How do we know what cancer prevention information to trust?

A woman looking confused

Every morning at World Cancer Research Fund (WCRF), our communications team looks at the day’s papers for stories related to our research investigating the links between diet, nutrition, physical activity, body weight and cancer.

They find numerous news articles about these topics, such as a new diet that is billed as being able to bring about weight loss, or a single food item that can protect against cancer.

At the same time, our science team makes sure that we are aware of all the newest cancer- and health-related research. As I write this, a quick search of PubMed (a searchable site of published health and medical papers) using the terms “diet and cancer” produces over 50,000 papers, while a search for “alcohol and cancer” brings back nearly 90,000 papers.

Social media has also given us access to health-related information from a variety of sources about treatments, supplements, and diets, often with limited reporting about how their benefits have been evaluated.

With so much information available, how can we know what information to trust to best benefit our health? And – as an organisation that investigates the associations between various risk factors and cancer – how does WCRF make sure that our recommendations are rooted in the available and best scientific evidence?

This is also a topic of considerable interest to the Academy of Nutrition Sciences (ANS) and WCRF has recently joined forces with them to respond to a letter published in The Lancet.

WCRF: providing cancer-related recommendations for the public

Since 1982, WCRF has been at the forefront of exploring the links between diet, nutrition, physical activity, body weight and cancer. When our first expert report was published, the associations between these factors and cancer were not widely understood – with many commentators questioning whether they truly had an impact upon the disease.

Since that time, the evidence base has increased significantly and WCRF has used this to undertake reviews of the evidence, draw conclusions, and make recommendations.

Alongside our reports which detail the results of our reviews, we also publish reports on the methods we use. This transparency means that the public, scientists, and policy makers can trust that our work is undertaken in a rigorous and structured way.

The Academy of Nutrition Sciences

The Academy of Nutrition Sciences (ANS) was established in 2019 to provide a collective voice for the nutrition science discipline, including those engaged in research, education and training, clinical practice, and nutrition science communication.

The Academy has a strong interest in nutrition research excellence, development of the nutrition science discipline, and application of the outcomes of rigorous nutrition science for public benefit, as demonstrated by its first position paper published in the British Journal of Nutrition.

The Academy results from a longstanding collaboration between four organisations: the Association for Nutrition; the British Dietetic Association; the British Nutrition Foundation; and the Nutrition Society.

The Academy also seeks to reduce the levels of misinformation about nutrition and health and improve the public’s understanding of how evidence is scrutinised and evaluated by organisations, like WCRF, to produce recommendations.

CUP/Global Cancer Update Programme

WCRF’s research programme, the Global Cancer Update Programme (CUP Global) analyses the evidence on how diet, nutrition, physical activity, and body weight impact the development of cancer and survival from the disease.

Within CUP Global, researchers at Imperial College London have produced a database containing approximately 10,000 papers (140 scientists from 17 different countries have contributed to our reviews) on this subject.

The researchers undertake reviews of these papers and report the sum total of their results – rather than results from individual papers. A panel of experts, including epidemiologists, clinicians and other cancer-related scientists, then uses the collected research and reviews to produce our Cancer Prevention Recommendations.

Only when the research shows there is a strong (convincing or probable) link between an element of our diet, physical activity or body weight and cancer will the panel make a recommendation.

By working in this way, we ensure that our recommendations consider the entire scientific evidence base. At the same time, the public can be confident that we only include elements in our recommendations that have an established benefit to our health and reduce our risk of cancer.

Our joint letter in The Lancet

For the recommendations made by organisations, such as WCRF, to be trusted by everyone who uses them, it’s essential that the underlying studies that we review appropriately and effectively analyse the available data.

The study investigators also need to document these methods and explain any changes clearly. Transparency about the assumptions made in arriving at the published findings is critically important.

Recently WCRF and ANS worked together to publish a letter in The Lancet about the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD 2019). Our letter joined calls from other scientists for the GBD 2019 investigators to reconsider the measurements they were using to draw conclusions about the links between dietary risk factors and diseases, including cancer.

Of particular interest to us was the dramatic change in the reported impact of eating unprocessed meat upon health. In 2019 the GBD study reported that 896,000 deaths were caused by a diet high in red meat, a dramatic change from only 25,000 deaths in 2017.

It seemed to us that this change had more to do with the method used to estimate risky levels of meat eating, rather than changes in how eating it was impacting health.

For both WCRF and ANS, our biggest concern is that many users of the valuable data provided by GBD, will not be aware of the technical details which underlie this change, with risk of unintentional misinterpretation.

It’s important that challenges – such as those made in the Lancet letter from the scientific community – are quickly and openly addressed so that the public, scientific community and policy-makers can have faith in the results of published research.

This is particularly true for studies like GBD, because they play a key role in establishing the scientific base for public health policy and disease prevention efforts.

We’re therefore pleased to note that – at the time of this blog post going online – the GBD investigators had already responded to the concerns from the scientific community, by publishing a letter detailing how they intend to change and improve their methods for GBD 2020.

WCRF and ANS understand the increasingly-complex body of evidence demonstrating links between diet and health outcomes. We look forward to reading the results of GBD 2020, which incorporate adjustments to the methodology, and welcome the investigators’ transparency.

> Read more about the Global Cancer Update Programme

> View our Cancer Prevention Recommendations