August 7, 2019

expert reaction to study looking at red meat and poultry consumption and breast cancer risk

Research, published in the International Journal of Cancer, reports that red meat consumption may increase the risk of breast cancer in women, whereas poultry consumption may have protective affects. 

Dr Clare Shaw, Consultant Dietitian in Oncology, The Royal Marsden NHS Foundation Trust, said:

“Whilst the research study is of good quality, I hold some reservations about the press release – and advise that reporting should exercise caution around some limitations in the publication.

“The press release fails to accurately acknowledge the multiple other factors – such as amount of physical activity, alcohol consumption and smoking – which are mentioned in the paper.  Once these were taken into account there was not a significant association between red meat and an increased risk of breast cancer (Table 2).  It is also important to highlight that the group of women in the study all had close relatives that had been diagnosed with cancer.  This in itself could be a significant factor and should be acknowledged.

“The study is an association/correlational relationship, rather than one of cause and effect.  Additionally only one questionnaire was carried out at the beginning to ascertain dietary intake.  The participants were not then assessed for seven years.  Whilst the initial questionnaire appears rigorous it is surprising that there is was no data captured throughout the subsequent seven years, and again caution should be exercised here.

“Equally the study included models of what would happen if some substituted one type of meat for another, something that was not perhaps reflective of the real world.  This did not happen in practice nor did the women undergo any further assessment of their poultry or meat intake.  Therefore it is inaccurate to suggest that poultry is ‘protective’ against breast cancer.

“In the study some of the groups of women were consuming high meat diets, i.e. consuming more meat than is recommended by the World Cancer Research Fund 2018 report and recommendations of 350 – 500g cooked meat per week.

“There are a number of factors that are associated with an increased risk of breast cancer, which are supported by stronger evidence – including factors like body weight.  These associations can be different for pre- and post-menopausal women.”

Prof Paul Pharoah, Professor of Cancer Epidemiology, University of Cambridge, said:

“This is yet another observational cohort investigating the association between different dietary components and cancer risk.  Weak associations were found between red meat consumption and an increased risk of breast cancer and between poultry consumption and a decreased risk of breast cancer.

“As always is important to remember that association (or correlation) does not imply causation.

“The authors use language in the press release and in the paper that implies causation – for example “While the mechanism through which poultry consumption decreases breast cancer risk is not clear” suggest – but causal associations have not been established.

“Associations as weak as these can easily be cause by small biases in the study design.  For example, these analyses have been adjusted for a large number of other risk factors and this may cause a phenomenon known as sparse data bias that results in spurious associations.

“Associations as weak as these may also simply be due to correlation of meat or poultry consumption with other risk factors.  This is known as confounding.  While the authors did adjust for many possible confounders it is unlikely to have eliminated confounding entirely and this seems a highly likely explanation for the findings.

“While there are many reasons to reduce red meat intake, the data from this study are of limited relevance to people making dietary choices.”

Dr Mieke Van Hemelrijck, Reader in Cancer Epidemiology, King’s College London, said:

“This study shows an association between red meat intake and risk of breast cancer, which potentially helps us generate further hypothesis around how breast cancer may develop.  However, it’s important to note that these risks are reported as relative risks, not absolute risks – which means that although the relative risk is a 23% increased risk compared to those who have a lower intake of red meat, the absolute risks are small.  Another limitation is that the cohort in the study is based on women who have a sister with breast cancer – so we can’t be sure whether these findings apply to the general population.

“Even though this is a large observational study, the findings cannot claim causality – so we can’t say from this study whether more red meat causes increased breast cancer risk, or that replacing red meat with poultry causes a reduced breast cancer risk; other factors may be at play.  But the results could be used to help us further understand how diet may have an influence in the development of cancer.”

‘Association between meat consumption and risk of breast cancer: Findings from the Sister Study’ by Jamie J. Lo et al. was published in the International Journal of Cancer at 05:01 UK time on Wednesday 7 August 2019. 

DOI: 10.1002/ijc.32547

Declared interests

Dr Mieke Van Hemelrijck: “No conflict of interest.”