Daphne Katsikioti, our Research Interpretation Officer, explains why cancer prevention research must look at the bigger picture when it comes to food and nutrition.
Historically, much of the evidence on diet and cancer prevention has come from analyses focused on single nutrients and food rather than diet patterns and habits. However, people eat food not nutrients, so these cannot be considered in isolation but instead each food must be understood in the context of the others.
For example, nutrients or ingredients may be correlated through their shared occurrence in foods or behavioural intake patterns, or they may physiologically interact or share common or complementary biological mechanisms.
A key mechanism whereby diet can affect cancer risk is by influencing the likelihood of being overweight or obese; obesity is a recognised contributor to at least 12 different types of cancer. Examination of the diet as a whole, as is done in dietary patterns research, could also be more readily translated into dietary guidelines.
Distinct dietary patterns arise from different ways of eating which varies according to food preferences, ethnicity, culture and other factors. Some dietary patterns might be based on perceived health benefits or ethical considerations such as fasting or vegetarian and vegan diets.
Dietary patterns can also be based on guidelines or recommendations for prevention of specific diseases. Often healthier dietary patterns are also associated with certain lifestyle factors such as being physically active and not smoking. Research on dietary and lifestyle patterns aims to bring a more ‘holistic’ approach to cancer prevention rather than the historically more reductionist approach focused on individual foods and nutrients.
Furthermore, while there are several examples of dietary components that can increase the risk of cancer – such as alcohol – there are almost no examples of single nutrients or dietary components that directly decrease the risk of cancer, despite decades of research.
Measuring and defining different dietary and lifestyle patterns
The Mediterranean diet score is used to measure adherence to the Mediterranean diet, a diet typically rich in vegetables, legumes, fruit, nuts, cereals and olive oil and low in saturated fats. The derived score can then be analysed alongside health outcome data to identify associations.
The WCRF/AICR 2018 score measures adherence to our Cancer Prevention Recommendations and can be considered a diet and lifestyle pattern. Our Third Expert Report emphasises the benefit of treating the Recommendations as a whole instead of ‘pick and mixing’ Recommendations to suit. A growing number of independent studies show that the more closely people follow our Recommendations, the lower their risk of developing cancer.
Investigating dietary and lifestyle patterns
An increasing number of studies are trying to look at the totality of the diet, which is likely to have an interactive, synergistic and combined effect on health. In recent years, research has evolved to allow a clearer assessment of various dietary and lifestyle patterns associated with health risks; and it is becoming more and more evident that an integrated diet and lifestyle pattern of a healthy, balanced diet, adequate physical activity, and maintenance of a healthy weight will have a significant impact on reducing cancer risk.
Although for some cancers, such as breast and colorectal cancer, the literature is growing for specific dietary patterns, it remains a challenge to draw conclusions and make public health recommendations. This is because the methods used to define the different dietary and lifestyle patterns are not standardised and need improvement.
As part of our Continuous Update Project (CUP), we analysed the global evidence on dietary patterns and the risk of cancer. There were relatively few studies that specified a dietary pattern, and of those many used different definitions. It was therefore not possible to draw any firm conclusions on the available evidence, with the exception of only limited evidence that adherence to healthy dietary patterns may reduce the risk of cancers of the mouth, pharynx and larynx. However, there was more evidence that healthy dietary patterns such as the so-called ‘Mediterranean-type’ diet, together with higher levels of physical activity, protect against excessive weight gain. While unhealthy patterns such as the ‘Western-type’ diet – which is characterised by higher intakes of red and processed meats, refined carbohydrates and processed foods – increased risk.
Future research directions
One of the workstreams of the CUP Transition is focusing on gaining a better understanding of how diet and lifestyle can affect cancer risk. Future research should look at novel approaches to data collection, analysis and synthesis that could be used to capture the effect of dietary and lifestyle patterns on health outcomes, including both obesity and cancer risk.
New developments, such as biomarkers for diet patterns and novel statistical techniques, and a focus on mechanisms using novel techniques such as ‘omics’, could improve our understanding of the links between diet and cancer.