Today, researchers from Cancer Grand Challenges team PROSPECT published an analysis they carried out as part of their work investigating the global rise of bowel cancer cases in younger adults. It looked into consumption of ultra-processed foods (UPFs) and their potential connection to bowel polyps, small growths that can sometimes develop into bowel cancer if they’re left untreated. 

The analysis found that nurses in the US who reported eating the highest amounts of UPFs had a higher risk of developing bowel polyps before age 50 than those who reported eating the lowest amounts of UPFs. 

This finding will help guide the next stages of the PROSPECT team’s research into the possible causes of early-onset bowel cancer (bowel cancer diagnosed before age 50). It’s a piece of a bigger puzzle, but it’s important not to forget how much is still missing. 

As we explained last year, there isn’t enough evidence to say that UPFs directly cause cancer. This analysis looked at the risk of polyps, rather than bowel cancer risk, so it’s a long way from changing that. 

There are likely many different factors contributing to the rise of bowel cancer in younger adults in the UK. It will take time to identify them and work out the role each might play. Studies like this need to be put in context, but they can help us get closer to understanding those factors, and, ultimately, to preventing more cases of early-onset bowel cancer. 

So, what can we take from this analysis in particular? In this article, we’ll be looking into how it worked, what it found and what it means for our research and our diets.

First, what are ultra-processed foods? 

The term ultra-processed foods comes from the NOVA food classification system, developed by researchers at the University of São Paulo, Brazil. UPFs are typically ready-to-eat or ready-to-heat foods with a long shelf life. Because of this, UPFs are often less expensive and more readily available than less processed, whole foods. 

How did the analysis work? 

The researchers repurposed data they collected from a long-running study of female nurses in the US, who were all aged between 25 and 42 when the study started. 

Over several decades, participants answered questions about a wide range of health and lifestyle factors, including whether they’d had a lower endoscopy (a test that looks at the inside of the large bowel). 

Participants also completed food-frequency questionnaires every four years between 1991 and 2015. This meant answering questions around how often they had eaten UPFs (and other foods) over the preceding year. 

To carry out their analysis, the researchers looked more closely at data on around 29,100 women who’d had a lower endoscopy before age 50. In every case where an endoscopy found polyps, the team checked medical records to confirm the diagnosis and identify the type of polyp. 

Bringing this information together allowed the researchers to explore whether UPF intake was linked to the risk of developing bowel polyps before the age of 50. 

This was a clever way of building on existing data to make it suitable for a new research question. However, because this was a US study that wasn’t originally designed to answer questions about UPFs, we need to be a bit cautious about interpreting the results for a UK population. We’ll come back to that. 

What did the analysis actually find about UPFs and bowel polyps? 

In this analysis, women who ate the most UPFs had a 45% higher risk of developing conventional adenomas – a type of polyp that can sometimes progress to cancer – compared to those who ate the least UPFs. In total, around 1 in 25 women in the sample developed these polyps. 

No such link was found for serrated lesions, another type of polyp that was investigated in the study. 

The study didn’t look at bowel cancer, and its findings don’t prove that UPFs directly cause polyps, but they do add to the growing evidence around diet and cancer risk. 

As PROSPECT co-lead Dr Andrew Chan puts it, “Our study suggests that reducing intake of UPFs may be one way to help reduce the risk of developing polyps.” 

That’s something PROSPECT and other researchers will keep investigating. 

“More research is needed to confirm this link,” explains Chan, who works at Massachusetts General Hospital in the US. “This means looking at larger and more diverse groups of people and investigating how the body responds to these foods to understand their role in early changes in the bowel.” 

A few things to note about the study… 

Coming back to those limitations – how confident can we be in the results of this analysis and its relevance to people in the UK? 

Firstly, it’s really difficult to accurately measure what people eat, and the use of food-frequency questionnaires in this study poses some problems. How well could you remember how often you ate different foods over the past year? 

Secondly, the analysis only included female nurses, who were predominantly white, from the US, and reported having a lower endoscopy before the age of 50. That’s a very specific group, and it’s not representative of the whole UK population. 

Thirdly, we know the food environment in the US is different to the UK, especially when it comes to UPFs. There are key differences in the foods we eat, the ingredients they contain and the way that they’re produced. Therefore, the findings from this analysis may not be applicable for the UK. 

Finally, as we’ve pointed out already, the outcome being investigated here isn’t bowel cancer – it’s bowel polyps. Though polyps can sometimes develop into cancer if they’re not treated, a study with this focus will always leave gaps in our knowledge about bowel cancer itself. 

So, what does this mean for research? 

These findings aren’t strong enough for us to draw conclusions about a link between UPFs and the risk of early-onset bowel cancer in the UK. 

However, as Chan explained above, they do suggest it’s worth exploring the potential link between UPFs and bowel polyps in other population groups, including in the UK. 

For team PROSPECT, only a year into its five-year funding period, that’s a valuable outcome. 

“This study shows some of the PROSPECT team’s work in action, helping shed light on how diet and other factors are associated with gut health and changes in the bowel linked to cancer risk,” says Cancer Grand Challenges Scientific Committee Chair and Cancer Research UK’s Chief Clinician, Professor Charles Swanton. 

“While causation hasn’t yet been demonstrated, researchers around the world in the PROSPECT team are combining large-scale population studies with cutting-edge lab science to build a clearer picture of the factors that may be contributing to this trend, and how we might help reduce it in future generations.” 

And what does it mean for our diets?

When it comes to diet and cancer risk, what you eat overall day-to-day is more important than individual foods or ingredients. Aim to eat a healthy, balanced diet with lots of fruit, vegetables and wholegrains and cut down on processed and red meat and foods that are high in fat, sugar and salt. 

Many UPFs are high in fat, sugar and salt, so it’s worth trying to cut down on these too, but a balanced diet will still probably contain the occasional less healthy or ultra-processed food. As long as you’re eating lots of wholegrains, fruits and vegetables and keeping a healthy weight, there’s no need to worry. 

Our diets are also heavily shaped by the world around us. Food prices, marketing and local availability can all make healthy choices harder, and they affect some groups more than others. We need broader changes – from food policy to public health initiatives – to make healthier diets more accessible for everyone.