Wednesday, April 25, 2012

The Meaty Gritty on the Red Meat Debate: A Comprehensive Rebuttal of the Constant Assault On My Beloved Steaks

Image 1: Even if you find this disgusting, I would like to invite you at least read what the outspoken carnivor in me has to tell you.
It appears to be an endless debate: Can you eat meat? May you eat meat? And even should you eat meat? I already mentioned in my post on the "Chinese meat supplement" study from last week that many of the accepted "truths" about real, unprocesed red meat are about as "true" as the hilarious statement that "going to the hospital causes pre-mature death"... After reading my friend Carl Lanore's luckily very reasonable and not overtly "ranting" blogpost on "What to say to a Vegan", a few days ago, I decided to sum up some of the research to scrutinize, which of the objections against and arguments for eating meat are actually rooted in science (I mean, my life as a meat eater could depend on it, right? ;-).

Pork rules, but is that a good thing?

If we take a look at the actual meat consumption in what is usully called the "developed world" (this is us), we find that pork is the most widely consumed form of red meat (>50% in developed countries; FAO. 2009)  - what's more, pork is rarely consumed "intact", in the form of a whole cut of meat, but more often as processed meat like sausages etc. Overall, the average available amount of red meat (pork, beef and veal, sheep) people in the developed world consume on a daily basis is ~110g, which is well within the "save limit" of as defined by the dietary recommendations in the respective countries.
Figure 1: Relative contribution of beef (total and lean) to individual nutrient consumption in the American diet (adapted from Zanovec. 2010)
In fact, a 2010 dietary analysis by Zanovec et al. suggests that with an average beef intake of 49.3g/day US adults eat way less than the recommended 142-198g of meat per day (at least if we count beef alone; Zanovec. 2010). In this context it is also worth mentioning that:

"Lean beef contributes significant amount of key nutrients to the US diet"

This statement, by the way, is taken directly from the title of Zanovec's analysis of data from the National Health and Nutrition Examination Survey (NHANES. 1999-2004). The years of dietary recommendations asking the public to avoid red meats, because their high saturated fat content would clog their arteries have obviously made a profound impact on people's perception of meat as a "dietary treat" that is about as unhealthy, if not worse, than their beloved potato chips, twinkies and dingdongs and that despite increasing evidence that saturated fat is not associated with an increased risk of heart disease, but showed a statistically non-significant association with reduced risk of stroke (-19%, p = 0.11; Siri-Tarino. 2010).

The dietary advice people are given does "not reflect available scientific literature"

In a relatively recent "review of the reviews" the purported experts on respective dietary advisory boards conduct,  Robert Hoenselaar a researcher from the Department of Nutrition and Dietetics at the High School of Arnheim and Nijmegen in the Netherlands concludes that
[t]he results and conclusions about saturated fat intake in relation to CVD, from leading advisory committees, do not reflect the available scientific literature."
and criticizes the policymakers (if applicable to a certain organization, I will name the latter in brackets after each statement) for
  • advising people to replace saturated with polyunsaturated fats in their diets based on two non-randomized trials (EFSA)
  • mentioning the existing evidence that saturated fat intake increases HDL cholesterol, but ignoring the conclusive evidence that increased HDL levels are associated with a lower CVD risk (IOM, EFSA)
  • not taking into account data from existing prospective studies examining the direct relation between saturated fat intake and CVD (USDA, IOM, EFSA) and instead including their "own randomly selected data on this subject" in their reports
  • ignoring their own previous results (USDA), which suggest that replacing saturated fats by carbohydrates or monounsaturated fats decreases the CHD risk and the mere fact that in the studies Hoenselar analyzed, none of the authors concluded that "changes in saturated fat intake would change the risk of CVD, regardless of the study design and the endpoint"
  • not discussing other modifiable dietary risk factors, which often go hand in hand with an increased meat consumption such as higher intakes of industrial trans fatty acids, a overtly high salt intake or a carbohydrate-laden high GI diet.
Any probably inevitable selection biases aside, it is also interesting that papers such as the one by Li et al., which found no increase in cholesterol (in fact a reduction in LDL) or thrombotic risk factors from the consumption of lean red meat (grass- and grain-fed) in their 2005 review of 54 pertinent studies (Li. 2005), do not appear in the extensive lists of literature the members on respective advisory boards attach to their well-worded reviews.

RCTs confirm independent reviews of the literature and well-conducted epidemiological studies

Moreover, most recent randomized controlled trials, such as Roussell et al. support the notion that the inclusion of lean red meats (153g/day) in a "heart healthy" DASH-like diet does not diminish its favorable effects on markers of cardiovascular disease (Roussell. 2012), but...
[...] in conjunction with the beneficial effects on apolipoprotein CVD risk factors after consumption of the BOLD and BOLD+ [BOLD 133g; BOLD+ 153g/day of lean beef, cf. DASH <28g/day] diets, which were greater with the BOLD+ diet, provide support for including lean beef in a heart-healthy dietary pattern.
Eating a small steak every day is thusly - according to the results from the latest randomized controlled trials more beneficial for your heart (and probably overall health, e.g. "Heal Your Thyroid by Eating More Beef") than avoiding red meat like a plague.

Don't freak out over real meat, or your blood pressure will raise; yet not from the meat!

The list of studies showing no association to another often touted "meat-related" cardiovascular risk factor, high blood pressure (the "silent killer"), is extensive, and even the 2010 U.S. Dietary Guidelines Advisory Committee recently concluded that there is
[...] no clear association between intake of animal protein products and blood pressure in prospective cohort studies.

In randomized controlled trials, as those by Hodgson et al. and Nowson et al,. the addition of red meat to a diet that was "otherwise considered heart healthy" lead to modest reductions (not increases!) in blood pressure (Hodgson. 2006; Nowson. 2009). It is thusly no wonder that in a forerunner study to the aforementioned Roussell trial a sixfold increase in real red meat intake (from DASH to BOLD, cf. above) did not lead to any statistically significant elevations in blood pressure. What is quite interesting in this context is that, at least in the Nowson trial, the dietary restriction of sodium basically precluded the intake of "regular" processed "meats" (I personally would not call them such, but scientists and most people consider sausages & co "meat").

Meat does not make you fat! It can make you lean - not skinny, though...

Another commonly touted myth that is widely accepted - especially among female mainstream dieters - is that meat will make you fat (or if not fat, then at least "bulky"). That this is not the case and chicken and fish are not per se better protein sources when you are dieting for weight loss has been shown in randomized controlled trials (Leslie. 2002; Campbell. 2010) - particularly in women, by the way. This should also remind the "regulars" among you (i.e. all of you who follow my advice to get their daily dose of SuppVersity news in order to stay sane and prolong their lives ;-) of a previous blogpost of mine, in which I discussed the results of a study by Petzke et al. from September 2011, which found increases in lean mass in weight stable women who were advised to include additional lean pork (=red meat ;-) in their diets. I have written about similar results in an obviously tighter controlled rodent study, little less than a week or two, ago.

Image 2: If you put any faith in prospective studies, you should make sure that your grand parents do not follow this selfish advise.
A 14-year prospective follow-up study of older adults by Gilsing et al. did even identify the men in the highest quintile of beef consumption (>40g/day, which is hilarious and just goes to show you why old people get sick and fragile, by the way) as those with the lowest increase in BMI (Gilsing. 2012). However (and moreover), at the end of the 14 year follow up, ...
[...], a significantly higher increase in BMI was associated with higher intakes of pork in women (BMI change highest vs. lowest quintile: 0.47 kg/m²) and chicken in both sexes (BMI change highest vs. lowest category in both men and women: 0.36 kg/m²).
To stay away from unprocessed red meats, and beef, in particular, in order to lose weight or maintain a healthy body weight, is thusly not only unnecessary, but probably even counter-indicated. Also, because red meat is one of the richest sources of protein, iron, zinc, vitamin A and other vital nutrients, all of which could be scarce on voluntary (young dieters) or involuntary (loss of appetite in the elderly) calorie reduced diets.

"Fine, but you will die from cancer, when you eat too much meat"

When the CVD and obesity debate are settled, the meat opponents usually feel that it's now time to play what they believe is their ultimate trump: The red meat "causes" cancer argument - an argument on the validity of which McNeill et al. state (McNeill. 2012):
Disentangling the independent effects of individual foods, such as red meat, in cancer etiology is a substantial challenge (Magalhaes et al., 2012). Although many epidemiologic studies have observed positive associations between red/processed meat intake or associated dietary patterns and various cancers and thus concluded that these convincingly increase cancer risk, these associations have generally been weak in magnitude and/or the large majority of associations have not been statistically significant (Chan et al., 2011; Alexander et al., 2010; Alexander et al., 2010b; Alexander et al., 2009b).  Not surprisingly, analyses of data from large prospective studies have found little or no association between fresh red meat consumption and colorectal cancer risk.
Image 3: Linda van Horn is a chair on the 2010 US Dietary Guidelines Advisory Commitee that is going back on its previous advice against all things meat.
As in the case of increased blood pressure, the 2010 US Dietary Guidelines Advisory Committee (DGAC) is thusly backpedaling on previous statements and recommendations and ascertains that the existing scientific evidence shows "no consistent findings on type of meat or meat product and colorectal cancer" and even recommends that
Americans may choose animal products as part of their diet based on the body of evidence showing a general lack of relationship between animal protein consumption and selected health outcomes (DGAC, 2010).
In view of the fact that there are still epidemiological trials, which do suggest that increased consumption of red meat could pose an increased cancer risk, it will be all the more important to try and eliminate methodological shortcomings, such as
  • heterogeneous definitions of red and processed meat (is Pizza Salami really "red meat"?),
  • variable and unreliable measures of meat consumption, and
  • profound inter-study differences in the analytical evaluation of the data
as well as confounding factors such as physical activity, body mass index, body fat levels, alcohol intake, or adherence to screening recommendations, in order to pinpoint any allegedly meat-related increases in cancer risk in the future.

The non-health related ethical dilemma

By now, I have hopefully encouraged my fellow carnivores and maybe even convinced some skeptics (you know I love you ;-) that the allegedly conclusive data on the potential health hazards from an average, let alone increased consumption of real (unprocessed) red meats are at least not conclusive, and, from my naturally biased reading of the available evidence, non-justifiable and to a great extend the result of paradigmatic ignorance towards contradictory research.

Yet whatever your take on the health effects of red meat consumption may be, now that you have reached the end of this article, it is still up to you to decide if you want or don't want to eat formerly living creatures. I have made my decision and ask you to accept mine, just as I will accept yours - whatever it may be. Thank you!