Around 35% of cases of breast cancer may be preventable through dietary and lifestyle modification. Whilst the role of dietary fat intake in breast cancer risk has received much attention, findings have been somewhat controversial, possibly because fat is a complex composition of many different types of fatty acid, all with very different structures and functions. Furthermore, cancer progression is a multi-step process involving a combination of events leading to either the activation or inactivation of specific target genes, with different fats modifying these genes differently.1 Thus, it is the type of fat, rather than fat itself, that should be considered when comparing to breast cancer risk.
Whilst fat intake should make up around 30% of energy intake, it is estimated that some Western diets represent 28%–42% of total energy consumed, and that this increase in fat intake appears to be related to breast cancer risk. However, because individual fatty acids have conflicting effects on this risk, simply advising people to cut down on dietary fat may be misleading; advice should concentrate on both reducing total fat intake and advising on dietary changes of specific fats. This is because over the past 50 years qualitative changes in the type of fatty acid consumed appear to be of significance. These changes are specifically characterised by an increased consumption of saturated fat (especially from animal sources), trans-fats and vegetable oils rich in the omega-6 fatty acid linoleic acid.
The ‘right’ and ‘wrong’ types of fat
More specifically, the Western diet contains a disproportionately high amount of omega-6 and low amount of omega-3, and the resulting high omega-6:omega-3 ratio is thought to contribute to cancer through the excess production of inflammatory bi-products from the omega-6 family. Certainly, women who have reported consuming high levels of omega-6 and low levels of marine-derived long-chain omega-3 have been found to be at a twofold increased risk for breast cancer compared to women consuming high levels of marine-derived long-chain omega-3 and lower levels of omega-6.2 The omega-3 eicosapentaenoic acid (EPA), is considered to be protective through its ability to suppress the development of cancerous tumours not only directly, but also indirectly through inhibiting the production of new blood vessels within the tumour, thereby helping to ‘starve’ the tumour.4,5
How to redress the balance
A direct way to increase levels of EPA is through the consumption of oily fish, such as sardines, mackerel or salmon. Unfortunately, due to contamination issues with compounds such as dioxins and methyl-mercury, fish consumption as a source of omega-3 is becoming a less viable method of increasing omega-3 levels to concentrations of a therapeutic dose. However, the use of purified, highly concentrated EPA supplements as an alternative to consuming oily fish not only allows a safe and convenient adjunctive method of increasing omega-3, but also delivers the concentrations needed for a therapeutic response. Given that omega-3 deficiencies are not only related to cancer risk, but also to a myriad of conditions involving both immunity and inflammation, realising the need to restore a balanced omega-6:omega-3 ratio through supplementation is of huge importance to health. Certainly, epidemiological studies support the use of omega-3 supplements, and women who regularly take fish oils may be less likely to develop breast cancer when compared to women who do not supplement.5
Dr Nina Bailey is a nutritional scientist whose efforts are concentrated within the role of dietary health and nutritional intervention in disease, with particular emphasis being placed upon the role of essential fatty acids in conditions such as chronic fatigue syndrome and depression. Dr Bailey regularly holds training workshops both with the public and practitioners, and more information can be found on her website at www.drninabailey.com
References: 1. Fay, M.P. et al. Effect of different types and amounts of fat on the development of mammary tumors in rodents: a review. Cancer Res 57, 3979-3988 (1997).
2. Murff, H.J. et al. Dietary polyunsaturated fatty acids and breast cancer risk in Chinese women: A prospective cohort study. Int. J. Cancer n/a-n/a (2010).doi:10.1002/ijc.25703
3. Wendel, M. & Heller, A.R. Anticancer actions of omega-3 fatty acids–current state and future perspectives. Anticancer Agents Med Chem 9, 457-470 (2009).
4. Spencer, L. et al. The effect of omega-3 FAs on tumour angiogenesis and their therapeutic potential. Eur. J. Cancer 45, 2077-2086 (2009).
5. Brasky, T.M. et al. Specialty supplements and breast cancer risk in the VITamins And Lifestyle (VITAL) Cohort. Cancer Epidemiol. Biomarkers Prev 19, 1696-1708 (2010).