EXPERT REACTION: Poultry protection - Eating chicken may defend against breast cancer

The study suffers from the disadvantage of relying on a single questionnaire completed only at the beginning of the study period for its dietary information. However, the study has the advantage of involving a large number of women (>42,000), all with a family history of breast cancer, followed for an average of 7.6 years. The researchers have also corrected the results for a number of likely confounding factors, including obesity, age, income, educational level, total energy intake, percentage of energy from fat, consumption of vegetables, fruit and dairy products, how long they breast-fed infants and the women's use of hormone therapy.

The fact that they found a relationship between invasive breast cancer and a high consumption of red meat once all these factors have been included cannot be dismissed. The lowest quartile of intake was 340g a week; the highest was 775g or more. The relative safety of a modest intake of red meat (as shown in the lowest quartile) is in tune with various recommendations for safe levels of red meat consumption for minimal occurrence of other health problems. The fact that poultry appeared 'safe' offers an alternative for other meals.

This is a large epidemiological study to examine the effect of meat consumption on breast cancer risk on women who have a family history of breast cancer.

The most important point to note is this study is part of the US/Puerto Rico-based Sister Study in which participants have a sister or half-sister that has been diagnosed with breast cancer.

Therefore any observations from this study needs to keep this in mind, that the observed results may not reflect women who have no family history of breast cancer.

It is a very large study (n=42, 012 women; breast cancer diagnoses = 1,536 women) with a reasonable follow-up time of 7.6 years, though it would have been good to have a longer time frame.

It is done in American/Puerto Rican women and is consequently skewed to non-Hispanic white women

It comprehensively accounts for various confounding factors (BMI, race, income, education level, vegetable/fruit intake, exercise etc) in their statistical models when assessing the amount of meat consumption in relation to subsequent breast cancer diagnoses.

There is no control group of women who didn’t eat meat. This is a weakness in the study because it can’t be determined if eating any form of meat could potentially increase or decrease breast cancer risk. This study simply shows that eating more red meat increases breast cancer risk or eating less poultry decreases breast cancer risk (in women with sisters with breast cancer)

There is conflict in the scientific literature about whether red meat consumption is a risk factor for breast cancer. Therefore despite the stated 23% higher risk between the highest and lowest red meat-eating groups, this study can’t accurately determine what the actual risk of women consuming red meat is for their breast cancer risk.

A similar observation can be made for the observed reduction in breast cancer risk in women who ate more poultry compared to the lowest poultry consumption group.

I would like to reiterate that these narrowly-defined increased or decreased risks must not be put onto the general population since we don’t know the actual risk for breast cancer with the general population is.

The authors of this paper have acknowledged the limitations in the study.

This is a very interesting study, however it’s important not to over-react. The research isn’t saying that red meat is bad for us, just that a large intake of red meat may be. I do believe that it’s worth checking your red meat consumption and ensuring that you’re not consuming over the maximum recommendations of 455g per week.
 
As a dietitian I’m often asked whether chicken is a cancer risk. This study suggests that it is safe to eat as part of a healthy diet.

This study has specifically looked at the consumption of different types of meats and the way they are cooked on the incidence of breast cancer in 42,012 women enrolled in the Sister Study. Previous research in this area has not been conclusive regarding meat intake and invasive breast cancer risk.

The Sister Study is a cohort of women in the US and Puerto Rico, who themselves have not had breast cancer but have sisters or half-sisters who were diagnosed with breast cancer. This means that this group of women will potentially have a higher risk of breast cancer themselves, which was acknowledged by the researchers.

The researchers showed that red meat consumption (beef, lamb, veal, pork and game meat) increased the risk of invasive breast cancer, while consuming poultry (chicken, turkey, ducks, goose, quail, pheasant/game birds) reduced the risk of invasive breast cancer.

The effect was particularly strong for post-menopausal invasive breast cancer. These associations they showed were regardless of other known risk factors for breast cancer. In this study there was no association shown between the way the meat was cooked and invasive breast cancer risk.

It is important to note that this sort of study (an observational or ecological study) is not able to provide a ‘cause and effect’ finding. It only provides associations (or links) between factors, in this case, there is a link between red meat and increased risk of breast cancer.

However it certainly adds to the body of research evidence that is growing, which in 2015 led the International Agency for Research on Cancer to announce that red meat consumption maybe possibly carcinogenic to humans (Group 2A).