current dietary guidance and highlights the diversity of UPFs and how they should not be viewed as a uniform group.
The research was led by Dr Erikka Loftfield while at the National Cancer Institute at the National Institutes of Health (NIH) in the United States, with collaborators from the US, Brazil, and Netherlands. Dr Loftfield now leads QIMR Berghofer’s Integrative Nutritional Epidemiology Group in Queensland.
Dr Loftfield said the team used the NIH-AARP Diet and Health Study which recorded the eating habits of more than 460,000 US adults in the mid-1990s and then followed them for nearly 20 years.
“In this very large cohort of US adults, we saw no association between total UPF intake and incidence of bowel cancer. However, when we looked at the specific food groups, the results were very different depending on the food type,” Dr Loftfield said.
“Even though the whole grain and dairy foods were highly processed, we found a higher intake of those foods and limited consumption of ultra-processed meat was linked to lower incidence of bowel cancer. This is in line with the existing dietary guidance for preventing bowel cancer.”
The association between the type of food group and bowel cancer was the same regardless of the extent of processing involved.
The research team used the globally recognised NOVA food processing classification system.
The NIH-AARP study data covers 461,682 US adults aged between 50 to 71 years who completed a food questionnaire in 1995-1996. Their health outcomes were then observed until 2018. During that time, 10,075 were diagnosed with bowel cancer.
The researchers stress this study cohort is primarily made up of older, white Americans so their findings should not be generalised to younger and diverse populations. The research also potentially underestimates actual UPF intake given increased availability of highly processed foods in recent years.
Greater understanding about the association between UPFs and chronic diseases like cancer is needed with more than half of the energy intake of US adults and around 40 per cent of Australian adults now coming from UPFs.
Dr Loftfield said the 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 next stage for the research would be to extend it to study 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.
The study is available in the open access journal PLOS Medicine with DOI 10.1371/journal.pmed.1005251
Dr Erikka Loftfield is researching diet-related causes of cancer to better prevent disease
