The media are hyping a report from the UN’s World Health Organization (WHO) that claims to link eating processed meat and red meat to cancer.
Scientists from WHO did a data dredge from several hundred epidemiological studies looking for associations between meat and cancer, specifically colon cancer.
Epidemiologic studies never provide a causal link. They can only provide statistical correlations. WHO is in the business of linking things to cancer and the data show red meat was correlated to just 3 extra cases of bowel cancer per 100,000 people. (Source). They could just as well have found associations between wearing brown shoe laces and cancer.
Steve Milloy, proprietor of the JunkScience blog says that “Not a single epidemiological study credibly links meat-eating with cancer.” (Source) He notes:
- A cardinal principle of epidemiology is that it is a very useful methodology when looking for linkage between high rates of rare diseases, the sort of relationship classically found, for example, in outbreaks of food poisoning.
- But epidemiology is wholly incapable of identifying low risks of relatively common diseases or conditions, such as most cancers. The reason for this is simple: the margin of error in study data due to inaccurate and incomplete data collection is typically far greater than the size of any statistical relationship that may exist or be detected.
- Accordingly, the rule of thumb in epidemiology, as famously espoused by the National Cancer Institute, is that, “In epidemiologic research, [increases in risk of less than 100 percent] are considered small and usually difficult to interpret. Such increases may be due to chance, statistical bias or effects of confounding factors that are sometimes not evident.”
- Further, just because a reported risk is greater than 100 percent, that does not necessarily indicate a cause-and-effect relationship. Such reported risks may be statistically insignificant (indicating they could have occurred by chance) or have wide margins of error (indicating flaky data). And, of course, for any statistical risk to have meaning, it must be backed up by biological plausibility.
One of WHO’s bogeymen is nitrates and nitrites in processed meat. The terms “nitrate” and “nitrite” seem to be used interchangeably. Nitrate (NO3) and nitrite (NO2) are inorganic ions that occur naturally and are part of the nitrogen cycle.
Nitrites and nitrates have been used for at least one thousand years to preserve meat. They block the growth of botulism, prevent spoilage and rancidity, and preserve the color.
Ingested nitrate (from foods and water) is converted to nitrite when it comes into contact with the bacteria in our saliva. Most is excreted in the urine.
WHO blames nitrites/nitrates in processed meat for causing cancer. Processed meat contains about 10 ppm (parts per million) nitrate/nitrite. WHO seems unconcerned with vegetables that contain ten to 100 times the amount of nitrate. The European Food Safety Authority (EFSA) tested the nitrate content of vegetables and reported results in their journal in June, 2008. [Note they report results as mg/kg which is the same as ppm.] Here are some examples of the nitrate content of vegetables: arugula 4,677 ppm, basil 2,292 ppm, butterhead lettuce 2,026 ppm, beets 1,279 ppm, celery 1,103 ppm, spinach 1,066 ppm, pumpkin 874 ppm.
Epidemiological studies from WHO should be taken with a grain of salt. Oh, wait, salt’s bad too.