Ami Simmonds is Research Funding & Science Activities Officer at World Cancer Research Fund International.
Our understanding of the link between what we eat and preventing cancer is growing. For example, we now know a considerable amount about the link between nutrients, foods and food groups (eg carbohydrates, dairy) and cancer risk – especially following the research we have reviewed for our Continuous Update Project (an analysis of the global evidence on diet, nutrition – including body composition – physical activity and cancer).
In addition to looking at single foods or nutrients on their own, however, more research is needed on the consumption of a combination of different foods (ie what a person normally eats as part of their diet) for us to better understand the link between what we eat and cancer risk and survival. This is known as an individual’s dietary pattern and is different to, for example, researching the link between one type of food (eg red meat) and a person’s cancer risk and survival.
Dr Jill Reedy gave a presentation on dietary patterns at the International Society for Behavioural Nutrition & Physical Activity (ISBNPA) Conference in Scotland in June. Dr Reedy leads the Dietary Patterns Methods Project, which analyses the link between dietary patterns and disease.
In order to conduct this research, the project aims to standardise various dietary indices (also known as scores), including the Mediterranean Diet Score, the Healthy Eating Index and the Alternative Healthy Eating Index, to enable researchers to use the scores across different populations. Dietary indices are one of the tools used to assess dietary patterns; they can be constructed based on a set of dietary recommendations and used to capture and score how well a person adheres to the recommendations.
Dietary patterns and cancer risk
Our Cancer Prevention Recommendations set out 10 lifestyle factors – including seven on diet – that can reduce people’s risk of cancer and other non-communicable diseases. In her presentation at the ISBNPA conference, my colleague, Dr Panagiota Mitrou, explained how our Cancer Prevention Recommendations have also been turned into a dietary index – the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) score – to enable researchers to assess the degree to which people adhere to our Cancer Prevention Recommendations and the health effects of doing so.
The WCRF/AICR score is an accumulation of points assigned for adhering – or not adhering – to each of the components of our Cancer Prevention Recommendations or sub-recommendations. The specific Cancer Prevention Recommendations components used to construct the score vary depending on the research question and the data available. Despite this variation in score construction, the WCRF/AICR score has been used in a number of studies investigating how closely people are adhering to our Cancer Prevention Recommendations, including among European, US, Mexican and Canadian populations.
Most of this research has shown that higher adherence to the Cancer Prevention Recommendations is associated with lower cancer risk and mortality. Dr Dora Romaguera and colleagues were the first group to publish a research paper on the WCRF/AICR score in 2012, for which they used six of our Cancer Prevention Recommendations (in men, with an additional ‘special’ recommendation on breastfeeding in women).
The findings were encouraging, as people who had greatest adherence to the Recommendations were found to have an 18% lower risk of developing cancer compared with those with the lowest adherence. Dr Romaguera and colleagues also applied this WCRF/AICR score to cancer survival research and found that greater adherence to our Recommendations before diagnosis was associated with improved survival in colorectal cancer patients.
Using an index developed from our Cancer Prevention Recommendations to assess dietary patterns poses a number of methodological challenges; some of these issues might prompt researchers to consider the following questions before constructing a score:
- Which Cancer Prevention Recommendations and sub-recommendations should be used to construct the score?
- What are the most appropriate Recommendations considering the geography and culture of the specific population under investigation?
- How do you assess whether an individual meets or does not meet a Recommendation?
- What is the health outcome being assessed, and were there any Recommendations previously associated with the health outcome of interest?
Cancer Prevention Recommendations to include in the score
We noted earlier that most studies so far have constructed the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) score using different combinations of Cancer Prevention Recommendations or sub-recommendations, and this variation can occur even when assessing the same outcome.
Take our Cancer Prevention Recommendation to eat a mostly plant-based diet as an example; this Recommendation encompasses vegetable, fruit, wholegrain and pulse intake. These four dietary components can be further divided into sub-recommendations and assigned points (whole or half points) for intake by:
- Weight or portion size of non-starchy vegetables and fruit
- Processed or non-processed grains or pulses
- Refined or non-refined starchy foods
- Starchy or non-starchy plant based foods
After considering some of the questions listed above, whether this particular Recommendation or the sub-recommendations, or any other of our Cancer Prevention Recommendations, are included in the score construction can be dependent on (but not limited to): the data available; the subjective interpretation of whether a recommendation is met or not; or differences in measuring the recommendation as well as differences in how the recommendations are categorised.
We know from our analysis of global research that there is strong evidence that there are ten cancers linked to being overweight or obese, and therefore it might be worth considering whether greater emphasis should be given to the Recommendation on maintaining a healthy body weight; however, this has not been reflected in the weighting of components within the WCRF/AICR score that has been used in previous published studies.
A better understanding of how different components of diet and other lifestyle factors are associated with the health outcome of interest might provide the basis for giving higher or lower weighting to score components. This would be important when considering any variation observed in groups of individuals who obtain similar adherence scores, but adhere to different score components (recommendations).
Despite the challenges in using dietary recommendations for developing indices, the National Cancer Institute has undertaken important work to standardise some of the existing indices, so that they can be compared across different populations and health-related outcomes. This vital work has the potential to inform clinical interventions and to shape policy globally; encouraging people to adopt the healthiest possible lifestyle to prevent cancer and other non-communicable diseases.