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| Dr. T. Colin Campbell |
Dr. Rodriguez’s opposing view raises considerable concerns as her statements are compromised by a number of serious methodological issues and relies largely on inaccurate stereotypes, stereotypes scripted and promoted by lobbying efforts of the livestock industry that promote fear of removing animal products from the diet.
Laboratory Experiments and the Promotion of Cancer
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| Dr. Nancy Rodriguez |
It is well documented that dietary restriction of methionine significantly increases both the mean and maximum lifespan in the rodent model.2 3 Dietary restriction of methionine has also been shown to inhibit and even reverse human tumor growth in animal models and in culture demonstrating that tumors are methionine dependent, yet is relatively well tolerated by normal tissue.4
Compared to whole plant foods, both methionine content and bioavailability is significantly higher in most protein rich animal based foods, with little overlap.3 In addition plant foods contain thousands of phytonutrients which work together to protect against cancer. For example, studies have found that casein is still far more cancer promoting compared to soy protein even when both the diets were formulated to contain equivalent amounts methionine (Fig. 1). This was attributed largely to the difference in content of a number of protective phytonutrients.5
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| Figure 1. Total number (A) and total weight (B) of mammory tumors in rats, 25 weeks after N-nitrosomethylurea injection. Diet Groups: Casein, 20% casein; SPI, 19% soy protein isolate; SPI +Met., 19% soy protein isolate formulated to contain the equivalent amount of methionine as the casein group. |
Due to the high content and bioavailability of methionine and lack of phytonutrients in other animal proteins, the observed cancer promoting effects of casein will therefore largely apply to other animal proteins. Furthermore, Dr. Rodriguez’s statement 'Casein is one of many proteins found in milk' made in an apparent attempt to disassociate milk protein from casein can be considered misleading when taking into account that casein makes up approximately 80% of the protein in bovine milk.6
Findings from Clinical Trials
The consensus that a number of dangerous substances including cigarette smoke promote cancer is purely based off epidemiologic, metabolic and laboratory studies. Therefore there is little justification for Dr. Rodriguez to claim as she did that a number of risk factors that have not been tested in clinical trials such as smoking play a significant role in the cause of cancer, but at the same time neglect evidence regarding replacing meat and dairy with whole plant foods and a decreased risk of cancer purely because of a lack of clinical trials.
A number of randomized controlled trials have actually demonstrated the damaging effects of animal protein in human cancers. For example, a randomized, placebo-controlled trial found that among men at high risk, those supplementing with milk protein were more than six times likely to develop prostate cancer compared to men supplementing with soy protein.7
A number of tightly controlled feeding trials with human participants have established that heme iron from the protein portion of meat increases the production of NOCs (N-nitroso compounds) in the digestive tract to concentrations similar to that found in cigarette smoke, of which most are cancerous.8 Furthermore, a controlled feeding trial found that NOCs arising from heme iron in meat forms DNA adducts in the human digestive tract, and DNA adducts are a well-established marker of cancer.9 These findings are consistent with recent meta-analyses of prospective studies that found that intake of both fresh red meat and heme from meat is associated with a significant increased risk of colorectal cancer.8 10
Based partly on these lines of evidence, in 2011 the expert panel from the World Cancer Research Fund reviewed over 1,000 publications on colorectal cancer and concluded that there is convincing evidence that both fresh and processed red meats are a cause of colorectal cancer.11 Furthermore, a more recent prospective study with over 2.24 million men and women found that compared to participants who consumed less than 1 serving per week, consuming 2 or more servings of meat significantly increased the risk of colorectal cancer.12
There is much controversy regarding the 'Dozens of randomized, controlled, clinical trials' that Dr. Roriguez’s appears to be referring to claiming that 'demonstrated that calcium and dairy products contribute to stronger bones'. For example the Harvard School of Public Health have asserted that:13
...the maximum-calcium-retention studies are short term and therefore have important limitations. To detect how the body adapts to different calcium intakes over a long period of time—and to get the big picture of overall bone strength—requires studies of longer duration.
Walter Willett, the Chair of the Department of Nutrition, Harvard is well known for criticizing the industries unfounded claims about the health properties of dairy. In regards to the 2010 USDA Dietary Guidelines he stated that:14
The guidelines continue to recommend three daily servings of dairy products, despite a lack of evidence that dairy intake protects against bone fractures and probable or possible links to prostate and ovarian cancers.
Willett nevertheless praised parts of the guidelines, stating that:
The guidelines appropriately emphasize eating more vegetables, beans, fruits, whole grains, and nuts and highlight healthful plant-based eating patterns, including vegetarian and vegan diets.
Dr. Rodriguez suggested that 'The Dietary Guidelines are founded on evidence-based, peer-reviewed scientific literature, and take into account the entire body of research, not just a single study', and that therefore her dietary recommendations are justified. However, evidence to the contrary was made clear in the report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2010 that stated 'The DGAC did not evaluate the components of processed meats that are associated with increased risk of colorectal cancer and cardiovascular disease.'15 Thus the Dietary Guidelines did not sufficiently 'take into account the entire body of research', one of the reasons the guidelines have been scrutinized by the Harvard School of Public Health.13
Nutrient Density of Plant vs. Animal Foods
In regards to 'calorie efficiency', the most nutrient dense foods are dark green leafy vegetables which are leaps and bounds more nutrient dense than the phytonutrient and dietary deficient animal foods Dr. Rodriguez advocates, while also being dense in protein, calcium, iron and zinc.16 In fact, calcium from a number of dark green leafy vegetables is actually much more easily absorbed than that from bovine milk.17 In regards to protein intake, a meta-analysis of nitrogen balance studies found that the estimated requirements in healthy adults for the median and 97.5th percentile are 0.65 and 0.83 grams of protein per kg of body weight respectively,18 amounts easily obtained from plant-based dietary plans formulated by Dr. Campbell and his colleagues.19 Furthermore, there is little justification for Dr. Rodriguez as she has done to advocate dairy on the basis that it is artificially fortified with Vitamin D while at the same time downplaying the nutrient density of plant-based foods due to a lack of certain nutrients such as Vitamin B12 and Vitamin D that can be easily supplemented in plant-based diets.
In regards to lean animal protein, the 95% lean beef that Dr. Rodriguez promotes actually contains a similar amount of dietary cholesterol as that found in similar cuts of full-fat beef.16 Experiments on non-human primates have demonstrated that intake of even small amounts of dietary cholesterol as low as 43µg/kcal, the equivalent found in only half of a small egg in a human diet of 2,000 kcal induces atherosclerotic lesions. Furthermore, there was no evidence of a threshold for dietary cholesterol with respect to an adverse effect on arteries (Figs. 2, 3).20 21 Furthermore, several major prospective studies on humans found that dietary cholesterol was associated with a significant increased risk of all-cause mortality.22 23 24
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| Figure 2. Subclavian artery from a Rhesus monkey supplementing 43µg/kcal dietary cholesterol. Sudanophilia (black area) is intense in the area of major intimal thickening. |
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| Figure 3. Fermoral artery from a Rhesus monkey supplementing 43µg/kcal dietary cholesterol. Intimal fibrous thickening and disruption of internal elastic membrane differentiate this artery from control vessels of monkeys supplementing 0 dietary cholesterol. |
Conflicts of Interest
Finally, Dr. Rodriguez’s financial tie to the livestock industry may explain why she appears to have misinterpreted the medical literature in regards to the disease promoting effects of animal foods and the nutrient density of plant-based foods, written in a largely textbook manner used by other livestock industry lobbyists. The tactics of the livestock industry may resemble those used by the tobacco industry that misinterpreted the medical literature in the past in order to dismiss the 'junk' science linking smoking to lung cancer and other associated diseases. Brownell et al. reminds us of how serious and real conflicts of interests can really be:25
A striking event occurred in 1994 when the CEOs of every major tobacco company in America stood before Congress and, under oath, denied believing that smoking caused lung cancer and that nicotine was addictive, despite countless studies (some by their own scientists) showing the opposite.
Perhaps the same can be said for Dr. Rodriguez’s claim that 'It is simply untrue to suggest that animal protein causes cancer', which is clearly in discordance with the preponderance of evidence. It maybe largely explained by socioeconomic factors as to why health authorities are unable to reach similar dietary recommendations as Dr. Campbell and his colleagues. For example, Eric Rimm from the Department of Nutrition, Harvard said to Reuters in regards to a major health report produced by the National Academy of Science, which he was an author of that:
We can’t tell people to stop eating all meat and all dairy produces. Well, we could tell people to become vegetarians... If we were truly basing this on science we would, but it is a bit extreme.
As Dr. Rodiguesz’s herself stated, 'appreciating the science behind nutrition helps us make smart choices about the best way to feed ourselves and the world'. Unfortunately her scare tactics illustrated in The Wall Street Journal demonstrated very little appreciation of the preponderance of scientific evidence.
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