Meat and Cancer: Not Guilty.

The Union of Concerned Scientists from Johns Hopkins University was the likely little bird that suggested…er, claimed... a relationship between red meat and cancer. Let’s give their statement a little context first about how scientific promulgations are transmitted to mainstream society.

Say this news headline appeared in the paper: Norway at peace for the 66^th consecutive year. Would you frantically rush to grab yourself a copy?

Imagine a world conference on nutrition and health has been called by scientists studying several different foods as risk factors for cancer. The agenda might look something like this:

• ·         No relative risk shown from consumption of conventional vs. organic orange juice
• ·         No effect of turkey vs. chicken consumption on cancer cell development
• ·         Does consuming expeller-pressed rather than extracted canola oil increase risk for cancer? (No)

…you stop reading the agenda here because you begin to suffer a severe case of boredom.

We all know that good news is no news. Publication bias, when something is less likely to be published if it is inconclusive or simply affirms the status quo, exists in the science world just as it does in journalism. Have you seen this message in fine print, usually following an asterisk on a milk carton: "FDA states: No significant difference in milk from cows treated with artificial growth hormones.”  However, it’s a lot more exciting as a consumer to buy milk that’s labeled “rBST Free!” “Milk from cattle not receiving artificial hormones!”…and we assume from these messages that rBST is guilty of making our milk less healthy, while ignoring the FDA’s dry statement (which deserves its own exclamation point!).

As we return to today’s topic of red meat and cancer, keep in mind that scientists hardly know what causes cancer, or even how it is caused. Several carcinogens are known to be found at the crime scene, but the direct culprits are often mysterious. I have seven meta-analytical studies (which compile data from dozens to hundreds of studies to make more powerful, broader claims since the sample populations are bigger) and, to spoil their ending for you, they all are either inconclusive or conclude with no association between red meat and cancer.

That’s good news for me, since my mother had breast cancer and I still get to enjoy all the beef and lamb I like. If you’re still curious and want to read the summaries of these studies, by all means, continue!
 

Alexander et al., 2010 “A review and meta-analysis of red and processed meat consumption and breast cancer”

A meta-analysis that examined over 25,000 cases of breast cancer compared cohorts of high red or processed meat consumption with cohorts of low red or processed meat.  It was found that “no association was observed in the fixed-effects meta-analysis of processed meat intake and breast cancer” and “No significant association between the highest category of red meat intake compared with the lowest category of intake and breast cancer was observed”. Many hypotheses such as cooked and overcooked meat by-products (heterocyclic amines, polycyclic aromatic hydrocarbons), haem Fe from blood consumption, or hormones from eating meat (mammary glands have very sensitive hormone receptors) course through the halls of academia, but significant evidence to prove them has not been garnered in experimentation—if it has, the opposite has been demonstrated within an equal amount of other studies. For more information on heterocyclic amines, see the Addendum at bottom. 

Alexander et al., 2010 “A review and meta-analysis of prospective studies of red and processed meat intake and prostate cancer”

Fifteen studies of red meat and eleven studies of processed meat were analyzed to result in a lack of supportive evidence for a correlation between dietary increments of red meat or processed meat and prostate cancer. The idea that the more meat eaten, the more at risk the person was for cancer, was not supported by the results. Circulating hypotheses for an increased incidence of prostate cancer include higher fat intake in the diet, but this also remains unproven in several studies that have taken place. In fact, high lycopene (from red pigment in fruits and vegetables such as tomatoes) and selenium (from meat) intake may reduce the risk of prostate cancer…so pour that ketchup on your burgers, people!

Alexander and Cushing, 2010 “Red meat and colorectal cancer: a critical summary of prospective epidemiologic studies”

This paper reviewed studies of European cohorts and Asian cohorts, and found no evidence that independently connected red meat to colon or rectal cancer. Red meat can’t be isolated as a cause especially because many competing factors that obscure the causes of cancer exist in the general Western lifestyle: the diet, to name one potential factor besides activity level and others, is typically high in refined sugars, starches, and alcohol, and low in fruits, vegetables, soluble and insoluble fiber.  It was found that men are 10 – 30% more likely to contract colorectal cancer than women are, but it was found to have nothing to do with men consuming more red meat than women do. In fact, a few recent studies demonstrate that red meat fats like conjugated linoleic acid (CLA) and stearic acid (an 18 carbon saturated fatty acid) are anti-carcinogenic, but further studies need to be conducted in order to continue isolating these factors for their cancer-preventative benefits (Bhattacharya et al., 2006; Evans et al., 2009; Evans et al., 2009).

Alexander et al., 2010 “Processed meat and colorectal cancer: a quantitative review of prospective epidemiologic studies”

Salt, sugar, nitrates, nitrites, phosphate, and spices are all used to cure meat and preserve them against contamination by pathogens. Smoke from wood or liquid smoke flavorings may introduce polycyclic aromatic hydrocarbons as mentioned above in the other Alexander et al., 2010 article, but nitrates and nitrites remain the largest concern, since they have shown to produce cancer in some laboratory animal studies. As mentioned in the July post “Doubtful Dining”, vegetables contain the highest concentrations of all nitrate food sources, next to some cheeses, beers, and whiskeys. The results of this study were similar to the above study regarding red meat, where the isolated variable of red meat could not be associated with colorectal cancer. Again, men were found to be about 30% more likely than women to develop the cancer, regardless of processed meat inclusion in the diet.

Alexander and Cushing, 2009 “Quantitative assessment of red meat or processed meat consumption and kidney cancer”

Again, processed meat and red meat were not shown to be risk factors for kidney cancer; however, obesity and smoking were significant risk factors.

Alexander et al., 2009 “Meta-analysis of animal fat or animal protein intake and colorectal cancer”

Over 1,000 cases of colorectal cancer were analyzed in this study. When comparing high animal fat (more than 50g) daily intake and low animal fat (less than 25g) intake on cancer risk, neither group significantly differed in their relative risk. The same inconclusive result was found for increased increments of fat (~10g increments) and for incremental percentages of energy coming from animal fats. It should be pointed out that the study did not specify the source of the animal fat or what percentages were saturated and unsaturated. If saturated fat from animals were tested, the results would be confounded between whether the fact that It was saturated OR from an animal was the problem. The study included fats from mammals, birds, and fishes. Interestingly, a systematic review from 2005 could not produce consistent evidence for Omega 3’s to reduce colorectal cancer (Maclean et al., 2006).

Alexander et al., 2010 “Summary and meta-analysis of prospective studies of animal fat intake and breast cancer”

It was found that women are more likely to develop breast cancer than men (….still paying attention? Just checking). This study compiled results from 8 other studies on 200 – 7,000 breast cancer cases. It reported that once differences in demographic, ethnic, lifestyle, and diet factors were held even, animal fats did not impact the risk for developing cancer. Perhaps saturated fats or unsaturated fats could still be involved in cancer development, but it is clear that an animal source is no different than a vegetarian source.

I have an Addendum about carcinogenic compounds in overcooked meats...

When pan-fried, smoked, or flame-cooked, meats can form heterocyclic amines which are a known to be carcinogenic. Read more about it on cancer.gov ‘s webpage. Two sentences of note to me were “the doses of HCAs and PAHs used in these studies [observing cancerous growth in lab rats] were very high—equivalent to thousands of times the doses that a person would consume in a normal diet.” and “Population studies have not established a definitive link between HCA and PAH exposure from cooked meats and cancer in humans” (only a correlation has been established).

What do you Think?