Chips, instant noodles, sausages and frozen dinners have had a bad reputation for years, long before science began to examine their effects on health. Researchers have linked ultra-processed foods (UPFs) to heart disease, diabetes and other chronic conditions.
Colorectal cancer has been on that list, too. So, the fear surrounding UPFs makes sense. The evidence has only added to that fear. A new study of more than 460,000 US adults, however, challenges the idea that all packaged and processed foods carry the same risks. The study by researchers at the US National Cancer Institute found that overall UPF consumption was not associated with an increased incidence of colorectal cancer (CRC). The study is published in the journal PLOS Medicine.
What are ultra-processed foods?
Ultra-processed foods are grouped by how much industrial processing they undergo, and the category is huge. For instance, the loaf of sliced bread you buy falls into this category, as does a bag of crisps. Flavoured sparkling water and diet soft drinks can qualify, too. Confused? Here’s how to identify ultra-processed foods and understand what sets them apart. Ultra-processed foods are typically energy-dense products that are high in sugar, unhealthy fats and salt, and low in dietary fibre, protein, vitamins and minerals.
UPFs and the American diet
Ultra-processed foods supply more than half of the energy intake among US adults. This widespread consumption has drawn growing attention to potential links with chronic diseases, including colorectal cancer. However, UPFs represent a wide range of foods. Some, such as wholegrains and dairy products, are associated with a lower risk of CRC, while others, such as processed meats, are associated with a higher risk.To better understand these links, researchers at the US National Cancer Institute, led by Erikka Loftfield, analysed data from 461,682 adults aged 50 to 71 who were enrolled in the NIH-AARP Diet and Health Study between 1995 and 1996. Using a food frequency questionnaire, participants recorded their eating habits. This questionnaire helps researchers estimate UPF intake. The participants were followed until 2018, with a median follow-up period of 18.8 years.
The results
While increased UPF intake has been consistently linked to CRC, this study found no association between overall UPF intake and CRC incidence. However, the findings differed by food type. For instance, higher intakes of wholegrains, fibre, dairy products and calcium from UPF sources were associated with a lower incidence of CRC. Meat from UPF sources, however, was associated with a higher incidence.The researchers noted that replacing 10% of the gram weight of UPFs with minimally processed foods was associated with a 2% lower incidence of CRC.“In this large population of older US adults, we did not observe an association between total ultra-processed food (UPF) intake and colorectal cancer incidence; however, when we looked at food groups, like whole grains, dairy, and meat, by UPF or non-UPF source, we found that associations were in line with current dietary guidance for colorectal cancer prevention such that higher whole grain and dairy but lower meat intakes were associated with lower colorectal cancer incidence,” Loftfield said.However, the study also had some limitations. The study cohort included primarily older, white Americans and measured UPF intake only once, at baseline. Generalising these findings to younger and more diverse populations is therefore not ideal, the researchers cautioned. People change their eating habits over two decades, and UPFs have become more widely available. This could mean the study underestimated how much of these foods people actually ate.The study does not give anyone a licence to stop worrying about diet. It does, however, argue against treating every packaged food the same way. Bread, yoghurt and sausage may share a label, but they do not have the same effects on the body. The more useful question when choosing food is not simply ‘Is this ultra-processed?’ but ‘What is this food, and what is it replacing?’The study suggests that UPFs should not be treated as a monolith. It supports current dietary advice to eat more wholegrains, fibre and dairy products, and to limit processed meat to reduce the risk of colorectal cancer.