Diet and cancer: Current knowledge, methodologic pitfalls and future directions

Cancers in Australia in 2010 attributable to inadequate consumption of fruit, non-starchy vegetables and dietary fibre

Objectives

To estimate the number and proportion of cancers occurring in Australia in 2010 attributable to consumption deficits in fruit, non-starchy vegetables and dietary fibre.

Methods

We estimated the population attributable fraction (PAF) for cancers causally associated with inadequate intake of fruit and non-starchy vegetables (oral cavity, pharynx, oesophageal squamous cell carcinoma, stomach, larynx); inadequate intake of fruit (lung); and insufficient intake of fibre (colorectum). We used standard formulae incorporating prevalence of exposure (1995 National Nutrition Survey) and relative risks from independent studies.

Results

Overall, 1,555 (1.4% of all) and 311 (0.3% of all) cancers were attributable to inadequate intakes of fruit and non-starchy vegetables, respectively. A further 2,609 colorectal cancers (18% of colorectal) were attributable to insufficient fibre intake. If Australians increased their fibre intake by eating the recommended daily intakes of fruit and vegetables, an estimated 1,293 (8.8%) colorectal cancers could be prevented.

Conclusions

One in six colorectal cancer cases was attributable to inadequate intake of dietary fibre and about 1,800 cancers at other sites were attributable to insufficient fruit and non-starchy vegetable consumption.

Implications

Increasing the proportion of Australians who consume the recommended intake of fruit, vegetables and fibre could prevent up to 4% of all cancers.

Achievements and future of nutritional cancer epidemiology

We consider some of the earlier work and some recent results on diet and cancer (since the 2007 WCRF/AICR report on Diet and Cancer), discuss challenges facing nutritional cancer epidemiology, and consider the field from the perspective of the need to apply what we know in cancer control. We highlight 2 current difficulties; first, we are uncertain on the stage of carcinogenesis on which many nutritional factors act, second, we often do not know what dose of a nutritional factor is needed to achieve its expected protective effect in humans. Part of the difficulty is the measurement error associated with food frequency questionnaires. Calibration studies (as in the European Prospective Investigation on diet and Cancer) have helped to reduce this, and pooled studies have helped to clarify associations. However, there is too little work on new biomarkers of nutrition; with the new techniques available (especially proteomics, and metabolomics) it should be possible to identify more and better biomarkers that could be used in repeated blood or urine samples and give very good information on diet. In cancer control we need to determine how to reduce the prevalence of obesity and increase physical activity in populations, not whether they are causal factors. This could be achieved by community-based interventions linked to some of the new cohort studies being initiated. We conclude we have reached the stage in nutritional cancer epidemiology where we need to concentrate more on applying the lessons we have learnt, than in seeking new aetiological associations.