A group of prominent researchers from Harvard University has recently weighed in on the issue of the health effects of eating red and processed meat. To date, dietary guidelines issued by many countries and health-oriented associations recommend lowering consumption of red and processed meats for optimal health. However, in late 2019, an analysis from a research group called the Nutritional Recommendations (NutriRECS) consortium muddied the waters, concluding that people should be encouraged to continue their current meat consumption habits citing “low certainty” of evidence to reduce consumption of these foods (1). (For details on the NutriRECS analysis, you can refer to my blog entitled, “True or False: It’s Okay to Eat Red and Processed Meat” published on this website on November 22, 2019.)
The Harvard-based group is made up of leaders in the fields of nutrition, epidemiology, endocrinology, medicine and population health who have authored combined research totaling hundreds of papers focusing on dietary and lifestyle determinants of health. They published a paper in the February 2020 edition of the journal, Diabetes Care, in which they discuss the NutriRECS research and conclude the following. “To improve human and planetary health, dietary guidelines should continue to emphasize dietary patterns low in red and processed meats and high in minimally processed plant foods such as fruits and vegetables, whole grains, nuts, and legumes.”(2).
Problems with the NutriRECS study identified by the Harvard researchers;
1 The GRADE system (Grading of Recommendation, Assessment, Development and Evaluation) used in the NutriRECS study to evaluate nutritional evidence has severe limitations for this type of research. GRADE was designed to evaluate the effect of one variable, such as a single drug, on a specific endpoint (33). Nutritional research is quite a different kettle of fish. Whole foods contain thousands of elements. For example, one single vegetable is a complex structure consisting of the myriad of macronutrients and micronutrients it contains within its fibrous framework. The type and amounts of each of these nutrients depend upon many variables, such as the species of the plant, the health of the soil it was grown in, the growing conditions it encountered, and its condition when harvested. Each piece of whole food is an entity unto itself and a diet is made up of thousands of these unique structures.
A mixture of observational epidemiologic investigations and randomized controlled trials (RCTs) is considered the best way to evaluate nutritional interventions. By utilizing both research methods, insights into the prevention of chronic diseases can be elucidated and causation can be determined (3). The NutriRECS research, using GRADE, branded all the observational studies considered in their analysis to be of “low quality”, negating any links to health that this research had uncovered.
2 The foods used to replace meat in the nutritional studies considered by NutriRECS were not identified or considered in their analysis. The characteristics of the replacement food used is necessary to establish a consistent pattern of benefit or non-benefit. Inevitably, substituting meat with refined carbohydrates or foods high in saturated fats will have a much different effect on health than the replacement of meat with plant-based proteins. Inexplicably, the researchers did acknowledge that Mediterranean-style diets, the DASH (Dietary Approaches to Stop Hypertension) diet and some eating patterns related to dietary guidelines were “consistently associated with positive health outcomes” although this aspect did not make it to their final conclusions (4).
3 Some robust research was excluded from the NutriRECS paper because it was considered to have too many variables. Factors such as ethnic differences in study populations (for example, Western vs Asian subjects); differing baseline diets; and variations in the replacement foods (refined carbohydrates vs other animal-based proteins vs plant-based proteins) were deemed too diverse to quantify. Contrarily, such variations need to be more deeply examined, not just thrown out or ignored.
4 The NutriRECS research showed poor selection of trials. Some of the chosen research was not designed to interpret the health effects of the consumption of red or processed meats. For instance, the Women’s Health Initiative (WHI) research was used to support their conclusion that reductions in meat ingested did not affect the risk of cardiovascular disease or cancer. This was not true at all. The randomized dietary intervention in WHI was a low-fat diet, not a reduction in red or processed meats. In the WHI trial, the overall difference in meat consumption was very small (1.4 fewer servings per week at 3 years of follow-up) (5). In addition, adherence to the low-fat diet intervention lessened over the study time.
On the other hand, trials were left out that should have been included in the NutriRECS review.
For instance, the following studies demonstrating clear reduction of cardiovascular risk when consumption of red or processed meat is reduced were not included;
A. The Lyon Diet Heart Study which observed that a diet rich in alpha-linolenic acid (high intake of fruits, vegetables, legumes and grains with moderate intake of fish and low intake of dairy and red and processed meats) was highly protective to the cardiovascular system (6).
B. A meta-analysis of eight randomized controlled trials that looked at the replacement of saturated fat, found in the diet predominantly in meat and high-fat dairy products, with polyunsaturated fat, and found a 10% reduction in coronary heart disease risk for each 5% of energy from saturated fats replaced by polyunsaturated fats (7).
5 NutriRECS studied the taste preferences of participants and considered this factor as important in the development of dietary guidelines. They reviewed a series of studies that had included food preferences in their examinations. There was no attempt to consider the reliability or validity of these studies even though the GRADE system indicated that they contained high degrees of bias and methodological problems. The NutriRECS researchers noted that many people enjoyed eating meat, considered it a part of their culture and were unwilling to stop eating it (8). Conversely, many investigations involving transitioning to a plant-based diet report that adherence to meatless diets is high and remains so even five years after the studies have been completed (9). Whether people like to eat a specific food or not, there is no place for personal taste preferences in developing dietary guidelines for health.
6 The NutriRECS authors declared that the scope of their research would not include an assessment of the environmental impacts of red and processed meat. This is a major omission and a missed opportunity to improve health in the population of the earth, given the interrelationships between the vitality of the planet and human health. The production of red meat is responsible for multiple environmental influences such as rising ambient temperatures and climate change; increasing air pollution; and increases in extreme weather events (10,11). There is also abundant evidence of the environmental benefits of increasing plant-based protein sources and reducing animal-based protein sources such as red and processed meats (12).
Potential Bias: An Additional Problem with the NutriRECS Study:
Declarations of conflicts of interest and funding sources are required by reputable journals (13). Bradley C. Johnston, lead researcher of the NutriRECS 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 (14,15,16).
Nutritional research can be contentious. The observational data used to examine nutritional effects produce associations but cannot prove causation. In cases where the data are not clear, personal opinions and conflicts of interest can influence the research and its conclusions. At the very least, results can be “spun” to influence the interpretation of the reader. Honest declarations of conflicts of interest in research are important to help identify potential bias (17).
Should Dietary Guidelines Stop Restricting Red and Processed Meats?
The research group from Harvard University answers with a definite no! They note that the recommendations from the NutriRECS consortium are based on poorly designed studies and widespread misinterpretations of evidence. Unfortunately, the NutriRECS conclusions are not justified by current evidence and yet they were published and have caused confusion for both health professionals and the general public alike.
In fact, the scientific community has already provided decades worth of well-designed trials, both interventional RCTs and observational studies, providing overwhelming evidence that high intake of whole carbohydrate foods (starchy and non-starchy vegetables, fruits, legumes and whole grains) increase longevity and decrease the risks of many chronic conditions including cardiovascular disease, type-2 diabetes, cancer and others (18,19,20,21,22,23,24,25,26). In addition, there is a vast body of epidemiological data showing that consuming red and processed meat is consistently associated with increased risk of type-2 diabetes, cardiovascular disease and cancer (27,28,29). Replacement of red meat with plant protein sources in short-term RCTs results in major health benefits such as reducing the risk of death from cancer; reduction in LDL-cholesterol and cardiovascular mortality; and the reduction of other cardiometabolic risk factors (30,31,32).
In the conclusion of the Harvard paper, the authors state that dietary guidelines for the prevention and management of chronic diseases should “emphasize dietary patterns high in minimally processed fruits and vegetables, whole grains, nuts, and legumes, while limiting red and processed meats, refined carbohydrates, saturated fats, and sugar-sweetened beverages.” (2)
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2 Qian, F., Riddle, M.C., Wylie-Rosett, J., Hu, F.B. Red and processed meats and health risks: How strong is the evidence? Diabetes Care. 2020; 43: 265–271.
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