A surprising meta-analysis was published in the Annals of Internal Medicine last month stating that it’s okay to keep eating red and processed meat (1). Given the wealth of research that points out the many health benefits of reducing or eliminating meat from the diet, the conclusion of this study is puzzling to say the least. It’s time for some healthy skepticism and a deeper look into this study.
NutriRECS Working Group is the committee that authored this study. It is “an independent group with clinical, nutritional and public health content expertise, skilled in the methodology of systematic reviews and practice guidelines, who are unencumbered by institutional constraints and conflicts of interest, aiming to produce trustworthy nutritional guideline recommendations based on the values, attitudes and preferences of patients and community members” (2). It seems to me to be a perplexing concept to strive to produce trustworthy nutritional guidelines based on the preferences of patients!
There is no new research to be found in this recent meta-analysis, just previous studies re-analyzed. NutriRECS investigated the effects that reducing red and processed meat consumption might have on people’s lives and related them to the health consequences of eating meat. The result was a six-part process leading to its unexpected conclusion.
Part One: (3,4)
NutriRECS acknowledged that both recent and past studies show associations between consumption of unprocessed red meat and processed meat with increased risk for cancer, stroke and diabetes; death from cardiovascular conditions and stroke; and death from all causes. However, they felt sympathetic to the food preference of many people who choose to eat meat and undertook a review of published studies concerning the choices that people make regarding meat consumption.
Results from this review brought to light some reasons for eating meat including…
Considering meat essential to a healthy diet
Considering meat to be part of one’s culture
Uncertainty about preparing adequate and tasty meals without including meat.
Some participants in this review stated that they would be unwilling to give up meat even if they were presented with information about its potential harmful health effects.
Part Two to Five: (5,6,7,8)
Along with the Part One review, the NutriRECS Working Group looked at the evidence that already exists regarding the effects of reducing red and processed meat consumption. They searched the databases and identified all relevant studies on harms and benefits of the consumption of unprocessed red meat and processed meat. Their literature search revealed over 22,000 eligible studies but this number was pared down to less than 100 for use in this study. The following are the results of the four meta-analyses performed by the NutriRECS researchers.
NOTE THAT ALL FOUR OF THE FOLLOWING META-ANALYSES THAT WERE PART OF THIS RESEARCH SHOWED THAT REDUCING RED AND PROCESSED MEAT INTAKE RESULTED IN CLEAR AND SIGNIFICANT REDUCTIONS IN THE INCIDENCE OF AND DEATH FROM CARDIOVASCULAR DISEASE, DIABETES AND CANCER.
Part Two: (5)
A systematic review and meta-analysis of observational cohort studies to evaluate the effects of different dietary patterns, especially different amounts of red or processed meat, on all-cause mortality, cardiometabolic outcomes, and cancer incidence and mortality.
Results showed that diets low in red and processed meats were significantly associated with…
13% lower risk of death due to all-causes
14% lower risk of death due to cardiovascular disorders
14% lower risk of non-fatal stroke
24% lower risk of type-2 diabetes
10% lower risk of incidence of cancer
11% lower risk of death due to cancer
This review concluded that including less red and processed meat in the diet would lead to small reductions in cardiovascular, metabolic and cancer outcomes and rated this evidence as low to very low.
Part Three: (6)
A systematic review and meta-analysis of observational cohort studies to evaluate the association between red and processed meat consumption and all-cause mortality, cardiometabolic outcomes, quality of life, and satisfaction with diet among adults.
Results showed that …
Reducing red meat intake by 3 servings a week was significantly associated with….
7% reduction in death due to all causes
10% reduction in death due to cardiovascular disease
6% reduction in incidence of stroke
7% reduction in risk of heart attack
10% reduction in risk of type-2 diabetes
Reducing processed meat intake by 3 servings a week was significantly associated with…
8% reduction in death due to all causes
10% reduction in death due to cardiovascular disease
6% reduction in incidence of stroke
6% reduction in risk of heart attack
22% reduction in risk of type-2 diabetes
Note: 1 serving of meat in this study was approximately 120 gm
This review concluded that reductions in the consumption of red and processed meat would result in only very small reductions in death due to cardiovascular disorders, death due to all-causes and adverse heart and metabolic outcomes. This evidence was rated as of low certainty.
Part Four: (7)
A systematic review and meta-analysis of observational cohort studies to evaluate the effect of a reduction in red and processed meat intake on the incidence of cancer and death due to cancer.
Results showed that…
Reducing red meat intake by 3 servings per week was significantly associated with…
7% reduction in overall death due to cancer
Reducing processed meat intake by 3 servings a week was significantly associated with…
30% reduction in incidence of esophageal cancer
7% reduction in incidence of colorectal cancer
10% reduction in incidence of breast cancer
8% reduction in overall death from cancer
This review concluded that the effects of red and processed meat consumption on cancer mortality and incidence are very small and the certainty of this evidence is low to very low.
Part Five: (8)
A systematic review of randomized trials looking at the effect of lower versus higher red meat intake on the incidence of cardiometabolic and cancer outcomes in adults.
There were twelve eligible trials for this review, however, in the end, most of the data came from just one of them. Only two of these randomized long-term trials reported on the patient outcomes the researchers were looking for. Regrettably, neither were actually meat reduction trials. One of them, the Lyon Heart Study, was discounted by the NutriRECS researchers because they considered the results were implausibly high, its number of participants was low at 605 people and the study was discontinued early due to the large beneficial effects. (After 46 months of follow-up, subjects following a Mediterranean-style diet emphasizing fruits, vegetables, breads and cereals, and fish had a 50% to 70% lower risk of recurrent heart disease (9)). This left mainly the data from the Women’s Health Initiative which was a trial encompassing over 48,000 subjects who were following a low-fat dietary pattern. The participants were not instructed to reduce meat although some meat reduction did occur because participants were eating a lower fat diet (33).
This review concluded that diets restricting red meat have little to no effect on major cardiovascular and metabolic outcomes and cancer incidence and mortality.
However, the actual results of the Women’s Health Initiative trial showed that, after 19.6 years of follow-up, modest dietary changes including slight reductions in meat intake were significantly associated with (34)…
16% reduction in incidence of breast cancer followed by death
13% reduction in diabetes requiring insulin
Part 6: The Final Conclusion (1)
The final study gathered all the information gleaned from these five different reviews and came up with new dietary guidelines regarding the dietary intake of red and processed meat. The startling recommendation was the advice for adults to continue their current intake of unprocessed red meat and processed meat. In other words, though all the studies included in this meta-analysis found that eating red and processed meat was linked to negative health outcomes, it’s okay to keep eating meat. The researchers called this a “weak recommendation” based on the perceived low or very-low quality of evidence revealed in their studies. The rationale given was that the absolute risk reduction gleaned from decreasing meat intake was very small and, given the attachment of people to their meat-based diet, the amount of risk reduction gained by not eating meat would not be high enough to motivate people to reduce their consumption of red or processed meat.
Note that this conclusion was not unanimous among the study researchers themselves. Three panel members out of the fourteen voted against their own recommendations (2). Also, another researcher, Dr. John Sievenpiper, was a co-author of one of the meta-analyses and a nutritional epidemiology and meta-analysis expert and professor at the University of Toronto Department of Nutritional Sciences. He strongly disagreed with the conclusion stating, “Unfortunately, the leadership of the paper chose to play up the low certainty of evidence by GRADE, as opposed to the protective associations that directly support current recommendations to lower meat intake.” He went on to say, “The signals would be even stronger if one considered substitution analyses with plant protein sources or investigated dose-response gradients which are used to upgrade data by GRADE, both of which I had requested. Unfortunately, I never saw the galley proofs to ensure that these changes had been made” (2,10).
Results from these meta-analyses confirmed existing evidence that eating red and processed meat has negative health effects. How then did that verification translate into a recommendation for adults to continue to consume meat? A more accurate conclusion might have been the recommendation to create clear and understandable information regarding the negative effects on health of eating red and processed meat with aids to help make the transition to eating less meat so that consumers have a greater chance of being successful in reducing or eliminating meat intake.
Problems With This Study
The researchers viewed the quality of the evidence derived from these studies as low or very low. In this project, studies were re-analyzed using a new measurement tool called GRADE (Grading of Recommendation, Assessment, Development and Evaluation). Unfortunately, this tool was developed to evaluate pharmaceuticals and does not effectively transfer to evaluation of the effects of lifestyle factors. Other criteria have been developed for assessing the effects of diet, lifestyle and environmental factors including HEALM (Hierarchies of Evidence Applied to Lifestyle Medicine) or the criteria developed by the World Cancer Research Fund. Using one of these alternate methods would have been more appropriate and likely would have provided evidence of higher quality (2).
The findings from the studies used in this meta-analysis were heavily adjusted for factors such as cholesterol level, body weight and blood pressure. Since eating meat can be the cause of increased cholesterol levels, higher body weight and high blood pressure, adjusting for these would diminish or completely mask any harmful effects stemming from meat intake (11).
Researchers claimed that the benefits of meat reductions were very small. But their studies looked only at reducing meat by three servings a week. Research shows that well over one-third of North Americans eat more than one serving of meat every day. Larger reductions in meat intake would be expected to result in larger benefits (2).
Dietary guidelines should not be based on personal dietary preferences such as taste and reluctance to change established habits (2). The authors assumed that it is just too difficult for most people to make major changes in their eating patterns. On the contrary, lasting changes in dietary choices are occurring now at an unprecedented rate. Just look at the increase in people turning to vegan diets. The last three years have seen a 600% increase in people identifying as vegans in the US (12). UK vegans have increased by 350% over the last 10 years (13). And more than half of Canadians report that they eat meat alternatives at least a few times a week (30). Additionally, research that involves transitioning to a plant-based diet reports that adherence to such a diet remains very high even five years after the studies are completed (14).
Other major research not included in this meta-analysis
Numerous key studies were left out of this analysis. The following are a few examples.
The British Medical Journal published a study in 2017 involving more than 500,000 people that found that consuming red meat, both processed and unprocessed, increased the likelihood of dying from most major causes including cancer, heart disease, respiratory disease, stroke, diabetes, infection, kidney disease and liver disease. (15)
In the PREDIMED study of over 5,000 participants with high risk of cardiovascular disease, the replacement of red meat with healthier foods substantially reduced the risk of cardiovascular disease (16). The largest reductions in cardiovascular mortality were found in those eating a more vegetarian diet pattern (17).
The NIH (National Institutes of Health) and the AARP (American Association of Retired Persons) followed over 500,000 men and women for ten years. Meat consumption was associated with increased risk of early death from any cause as well as increased risk of dying specifically from cancer and heart disease. This study controlled for other diet and lifestyle factors such as smoking, exercising, alcohol use and actual diet content and the link between meat consumption and early death remained strong (18).
The Lifestyle Heart Trial showed that intensive lifestyle changes including a 10%-fat-vegetarian-whole-foods diet, regular exercise, stress management and smoking cessation could reverse the progression of severe atherosclerosis in the coronary artery (14).
Last but certainly not least is the group of research that prompted the World Health Organization to label red meat as “probably carcinogenic to humans (Group 2A)” and processed meat as “carcinogenic to humans (Group 1)” (32).
Lead researcher failed to declare his funding and conflicts of interest
Declarations of conflicts of interest and funding sources are required by reputable journals (31). Bradley C. Johnston, lead researcher of this study, has past ties to the meat and food industry. Mr. Johnston listed his funding for this study as “None” and stated that he was not required to report his past relationships with industry (19,20,21).
Reactions from health organizations
Dr. Walter Willett, MD, P.H., is a professor of Epidemiology and Nutrition at Harvard T.H. Chan School of Public Health. He stated, “This report has layers of flaws and is the most egregious abuse of evidence that I have ever seen.” (10)
Marco Springmann from the Oxford Martin Programme on the Future of food stated that “the recommendation that adults continue current red and processed meat consumption is based on a skewed reading and presentation of the scientific evidence… even with this skewed way of presenting the evidence, the reviews clearly indicate the benefits of reducing red and processed meat consumption.” (10)
True Health Initiative, a global coalition using science-based evidence to decrease the incidence of preventable diseases, issued a letter to the publishing magazine, Annals of Internal Medicine, recommending that they retract the publication of this paper on the basis of their “grave concerns about the potential for damage to public understanding, and public health.” This letter was signed by, among others, David L. Katz, MD, the Founding Director of Yale University Prevention Research Center; Richard Carmona, MD, MPH, FACS, the 17th Surgeon General of The United States; Christopher Gardner, PhD, of Stanford University Prevention Research Center; Frank Hu, MD, PhD, Chair of the Department of Nutrition for Harvard T.H. Chan School of Public Health; Dariush Mozaffarian, MD, Dean of Friedman School of Nutrition for Tufts University; and Kim A. Williams, MD, Chief of the Division of Cardiology for Rush Medical College and Past President of the American College of Cardiology. The magazine agreed only to slightly modify the headline in their press release but refused to retract or alter the message of this paper. (10)
The PCRM (Physicians’ Committee for Responsible Medicine) has risen to the challenge and filed a petition with the Federal Trade Commission in the US to correct the false statements concerning the consumption of red and processed meat printed in the Annals of Internal Medicine. They charge the journal with printing information directly at odds with the plentiful scientific evidence of the damaging health effects of consuming red and processed meat. They further state that the information given in the journal article promotes physical harm to those who follow it. (22)
Other protests have been registered by The Center for Science in the Public Interest, the American Institute for Cancer Research, and the Harvard T.H. Chan School of Public Health (10).
This bit of research is not necessarily the opinion of the journal that published the study. However, the Annals of Internal Medicine, a publication of the American College of Physicians that is generally well-respected, has a rather shameful history of disseminating health studies that are in direct conflict with substantial previous evidence.
In 2014 the Annals of Internal Medicine published a review that led to the infamous article in TIME magazine proclaiming to “Eat Butter” and “Ending the War on Fat”. The review discounted the health benefits of lowering consumption of saturated fats (23,24). Walter Willett, professor of Epidemiology and Nutrition at Harvard T.H. Chan School of Public Health warned that the conclusions presented in the study regarding dietary fat and heart disease contained major errors and omissions and were seriously misleading. Other health groups added to his voice and the magazine was forced to issue a retraction (25,26).
In 2016 the same journal published a review of the association between sugar intake and adverse health outcomes which concluded that “guidelines on dietary sugar do not meet criteria for trustworthy recommendations and are based on low-quality evidence”, suggesting that maybe eating sugar is not as harmful as we have been led to believe (27). Bradley C. Johnston was the senior researcher for this study also. Primary funding for the sugar study came from the Technical Committee on Dietary Carbohydrates of the North American branch of the International Life Sciences Institute (ISLI) whose members are a mixed bag of drug companies and food conglomerates including the Coca Cola Company, Pepsico, Inc., Dr. Pepper, the Hershey Company, Kelloggs and Cargill Incorporated, businesses with a vested interest in sugar use (28).
The publication of such studies in a major medical journal is irresponsible and unethical. Reports that strive to disprove healthy lifestyle choices already backed by abundant accumulated evidence are confusing to the public and health professionals alike and threaten the credibility of nutritional science. It is a fact that more than 80% of deaths worldwide result from chronic non-communicable diseases such as cardiovascular disease, diabetes, cancer, autoimmune diseases and many others, conditions which can be prevented and often cured through healthy lifestyle behaviours such as minimizing the consumption of red and processed meat (10,29).
It is to be hoped that this study does not lead to changes in current dietary recommendations. Robust research from randomized controlled trials and long-term epidemiological studies illuminate the pathway to good health through a diet high in plant-based whole foods. The agendas of big business and sensational magazine articles must not be allowed to discredit the decades of solid evidence that we have already collected about healthy eating.
1 Johnston, B.C., Zeraatkar, D., Han, M.A., Vernooij, R.W.M., Valli, C., Dib, R.E., et al. Unprocessed Red Meat and Processed Meat Consumption: Dietary Guideline Recommendations From the Nutritional Recommendations (NutriRECS) Consortium. Ann Intern Med. Oct 1, 2019. DOI: 10.7326/M19-1621
3 Valli, C., Rabassa, M., Johnston,B C. et al. Health-related values and preferences regarding meat consumption. A mixed-methods systematic review. Ann Intern Med. October 1, 2019. DOI: 10.7326/M19-1326
4 Carroll, A.E., Doherty, T.S. Meat Consumption and Health: Food for Thought. Ann Intern Med. October 1, 2019. DOI: 10.7326/M19-2620.
5 Vernooij, R.W.M., Zeraatkar,D,. Han,M.A. et al. Patterns of red and processed meat consumption and risk for cardiometabolic and cancer outcomes. A systematic review and meta-analysis of cohort studies. Ann Intern Med. October 1, 2019. DOI: 10.7326/M19-1583
6 Zeraatkar, D., Han, M.A, Guyatt, G.H. et al. Red and processed meat consumption and risk for all-cause mortality and cardiometabolic outcomes. A systematic review and meta-analysis of cohort studies. Ann Intern Med. October 1, 2019. DOI: 10.7326/M19-0655
7 Han, M,A., Zeraatkar, D., Guyatt, G.H. et al. Reduction of red and processed meat intake and cancer mortality and incidence. A systematic review and meta-analysis of cohort studies .Ann Intern Med. 1 October 1, 2019. DOI: 10.7326/M19-0699
8 Zeraatkar, D., Johnston, B.C., Bartoszko, J. et al. Effect of lower versus higher red meat intake on cardiometabolic and cancer outcomes. A systematic review of randomized trials. Ann Intern Med. October 1, 2019. DOI: 10.7326/M19-0622.
9 Kirs-Etherton, P., Eckel, R.H., Howard, B.V., St. Jeor, S., Bazzarre, T.L. The Lyon Heart Study: Benefits of a Mediterranean-Style, National Cholesterol Education Program/American Heart Association Step I Dietary Pattern on Cardiovascular Disease. Circulation. 2001; 103(13). 1823-1825.
14 Ornish, D., Scherwitz, L., Billings, J., et al. Intensive lifestyle changes for reversal of coronary heart disease Five-year follow-up of the Lifestyle Heart Trial. JAMA. 1998;280:2001-2007.
15 Kmietowicz, Z. Red meat consumption is linked to higher risk of death from most major causes. BMJ 2017; 357:j2241. doi: https://doi.org/10.1136/bmj.j2241
16 Martínez-González, M.A., Ros, E., Estruch, R. Primary prevention of cardiovascular disease with a Mediterranean diet supplemented with extra-virgin olive oil or nuts. N Engl J Med. 2018;379:1388-1389.
17 Martinez-Gonzalez, M.A., Sanchez-Tainta, A., Corella, D., et al. A provegetarian food pattern and reduction in total mortality in the Prevención con Dieta Mediterránea (PREDIMED) study. Am J Clin Nutr. 2014;100(suppl):320S-328S.
18 Rashmi, S., Cross, A.J., Graubard, B.I., Leitzmann, M.F., Schatzkin, A. Meat intake and mortality: a prospective study of over half a million people. Arch Intern Med. 2009 Mar 23; 169(6): 562–571.
21 Dyer, O. New red meat guidelines are undermined by undisclosed ties and faulty methods, say critics. BMJ. October 14, 2019; 367. doi: https://doi.org/10.1136/bmj.l6001.
23 Chowdhury, R., Warnakula, S., Kunutsor, S. Crowe, F. et al. Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk: A Systematic Review and Meta-analysis. Ann Intern Med. 2014;160(6):398-406. DOI: 10.7326/M13-1788 .
27 Erickson, J., Sadeghirad, B., Lytnyn, L., Slavin, J., Johnston, B.C. The Scientific Basis of Guideline Recommendations on Sugar Intake: A Systematic Review. Ann Intern Med. 2017;166(4):257-267. DOI:10.7326/M16-2020.
31 Johnson, C. Conflict of Interest in Scientific Publications: A Historical Review and Update. Journal of Manipulative and Physiological Therapeutics. February, 2010;33(2): 81-86.
33 Prentice, R.L., Aragaki, A.K., Van Horn, L. et al. Low-fat dietary pattern and cardiovascular disease: results from the Women’s Health Initiative randomized controlled trial. Am J Clin Nutr. 2017;106:35-43.
34 Prentice, R.L., Aragaki, A.K., Howard, B.V., et al. Low-fat dietary pattern among postmenopausal women influences long-term cancer, cardiovascular disease, and diabetes outcomes. J Nutr. 2019;149:1565-1574.