The 2009 Study Versus the 2013 Study
Before I break anything down, let's look at details of the studies.
The 2009 study, "Meat Intake and Mortality," assessed men and women with baseline ages between 50 and 71 years old for 10 years. A total of 617,119 people participated, hailing from eight states which represented different regions of the United States. The researchers put the men and women into quintiles based on their sex and frequency of red meat consumption. The results showed the rate of all-cause, cardiovascular, and cancer-related mortalities increase with the frequency of red meat consumption for men and women. The relationships were the same for death rates in men and women when connected with processed meat consumption as well.
The story painted by the 2013 study results was much different. The 2013 study is the third installment of the National Health and Nutrition Examination Survey (NHANES), a series of US population studies taking place over decades. In the NHANES study, 17,611 men and women participated. The study covered a 25-year period. The results showed no association between red meat and any of the mortality causes (all-cause, cancer, or heart disease). In fact, greater meat consumption was associated with lower body mass index and blood pressure.
The studies are, by no means, equal. Obviously the sample sizes and durations vary, as do the results. Which truly indicates the risk of heart disease you get from eating red meat?
- Both are longitudinal studies, or types of studies that can determine associations but cannot prove causation. These studies lack the control of other life factors to prove that any one factor leads to another factor. If you take the 2009 study's association of red meat with heart disease or cancer-related death to be causation, then you must also say that eating red meat helps women get married/avoid divorce: red meat consumption was strongly connected with the status of being married for women.
- The classifications were different. Red meat in the 2009 study included processed meats, such as bacon, sausage, and meat on pizza or in lasagna. The NHANES study analyzed processed meats only as their own category. In other words, a slice of pepporoni pizza would quality as a serving for the red meat and processed meat categories in one study, but only as a processed meat in the other study.
- Diets were assessed via questionnaires at the start of each study. This presents a ton of room for error. People can be inaccurate or intentionally lie when it comes to recalling what they ate. Also, there was no dietary follow-up. The study assumes participants keep their diets the same over time. I don't know about you, but my diet has drastically changed in the last five years, let alone the last 10 or 25.
The Objectives of These Studies
Correlation-finding studies such as the two discussed here serve two major purposes: to disprove a causation hypothesis or to keep a hypothesis alive so it can be studied further in causation studies. The studies aren't unanimous in showing a relationship between red meat and death from heart disease or cancer. However, they did both show reductions in some mortality risks for men with higher amounts of white meat and fish, meaning more research should be conducted to see if either can increase men's longevity.
For a number of reasons, you should not walk away from these studies believing that red meat kills people by causing heart disease or cancer. If you do, remember to tell your female friends to eat more red meat if they hope to become or stay married.