Cancer is one of the one of the leading causess of death worldwide. Growing evidence points to the impact of dietary habits on cancer risk. The good news is that 30–50% of all cancers could be prevented by making simple lifestyle changes, such aslike following a healthy diet.^{1, 2}

Did you know?

Diet-related chronic conditions are some of the leading causes of death and disability in Australia.³

In 2017-18, just over half of all adult Australians met the guidelines for the recommended daily serves of fruit (2 or more serves), while only one in thirteen met those for vegetables (at least 5 serves for women and 5-6 serves for men). Only one in twenty adults met both guidelines.³  

Cancer is a leading cause of illness in Australia, with over one million Australians currently living with or having survived cancer.⁴

While cancer survival rates have improved, cancer still accounts for about 30% of all deaths in Australia.⁴

In 2019, an average of 136 Australians per day were expected to die from cancer. ⁴

The Facts

Excess calories

• Studies have consistently shown that excess calories from any source lead not only to weight gain, but also to increased cancer risk.^{5, 6}
• After smoking and infection, obesity is the most significant risk factor for cancer globally.⁷ In fact, it is estimated that 20% of all cancers are caused by obesity.⁸

Red meat

• A high intake of red meat has been associated with an increased risk of colorectal cancer⁹ and cancer-specific mortality.^10. A working group of the International Agency for Research on Cancer (IARC) classified red meat as a Group 2A carcinogen, probably carcinogenic to humans, which means that there is an association but it may not be causal.⁹

Processed meat

• Processed meat is meat that has undergone fermentation, salting, curing, smoking or adding adding chemical preservatives, to preserve and increase its flavour. Examples include hot dogs, ham, bacon, ham, salami, beef jerky and some deli meats. 
• The IARC Working Group (the specialised cancer agency of the World Health Organization) has also classified processed meats as a Group 1 carcinogen – the same category as cigarette smoking, alcohol, asbestos and air pollution – meaning that there is convincing evidence that processed meat causes cancer.¹¹

Dairy products

• A recent study of women initially free of cancer found a correlation between consumption of dairy milk and increased risk of breast cancer when adjusted for soy intake (that is, results were adjusted to take into account any potential impact of soy intake on study results).  As little as ¼ to 1/3 cup of dairy milk per day increased the risk of breast cancer by 30%, 1 cup increased risk by 50%, and 2-3 cups increased risk by 70-80%.  No relevant associations were observed for cheese and yoghurt.¹²

Refined carbohydrates

• A diet high in sugar and refined carbohydrates raises blood glucose and insulin levels (both risk factors for cancer) and may increase the risk of breast and other cancers.^{13, 14}

Omega-3 fatty acids

• A meta-analysis of 19 trials showed that taking omega-3 fatty acid supplements did not affect the incidence of cancer.¹⁵
• Preliminary results from intervention trials show that a high intake of marine omega-3 fatty acids may improve outcomes in breast cancer diagnosis, reduce reoccurrence and improve survival.¹⁶ 
• A critical review of the effect of cancer patients taking omega-3 fatty acid supplements to treat secondary complications such as pain, depression, cachexia-anorexia and paraneoplastic syndrome shows promise due to their anti-inflammatory nature, but this needs further research.¹⁷ 

Fruits and vegetables

• Regularly eating fruits and vegetables is linked with a reduced risk of cancers at various sites.¹³
• An analysis of the Pooling Project of Prospective Studies of Diet and Cancer found that higher total fruit and vegetable intake was related to a lower incidence of oestrogen-receptor-negative breast cancer. Vegetable intake alone was associated with an 18% lower risk when comparing those who ate the most vegetables with those who ate the least.¹⁸

Soy products

• Studies have found lower rates of breast cancer in Asian countries. Results suggest that the earlier in life people start consuming soy, the lower the risk of breast cancer, with a 25-60% reduction of risk, even if soy intake is later reduced.¹⁹ This may explain why the Oxford-EPIC study found no association between breast cancer and soy isoflavones, as many subjects began consuming soy in adulthood.¹⁹
• Studies show that soy protein and isoflavones are protective against breast cancer and safe for breast cancer survivors.^{19, 20} Soy is also safe for those receiving breast cancer treatment and may even enhance the medication’s effect.²¹
• Consuming soy leads to better prognosis and survival rates, with the greatest benefits seen when more soy is eaten.²² Consuming soy also reduces the reoccurrence of breast cancer.¹⁹
• The American Cancer Society and the American Institute for Cancer Research agree that consuming soy products is safe for women with breast cancer.¹⁹
• The World Cancer Research Fund concluded that consuming soy foods may improve the prognosis of women diagnosed with breast cancer.¹⁹

Dietary Patterns:

Western diet

• The Western diet is typically high in processed and red meats, refined grains, soft drinks and sweets is linked to a higher colorectal cancer risk, whereas a diet high in fruits, vegetables, fish, poultry and whole-grain products is associated with a lower risk.^{23, 24}
• A cohort study found that diets high in ultra-processed foods (mass-produced packaged breads, packaged snacks, soft drinks, reconstituted meat products with nitrite preservatives, instant soups, frozen meals, etc.) were associated with greater than 10% increases in the risk of overall cancer and breast cancer.²⁵

Mediterranean diet

• The Mediterranean diet, typically high in fruits, vegetables, nuts, legumes, whole wheat bread, fish and olive oil, is high in antioxidants, anti-inflammatory nutrients and protective phytonutrients.²⁶
• These nutrients fight the degeneration of normal cells into cancer cells, their proliferation if they develop, and angiogenesis that feeds their development.²⁶

Vegetarian diets

• Vegetarians and vegans typically eat more vegetables, fruits, soy and whole grains, and less processed and overcooked foods, which have been linked to increased risk.^{13, 27, 28}
• A systematic review and meta-analysis of vegetarians and vegans showed an 8% and 15% lower risk of cancer, respectively.^{13, 29}
• In a study of cancer risk and mortality, all-cause mortality was 17% lower for a vegetarian diet than for a non-vegetarian diet.³⁰
• Vegetarian and vegan diets are associated with a lower risk of developing or dying from cancer.^{13, 29, 31}

What can we do about it

Maintain a healthy weight

---

Avoid processed meat

---

Limit or avoid red meat

---

Follow a plant-based dietary pattern, rich in fruits, vegetables, whole grains, legumes, nuts and seeds

---

Include soy products, such as tofu, miso and tempeh

---