Part 3: Non-communicable disease risk associated with red and processed meat consumption—magnitude, certainty, and contextuality of risk

"...When meat consumption is part of healthy dietary patterns, harmful associations in the statistical analysis tend to disappear, suggesting that the risk is more likely to be contingent on the dietary context rather than the meat itself..." - Johnston et al.

In mid-April 2023 several peer-reviewed papers were published in the Oxford University Press’ Animal Frontiers journal. This was put together following the October 2022 International Summit on the Societal Role of Meat. This special edition of Animal Frontiers was published by guest editors and authors, among the nearly 1,000 signatories of the Dublin Declaration warning that livestock systems are too precious to society to become the "victim of simplification and reductionism."

Following the initial meta-analysis in Part 2 on meat’s role in human nutrition, the next article looks at the research on the heavily reported links between red meat and processed meats with non-communicable disease risk. Despite meat’s role as a fundamental part of human evolutionary development, red meat, and processed meat consumption is becoming increasingly discouraged by a vocal group of scientists and organizations.

Key issues that need to be addressed when evaluating the safety of processed meats and red meat consumption:

1. What are the methods and limitations of epidemiological research;
2. How can we evaluate the certainty of the underpinning evidence;
3. What can be inferred from the current data with respect to safe or optimal intake levels;
4. What is the role of exposure in the framework of risk assessment; and
5. How can we arrive at a trustworthy message, by contextualizing these findings and relating them to the various benefits of meat products?

Methods and Limitations of Nutritional Epidemiology

• There are two main things to look out for when interpreting scientific study results - ?understanding both absolute and relative risks and understanding the research methodologies and corresponding certainty levels.
• On risks, care is needed - relative risks can be misleading. For example, a 50% relative risk reduction can be misleading if the absolute risk is going from a 2% to 1% risk difference. Absolute risks can also be misleading as results are an average across entire populations – for patients with high or low baseline risks the average risk profile is also under or over-estimating risks for that individual.
• Depending on the research methodology, the certainty around conclusions is highly variable. The gold standard is randomized trials which can result in high certainty levels. At the other end of the spectrum are observational studies, such as in the field of epidemiology, which are often limited to working outside a controlled setting, rely largely on self-reporting, and are at a high risk of confounding results, even after adjusting for variables. The current standard used across a wide range of scientific disciplines is called GRADE, which would place observational studies at a low or very low level of certainty.
• The challenge around nutrition is a research methodology that would result in high or moderate certainty is virtually impossible due to cost, timelines, and complexity. As a result, the most vocal nutritional epidemiologists claim an exception should be made for nutritional science to accept low-certainty evidence (as in the Nutrigrade or HEALM system). ?Calls to adopt less robust science should be rejected.
• One example that helps illustrate this issue is found later in the paper when looking at the data on North American meat consumption. Typically, North American studies that report subjects who consume higher levels of meat were also more likely to be current smokers, to have lower education and physical activity levels, a higher body mass index and daily intake of energy, and lower fruit vegetable and fiber intakes – hence confounding by these factors is very possible. Surprisingly, no study to date has adjusted for ultra-processed food intake, despite ultra-processed foods accounting for >50% of the calories of North Americans.

What do the large summary studies say concerning the risks and optimal intakes of red and processed meats?

• A 2019 consortium reviewed all relevant randomized trials and cohort studies and found only low to very-low certainty evidence that diets substantially lower in either red meat or processed meats reduced health risks in important health outcomes. As a result the weak recommendation from this panel was that most “adults should continue their red meat and processed meat consumption.”
• Despite this recommendation other recent publications strongly advocate a dramatic reduction or exclusion of red or processed meats:

1. In a 2019 study, the Eat Lancet Commission recommended a maximum combined intake of only 14 g/day or 100 g/week.
2. A couple of papers published in 2020 and 2021 cite earlier studies that claim 900,000 annual deaths caused by unprocessed red meat.
3. A 2021 study claims that eating one serving of a frankfurter will result in 35 minutes of life lost.
4. A 2022 paper (incorrectly) claimed consuming 100g/d and 50 g/day of unprocessed red meat and processed meats, respectfully, when compared to a diet free of these products, would reduce life expectancy for women by three years and by four years for men.

• ?These dramatic studies tend to depend on two key assumptions. First, that any consumption of red meat or processed meat is harmful, and additionally, that risk rises sharply with even moderate consumption. These assumptions do not appear consistent with the results of large epidemiology studies on this topic. Since the publication of these studies, there has been some clarification from at least one of the authors that these assumptions were not correct. Collaborators on one of the main studies have since concluded the evidence for increased risk of disease or mortality was weak, and certainly insufficient to make strong or conclusive recommendations.
• Mean global intakes per person of red and processed meats are 51 and 17 g/day respectively. Consumption is lowest in South Asia (7 and 3 g/d) and highest in Central Europe/Asia (114 and 54 g/day).?USA and Western Europe are in between at 45 and 30 g/day).
• The current evidence suggests there is no risk for consuming 75 g/day of red meats and 20 g/day of processed meats. Even beyond these intake levels, there are only small increases in relative risk reported (<25%) and little to no effect on absolute risk. The certainty of this evidence remains low to very-low based on the best available summary evidence.

Contextuality and Risk Assessment

• Red and processed meats are integral parts of many diets across the world and are typically consumed together with other foods. As a result, digestion and effects on metabolism are affected by the entire meal and diet matrix.
• One may wonder if it is appropriate to conduct a disease risk assessment of a single food product. Instead, the suggestion is that nutritional observational studies should focus on dietary patterns, albeit even if defining these patterns is also challenging.
• When meat consumption is part of healthy dietary patterns, harmful associations tend to disappear, suggesting that risk is more likely to be contingent on the dietary context rather than the meat itself. ?
• Based on contextuality, dietary recommendations should focus on healthy meal patterns tailored to individual needs, rather than specific foods, while noting that red meat (and food derived from meat) is a good source of (micro)nutrients that are not always readily available in other products, like plant-based foods.?
• Regrettably, the scientific discussion on the potential associations between meat and noncommunicable diseases is often no longer a transparent assessment of the evidence but is affected by agendas, including vested interests and ideologies.

Author's takeaways: A couple days ago Meatingplace, an industry news publication, had two relevant headlines in their morning edition. The first was “Americans stick with meat: poll” while the second read “Coalition pens letter to IPCC about meat industry’s impact on climate”.

The poll results showed strong support of meat with 76% either strongly agreeing or agreeing that it is healthy to eat meat. 17% neither agreed or disagreed, while only 4% disagreed and 1% strongly disagreed. On the topic of environment, 34% believe eating less red meat would help reduce carbon emissions. ?40% did not believe it would help and 26% remain unsure.

The other article summarized a letter sent to the United Nations Intergovernmental Panel on Climate Change (IPCC) by 98 signatories concerned that language about reducing red meat consumption was excluded from the latest report. The group is concerned with meat industry lobby efforts in a similar vein that energy companies should not have a view or role to play in providing input into energy regulations.

I feel that excluding some of the largest stakeholders in decision-making or policy setting is a critical mistake, whether it is energy companies on climate change or meat companies in the diet wars. Meat has been with us since the beginning of evolution and the last two articles have shown it has a vital role to play in human health by providing hard-to-replace nutrients. While we have heard about health risks in recent years, the conclusions are overblown and based on low to very-low-quality evidence – a nuance that does not transfer well through media to the public.

When PETA shows up on a list of 98 organizations and individuals in a letter to IPCC, the meat industry must maintain a strong voice. Our social license to carry on developing the meat industry requires a rethink of messaging and where shortcomings exist, a rethink of production methods. Using climate change as cover, niche special interest groups like PETA are finding effective ways to affect policy. Thankfully the American public at least, is still supportive of the meat industry and rightly questioning blanket negative connections to the environment and health risks.?More science is needed but it is important that clear messaging is the result through the media. Otherwise, news articles labeled as science remain an unhelpful noise and will continue to result in poor policy.

- - - - -

Part 4 will turn attention to meat and the environment summarizing “Ecosystem management using livestock: embracing diversity and respecting ecological principles" Thompson et al. 2023.

?

Literature focus of Part 3:

Johnston et al. 2023 Non-communicable disease risk associated with red meat and processed meat consumption - magnitude, certainty and contextuality of risk? Animal Frontiers 13(2):19-27.?https://doi.org/10.1093/af/vfac095