The research is published in the journal PLoS Medicine and is the work of Amanda Cross and colleagues at the US National Cancer Institute.
Studies on the link between red and processed meat consumption and specific types of cancer have already been done, but the authors said they wanted to explore the link between red and processed meat and a number of malignancy types.
The researchers used data from the National Institutes of Health (NIH) AARP (used to be the American Association for Retired Persons) Diet and Health Study. This has a total of half a million participants aged from 50 to 71 when they were enrolled between 1995 and 1996. When they enrolled the participants filled in a food frequency questionnaire about their diet, including how much meat they consumed, how often, and of what type.
The researchers used a statistical method called Cox proportional hazards regression to find links between meat consumption patterns and cancer outcomes.
The results were analysed in quintiles (fifths) of red and processed meat intake, that is for each of the two categories of meat, each participant was put into one of five groups, depending on their intake. The participants who ate the most were in the top 20 per cent or quintile, and the ones who ate the least were in the bottom 20 per cent or quintile.
The results showed that:
- During up to 8.2 years of follow up, there were 53,396 cancer incidents in the overall cohort.
- For read meat intake, the 20 per cent of participants who ate the most, showed statistically significant higher risks for esophageal, colorectal, liver, and lung cancer, compared to the 20 per cent who ate the least.
- The risks ranged from 20 to 60 per cent higher, depending on the type of cancer.
- For processed meat consumption, the 20 per cent of participants who ate the most, showed a 20 per cent higher risk for colorectal cancer, and a 16 per cent higher risk of lung cancer, compared to the 20 per cent who ate the least.
"Both red and processed meat intakes were positively associated with cancers of the colorectum and lung; furthermore, red meat intake was associated with an elevated risk for cancers of the esophagus and liver."
The researchers took into account potential confounding factors such as smoking status, but admit other lifestyle factors may have influenced the results.
Also, there was a degree of overlap in the definitions of red and processed meat. For example, bacon and ham were included in both definitions. So it is not possible to say for certain which of the two types of meat is linked to which type of cancer.
Another limitation of the study was that most of the participants were non-Hispanic whites, so the findings may not apply equally to people with other genetic backgrounds.
However, the authors are confident that their findings strongly suggest reducing consumption of red and processed meat reduces overall cancer incidence.
In another article in the same issue of the journal, Anita Koushik (Department of Social and Preventative Medicine, University of Montreal, Canada) and Jeanine Genkinger (Department of Oncology, Division of Cancer Genetics and Epidemiology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington), reviewed the study and other key research on the links between meat intake and cancer.
They stressed that the strongest risk factors for cancer among Americans are smoking and obesity, but conceded that understanding the complexity of how diet, smoking and obesity interact, and how specific foods and nutrients are processed through the body's metabolism, could shed light on the development and perhaps even more importantly, the prevention of cancer.
They concluded that red and processed meat consumption "appears to be positively associated with risk of cancer of the colon and rectum, esophagus, liver, lung, and pancreas in a new, large US cohort study of 500,000 men and women". But the study yielded little support for a link with other types of cancer.
They referred to current dietary guidelines that recommended consuming meat that was lean, low or free of fat, thus promoting limited red and processed meat consumption. The guidelines they referred to were the Dietary Guidelines for Americans (2005), produced by the US Department of Health and Human Services and the US Department of Agriculture.
"A Prospective Study of Red and Processed Meat Intake in Relation to Cancer Risk."
Cross AJ, Leitzmann MF, Gail MH, Hollenbeck AR, Schatzkin A, et al.
PLoS Medicine Vol. 4, No. 12, e325
Click here for Article.
Click here for Koushik and Genkinger article.
Click here for Dietary Guidelines for Americans (2005).