Our society has a complicated relationship with red meat. On the one hand, there are few things more delicious than the elegant simplicity of a perfectly cooked steak. On the other, we feel like there absolutely has to be something unhealthy about a large cut of meat, dripping butter, even if you eat the blanched green beans on the side.
Also, there’s the environmental impact to consider.
Which means that every time a study comes out that shows that red meat might be bad for us, we leap on it with a delightful abandon. This week has been no different — according to news media from across the world, red meat is causing breast cancer. The only way to prevent it? Switch your steak for chicken breast!
Fortunately for the steak-lovers out there, the story isn’t quite as simple as that. Red meat might not always be good for your health — although that’s a very complicated question — but there’s probably no need to worry about it causing breast cancer just yet.
The study that is being bandied about by news everywhere was a pretty classic example of nutritional epidemiology. The researchers took a large cohort of people who had given detailed information about their food eating habits in 1998, and followed them up for more than a decade to see who got cancer. They pulled these records from the Sister Study, which looked at women who were at a high risk of breast cancer, and managed to get about 42,000 participants in total.
The researchers then split them up into groups depending on how much red meat/poultry they ate, and found that those who ate more red meat were more at risk, and those who ate more poultry were less at risk of breast cancer.
Basically, red meat was bad, while poultry was good.
This was a pretty solid piece of research — the scientists controlled for about a dozen potential confounders, which are things that can cause both the outcome of interest and the exposure (in this case cancer and red meat consumption, respectively). It was also a very large sample, and the follow-up took place over the course of more than a decade.
The researchers also conducted a more complex analysis where they tried to calculate what would happen if people replaced red meat with poultry. In this model, they found that replacing red meat with poultry was associated with a reduced risk of breast cancer. There were also some weak correlations between cooking practices — rare vs. well-done/charred meat, for example — and found that grilled red meat might be protective against cancer.
But hang onto your beef burgers, because this is where the science gets a bit murky.
Before you go running from your chicken-fried steak, there are a few things to consider about this study. Firstly, there’s the problem of residual confounding. The authors controlled for the things that they knew about — like age, income, and sex — but in this type of observational research, it’s impossible to control for everything.
We can control for the things we know about and measure, but we can’t control for what we don’t know or can’t measure.
This is a problem, because there are many things that can cause people to change their eating habits that are also risks for cancer. Maybe the people who ate more red meat were also exposed to one of the many environmental causes of breast cancer — the scientists tried to adjust for this, but there’s only so much you can do in this sort of study.
Another issue was that the cohort only had one recording of food intake, which was done in 1998. Based on this single survey, the researchers split people up into groups of meat intake. But people change their diets all the time, and there’s no guarantee that what these women were eating in 2009 was even remotely similar to their meat intake in the late 90s. This issue becomes even bigger when you remember that people regularly lie and make mistakes on surveys about food.
The absolute risk increase for eating red meat in this study was also absolutely tiny. While most news outlets only reported the relative risk increase of ~25%, which sounds terrifying, the absolute risk difference of breast cancer between women who ate the least and most red meat was around 0.01%.
To put it another way, if 1,000 people in this study decided to go from being vegetarian to eating 4 steaks a week for a decade, we’d expect to see 1 additional case of breast cancer.
Sounds a bit less scary when I put it that way, doesn’t it?
The reality is that this study didn’t prove all that much. There was a small increase in risk associated with a higher self-reported intake of red meat, but it’s very hard to know whether that’s a causal relationship — red meat causing cancer — or just an association caused by other factors.
This also isn’t the first time scientists have looked at this question — previous studies, many of them much bigger than this one, have been quite inconclusive about whether red meat itself causes breast cancer. Some show a connection, but others have not found anything of the sort. The one thing that most previous research has shown very strongly is that processed meat is associated with breast cancer risk, but ironically this new study didn’t find that at all.
Is red meat good for your health? That’s a very complicated question with more than one answer. It depends on your dietary pattern, lifestyle, and may have a lot to do with how you cook your food.
Is red meat causing breast cancer? Currently, we aren’t really sure, but even if it is the risk is probably pretty tiny. It’s the sort of risk that’s very important to public health people looking at millions, but not very meaningful to the individual sitting at home. If you’re worried about your diet, see a dietitian.
Don’t worry too much about the steak.
Chances are, it’s not giving you cancer after all.