Diet

Estimates for the percentage of cancer cases attributable to diet range from 5% of all cancer cases in the United States³ to 30% of cancer cases in European men.¹⁶,⁵⁷ Worldwide, it has been estimated that 374,000 cancer deaths each year can be attributed to low fruit and vegetable intake.⁵²

Diet in Australia

Many Australians do not include sufficient vegetables and fruits in their daily diets. Data from the 2011-12 Australian Health Survey indicate that only 5.5% of Australian adults had an adequate usual daily intake of fruit and vegetables.⁵⁸ While 48.5% of Australian adults reported that they usually met the guideline for daily fruit intake (2 serves per day), only 8.2% met the guideline for daily vegetable intake (5 serves per day).⁵⁸

Dietary fibre

Foods containing dietary fibre, such as vegetables, fruits, pulses (legumes) and cereals, are identified by the 2007 WCRF and AICR report and updates as having convincing evidence for a protective effect against colorectal cancer, with limited suggestive evidence for oesophageal cancer.^8-15 A recent meta-analysis of around 580,000 subjects indicated a protective association between dietary fibre and risk of gastric cancer.⁵⁹ The WCRF and AICR report recommends consuming at least 400 g of a variety of non-starchy vegetables and fruits every day, as well as including relatively unprocessed cereals (grains) and/or pulses (legumes) with each meal to reduce risk of cancer.⁸

Plant-based foods

The WCRF and AICR report and updates identified that the evidence for the protective effect of plant-based foods is less compelling than in the mid-1990s, when the previous WCRF and AICR report was published.⁸ The report and updates identified probable evidence that a diet rich in plant-based foods, such as fruit, vegetables and unprocessed cereals, reduces the risk of various cancers and likely protects against weight gain due to the low energy density of such foods.^8-15 Fruits and vegetables (particularly non-starchy vegetables) probably protect against mouth, pharyngeal, laryngeal, oesophageal and stomach cancers, and lung cancer (fruits only).^8-15 Limited suggestive evidence supports a protective effect of non-starchy vegetables and fruits for nasopharyngeal and colorectal cancers.^8-15 The WCRF and AICR also identified limited evidence suggesting that vegetables protect against lung cancer.^8-15 Data from the large EPIC study indicated a modest association between increased intake of total fruits and vegetables, notably intake of vegetables, and reduced overall cancer risk.⁶⁰

Overnutrition and weight gain

Overnutrition, i.e. overconsumption of calories and the weight gain it causes, has been identified as contributing greatly to cancer burden.² Consumption of additional calories from any source contributes to weight gain and increasing cancer risk.⁶¹ The WCRF and AICR report identified that increasing consumption of energy-dense foods and sugary drinks is probably contributing to the rise in overweight and obesity, which increases risk of certain types of cancer.⁸ The report recommends limiting energy-dense foods and fast foods, and avoiding sugary drinks to prevent and control weight gain, overweight and obesity.⁸

Red meat, processed meat and cancer

Data on meat consumption indicate that Australian males and females eat around 200 g and 120 g respectively of meat, poultry and game each day.⁵¹ The WCRF and AICR report and updates identified convincing evidence that increased consumption of red meat and processed meat increased risk of colorectal cancer, and limited evidence suggests increased risk of oesophageal, lung, pancreatic and stomach cancers.^8-15 Dose response meta-analyses have indicated a 17% increase in colorectal cancer risk for each 100 g increase per day in red meat, and an 18% increase in colorectal cancer risk for each 50 g increase per day in processed meat.¹⁰ The WCRF and AICR report recommends limiting consumption of red meat to less than 500 g per week, very little if any to be processed meat.⁸

Salt and cancer

The WCRF and AICR report identified evidence that salt (from salty foods, processed foods, and added salt) is a probable cause of stomach cancer.⁸ As processed foods are a major source of salt, the WCRF and AICR report recommends that individuals limit consumption of processed foods with added salt to ensure an intake of less than 6 g of salt per day⁸ (equivalent to approximately 2,300 mg sodium). The Nutrient Reference Values for Australia and New Zealand recommend an adequate intake of 460-920 mg of sodium per day for the adult population, and an intake of 2,300 mg of sodium per day is considered the upper level of intake that should not be exceeded.⁶²

Reducing individual risk of cancer and staying healthy

Some studies suggest that a diet with greater fruit and vegetable consumption may reduce the risk of becoming obese.^63-65 To reduce risk of cancer, the 2007 WCRF and AICR report recommends: limiting consumption of energy-dense foods and avoiding sugary drinks, eating mainly foods of plant origin, limiting intake of red meat and avoiding processed meat, and limiting consumption of salt and processed foods with added salt.⁸ The WCRF and AICR report indicates that dietary supplements are not recommended for cancer prevention.⁸ The report judges that food and drinks, rather than dietary supplements, are the best source of nourishment for the general population, and recommends aiming to meet nutritional needs through diet alone.⁸

The Australian Dietary Guidelines recommend a varied diet of nutritious foods, including vegetables, fruits, grains, dairy products, lean meat, fish and water, and limiting intake of foods with saturated fat, added salt and added sugars.⁵¹ The guidelines recommend consuming five servings of vegetables and two servings of fruit per day, and limiting meat consumption to 455 g of lean meat per week (i.e. up to 65 g per day).⁵¹

Cancer Australia recommendations for individuals

Cancer Australia recommends consuming adequate dietary fibre, including unprocessed cereals (grains) and pulses (legumes), and aiming for five servings of vegetables and two servings of fruit per day. Cancer Australia recommends limiting intake of red meat to less than 500 g per week and avoiding processed meat to reduce cancer risk. Cancer Australia recommends limiting intake of salt and processed foods with added salt to reduce cancer risk.

Table 4: Summary of evidence for diet and cancer sites

See Appendix 1 for explanation of evidence.