Preventing cancer caused by unhealthy diet and excess weight

A healthy weight and diet are key to preventing many cancers (1,2). In 2019, it was estimated that almost 8% of all cancer deaths in Aotearoa/New Zealand were due to unhealthy diet, and more than 6% were due to high Body Mass Index (BMI) (3). But this burden is not the same for everyone, with Māori disproportionally and unfairly impacted by unhealthy diet, weight and food environments, and therefore weight-related cancers (4,5).

Strong food and nutrition policy as well as government action to enable access to affordable, sustainable and healthy food for all New Zealanders will help to reduce cancer risk and related inequities.

Diet, weight and the link to cancer

High BMI and cancer

Strong evidence shows that having a high BMI in adulthood is a cause of 13 different types of cancer (6). These are oesophageal (adenocarcinoma), stomach (cardia), pancreatic, gallbladder, liver, colorectal, breast (postmenopause), ovarian, endometrial, kidney, multiple myeloma (a type of blood cancer), meningioma (a type of brain cancer) and thyroid cancer.

Diet and cancer

Having a healthy diet reduces the risk of cancer. This is partly due to the direct effects of certain nutrients or foods that are associated with the risk of some cancers. However, the main effect of diet is due to its relationship with weight (1,7). Overall diet is more important than any one food, food group or nutrient, but there are some specific foods which directly affect cancer risk.

Strong evidence shows that:

• eating whole grain foods and foods high in dietary fibre such as fruits and vegetables reduces the risk of bowel cancer (8)
• eating dairy products reduces the risk of bowel cancer (9)
• eating processed meat increases the risk of bowel cancer (9,10).

In addition, there is strong evidence to show that sugar-sweetened drinks, refined carbohydrates and high-calorie foods increase the risk of excess weight gain (1,7).

We support the World Cancer Research Fund’s 10 recommendations to reduce the risk of developing diet- and weight-related cancers (11). 

Food environments and the link to cancer

The world we live in shapes the food we can regularly access and eat, and this in turn influences our body weight. What we eat largely depends on what healthy or unhealthy food options are easily available to us, how much healthy foods cost relative to unhealthy foods, and how those foods are advertised, as well as other factors including income, employment, education, working conditions and living conditions (5).

Historical injustices including loss of ancestral lands and traditional food sources, and unfair systems have contributed to Māori being more burdened by unhealthy food (12), associated weight gain and ultimately cancer (13). Other factors also contribute to this unequal burden of disease. These include more household food insecurity among Māori tamariki/children (14) and more fast food outlets in socio-economically deprived areas, where more Māori live (15). Māori children are also more exposed to unhealthy food marketing than non-Māori children (16).

These wider systemic and environmental impacts are key contributors to our current diet- and weight-related cancer statistics and they are also integral to addressing them.  

Cancer Society recommendations

Strong government leadership, regulation of the food supply and appropriate resourcing to enable access to affordable, sustainable and healthy food for all New Zealanders will help to reduce our cancer risk. This supports the Crown’s Te Tiriti o Waitangi obligations to protect the health and wellbeing of Māori (17).

The Cancer Society wants to see urgent improvements to the unhealthy food environments in which New Zealanders live, work, learn and play. We recommend population strategies, rather than individually focussed strategies, as the most cost-effective way to equitably address diet- and weight-related cancer risk in Aotearoa/New Zealand.

In accordance with leading health authorities, the Cancer Society recommends the following policy interventions and improvements to the current food system: 

1. Improving public awareness of the direct and indirect links between diet and cancer to encourage support for nutrition policy reform with a clear equity focus.
2. The government creates policies (e.g., for wages, taxes, welfare and housing) that ensure low-income households can afford a healthy diet without relying on grants or food parcels.
3. Development of a government-led Food and Nutrition Strategy that upholds Te Tiriti o Waitangi to clearly identify and address food systems that support culturally appropriate, sustainable and affordable healthy food to be easily accessible for all New Zealanders.
4. Regulations to protect tamariki/children and rangatahi/adolescents from exposure to unhealthy food marketing.
5. A comprehensive school food and nutrition plan to make healthy food easily available in all schools and early childhood learning centres. This should include healthy food and drink as policies and expansion of the Ka Ora, Ka Ako Healthy Schools Lunch programme.
6. Adoption of a substantial sugar-sweetened drinks levy (e.g. 20%) in line with national and international recommendations to encourage sugar-sweetened drink reformulation and reduced consumption.
7. Strengthening the existing Health Star Rating system and making it mandatory.
8. Government-led food reformulation, including mandatory targets to reduce sodium, added sugar and saturated fat content of processed foods, and overall food supply goals.

References

1. Wild CP, Weiderpass E, Stewart BW, editors (2020). World Cancer Report: Cancer Research for Cancer Prevention. Lyon,France: International Agency for Research on Cancer. Available from: http://publications.iarc.fr/586. Licence: CC BY-NC-ND3.0 IGO.
2. World Cancer Research Fund/American Institute for Cancer Research. Diet, Nutrition, Physical Activity and Cancer: A Global Perspective. Continuous Update Project Expert Report 2018. Available at dietandcancerreport.org
3. 2019. GBD Results Tool –For all ages and sexes; risk factor mortality for all cancer (neoplasms), New Zealand. Institute for Health Metrics and Evaluation. URL: http://ghdx.healthdata.org/gbd-resultstool?params=gbd-api-2019-permalink/2bf916c6c5fc6390404cc2bedf64add9 (accessed 24 October 2021).
4. Ministry of Health. NZ Health Survey 18/19. https://www.health.govt.nz/publication/annual-update-key-results-2018-19-new-zealandhealth-survey.
5. Te Aho o Te Kahu. 2022. Pūrongo Ārai Mate Pukupuku, Cancer Prevention Report. Wellington: Te Aho o Te Kahu, Cancer Control Agency.
6. IARC (2018). Absence of excess body fatness. IARC Handb Cancer Prev. 16:1–646. Available from: http://publications.iarc.fr/570.
7. World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Report 2018. Body fatness and weight gain and the risk of cancer. Available at dietandcancerreport.org
8. World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Report 2018. Wholegrains, vegetables and fruits and the risk of cancer. Available at dietandcancerreport.org
9. World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Report 2018. Meat, fish and dairy and the risk of cancer. Available at dietandcancerreport.org
10. IARC (2018). Red Meat and Processed Meat IARC Monographs 114. 1-517. Available from: https://publications.iarc.fr/Book-And-Report-Series/Iarc-Monographs-On-The-Identification-Of-Carcinogenic-Hazards-To-Humans/Red-Meat-And-Processed-Meat-2018
11. World Cancer Research Fund. Cancer Prevention Recommendations. Available at: https://www.wcrf.org/diet-activity-and-cancer/cancer-prevention-recommendations/
12. Ministry of Health. 2022. Adults’ Dietary Habits – Findings from the 2018/19 and 2019/20 New Zealand Health Survey. Wellington: Ministry of Health.
13. Te Aho o Te Kahu. 2021. He Pūrongo Mate Pukupuku o Aotearoa 2020, The State of Cancer in New Zealand 2020. Wellington: Te Aho o Te Kahu, Cancer Control Agency.
14. Ministry of Health. 2019. Household Food Insecurity Among Children in New Zealand. Wellington: Ministry of Health.
15. Vandevijvere S, Sushil Z, Exeter DJ, et al. 2016. Obesogenic retail food environments around New Zealand schools: a national study. American Journal of Preventive Medicine 51(3): e57–e66.
16. Signal LN, Stanley J, Smith M. Childrens everyday exposure to food marketing: an objective analysis using wearable cameras. Int J Behav Nutr Pyhysical Act. 2017;14(137).
17. NZ Government. Pae Ora (Healthy Futures) Bill. Wellington NZ. Available at https://legislation.govt.nz/bill/government/2021/0085/latest/LMS575405.html