Setting the Scene

The world in 2024 faces climate and biodiversity crises, and food production and consumption contributes importantly to both crises. The food system is currently estimated to be responsible for about a third of total greenhouse gas emissions, and the conversion of natural ecosystems to agricultural land has been reported to be the largest threat to species extinction. Hence there is indeed a need to transform our food system so that all have access to healthy diets, while at the same time safeguarding the planet’s health. The details of how that is best achieved is the subject of considerable debate – how much change should come from each domain of the food system – how much change should come from food production, processing, distribution, retailing and consumption?

Many recent publications have identified dietary shift as a key food system transformation. Rather than recommending moderation of current consumption patterns, these papers require considerable reductions, or even total exclusion of animal sourced foods, particularly ruminant products (red meat and dairy), from the human diet. They propose that these dramatic dietary shifts would benefit both planetary and human health. In this presentation, the reliability of the claims for benefits for human health was examined.

Reports from two groups, namely the EAT-Lancet Commission on Food, Planet, Health,¹ and the Global Burden of Diseases (GBD) Risk Factors Collaborators^2-5 are examined in particular detail. This is because estimates and reports from these two groups are the most influential. Indeed, many other reports and policy papers cite evidence from these two groups, and/or use the same assumptions and analytical techniques.  

Because of data gaps and measurement challenges in nutritional science, most, if not all, of the reports recommending reductions in animal-sourced foods, have used global health estimates, rather than primary data, as evidence for their recommendations.  However, there are grounds for considerable concern in regard to the quality, transparency and validity of the data, assumptions and statistical modelling, used in the calculation of the global health estimates, which underpin the claimed human health benefits. These concerns are more fully described in a soon to be published perspective.⁶

Reflections on “Too Little”

The Scientific Group of the UN Food Systems Summit 2021 defined a healthy diet as “health-promoting and disease-preventing. It provides adequacy without excess, of nutrients and health promoting substances from nutritious foods and avoids the consumption of health-harming substances”. The World Health Organisation similarly describes healthy diets as “helping to protect against malnutrition in all its forms, as well as noncommunicable diseases (NCDs), including diabetes, heart disease, stroke and cancer.”

In the GBD 2019 Risk Factors Study,³ for both red and processed meats, the level of exposure associated with the lowest level of risk, called the theoretical minimum risk exposure level (TMREL), was, by default, set to zero. This was very puzzling, as the contribution of moderate consumption of red and processed meats to nutrient adequacy, appeared to be totally ignored. Red and processed meats are rich in all essential amino acids and also in many commonly lacking micronutrients, including iron, zinc, vitamin B₁₂ and vitamin D₃. Whilst red and processed meats are not the only sources for these nutrients, they are the most important bioavailable sources for many populations worldwide. If the current public health message advising moderate consumption of red and processed meats, as part of a healthy balanced diet, was to be replaced by GBD 2019 guidance that any intake of such meats was harmful, it is highly likely that the prevalence of child and maternal malnutrition, iron deficiency anaemia, and elderly sarcopenia, would be greatly increased. It is good that the GBD collaborators have recently revised their estimates for unprocessed red meat, stating that the 95% uncertainty interval for the TMREL is very wide (0-200g/day)⁴ – this indicates that the optimal intake of red meat could be as high as 200 grams a day.    

The EAT-Lancet planetary health reference diet does allow low quantities of red or processed meats and eggs to be consumed and includes moderate amounts of seafood and poultry. However, the diet largely consists of vegetables, fruits, whole grains, legumes, nuts and unsaturated plant oils - only 13% of calories in the diet are from animal source foods.¹

In 2019 the EAT-Lancet Commission were confident that this diet would meet all nutritional requirements of both adults and children older than 2 years. However, it has recently been acknowledged by at least some of the EAT-Lancet Commissioners, that this first version of the planetary health diet would result in significant essential micronutrient shortfalls.⁷ This particularly pertains to micronutrients found in higher quantities, and in more bioavailable forms, in animal source foods, such as vitamin B₁₂, calcium, iron and zinc. It appears that insufficient attention was paid to the latest evidence on recommended nutrient intakes, and to the differences in micronutrient bioavailability from various foods. In order to achieve micronutrient adequacy, intakes of animal source foods would have to be doubled, accounting for at least 27% of calories, and intakes of plant source foods that are rich in phytates, such as whole grains, pulses and nuts, would need to be considerably reduced.⁷  

In 2019 the EAT-Lancet Commission were also confident that widespread uptake of their recommended diet would reduce the incidence of non-communicable diseases and overall mortality – they estimated that approximately 11 million premature deaths among adults could be avoided, annually, through global adoption of the reference diet. However, when this hypothesis was recently tested using data from the Prospective Urban Rural Epidemiology (PURE) study, it was clearly demonstrated that close adherence to the planetary health diet provided no additional protection from major cardiovascular events, nor from mortality.⁸

Reflections on “Too Much”

Compared with the GBD 2017 estimates,² the GBD 2019 estimates of the risks of many dietary risk factors differed considerably.³ Disease burdens (as measured by deaths and disability adjusted life-years [DALYs]) attributed to diets low in fruit, nuts and seeds, vegetables, seafood omega-3 fatty acids, polyunsaturated fatty acids, vitamin A or zinc declined by more than 50%, whereas risks for diets low in legumes, or high in either processed meats or trans fats, more than doubled. However, the most substantial change in the 2019 estimates was the disease burden attributed to diets high in unprocessed red meat. The GBD 2019 Risk Factor collaborators reported finding “sufficient evidence supporting a causal relationship of red meat intake with colorectal cancer, breast cancer, type 2 diabetes, ischaemic heart disease, ischaemic stroke and hemorrhagic stroke”. They estimated that 896 000 deaths (95% uncertainty interval, 536 000–1 250 000) and 23.9 million (15.6-32.0) disability-adjusted life years (DALYs) were attributable to unprocessed meat consumption globally in 2019. This represented 36-fold and 18-fold increases over the GBD 2017 estimates, respectively.

Whilst all previous GBD analyses, including the GBD 2017 analysis, used data from published systematic reviews and meta-analyses, the evidence for the 2019 dietary risk factor estimates came from in-house, newly conducted, systematic reviews and meta-regressions, which had not been peer-reviewed nor published, and for which there were no assessments of certainty.  I and many scientists, including representatives of the Academy of Nutrition Sciences and the World Cancer Research Fund (WCRF), questioned the reliability of the dramatically changed 2019 estimates, and requested that PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) compliant reports of the newly conducted systematic reviews be peer-reviewed and published.^9,10 

It is good that these requests were eventually answered through publication of the Burden of Proof (BoP) study of the health effects associated with consumption of unprocessed red meat in Nature Medicine in October 2022.⁴ However, this publication raises further issues.

The relative risk curves and the conclusions of the BoP 2022 Study⁴ are very different from those reported in the GBD 2019 Risk Factors Study.³ This is particularly striking for the three cardiovascular outcomes. The GBD 2019 Study indicated that risks for ischaemic heart disease, ischaemic stroke and haemorrhagic stroke increased significantly even with moderate intakes of red meat (50g/day), and that risk increased further with greater intakes. By contrast, the relative risk curves of the BoP 2022 study are either considerably flatter (ischaemic heart disease and ischaemic stroke), or show a trend towards protection (haemorrhagic stroke). It is noteworthy that none of these BoP relative risk curves are statistically significant even with intakes as high as 200 g/day. The overall conclusions of the BoP 2022 study are that there is no or only very weak evidence that unprocessed red meat is associated with any increased risk. 

The marked disparities between the conclusions of the GBD 2019 and BoP 2022 reports concerning unprocessed red meat, highlights the importance of expert peer review, of compliance with the PRISMA statement for all newly conducted systematic reviews and metanalyses, and of compliance with the GATHER (Guidelines for Accurate and Transparent Health Estimates Reporting) statement for all reports of global health estimates. These disparities also cast considerable doubt over the accuracy of the GBD 2019 estimates for all other dietary risk factors, given that these were also based on unpublished data.

Consequences of Delayed or Non-Correction of Errors and Limitations

Despite the above described limitations and errors being publically acknowledged by the EAT-Lancet and GBD authors respectively, no corrections have been applied to the published papers, and the estimates remain unchanged on their organization websites. 

The papers continue to be extensively cited, including such articles as the 2022 Report of the Lancet Countdown on Health and Climate Change.¹¹ This paper uses both the EAT-Lancet Reference Diet and the GBD 2019 Risk Factors Study as evidence for their model assumptions – this led the following headline finding “In 2019 11.5 million deaths were attributable to imbalanced diets, with 17% (2 million) associated with a high intake of red meat (800,000), processed meat (600,000) and dairy (600,000) consumption.” The estimates for excess deaths due to dairy consumption are particularly troublesome given the strong evidence that dairy protects against cancers, obesity, cardiovascular events, and total mortality.

Furthermore, the reports from the EAT-Lancet Commission and the GBD Risk Factors Collaborators continue to erroneously influence food policy decisions and international dietary guidelines, including the World Wildlife Fund’s Livewell Diet, and the Nordic Nutrition Recommendations 2023.

Key Messages

• Scientists, policy-makers and all involved in the food system should be extremely wary of reports, guidelines or global health estimates that;
  • Are not rigorously and transparently evidence-based, and/or
  • Ignore the protections against nutritional deficiencies and chronic diseases afforded by animal-source foods.
• The relationship between red meat and disease burden is most likely U-shaped;
  • Excess red meat consumption (>4 portions or 500g / week) may be associated with small (5-15%) increases in colon cancer (low certainty evidence).
  • Insufficient red meat consumption (<2 portions / week) is associated with very large (100-1000%) increases in anaemia, stunted childhood growth and cognition, osteoporosis and sarcopenia (high certainty evidence).
• The majority of the world’s population are not eating enough dairy nor omega-3-PUFA rich foods.
• Consumption of nutrient-rich, sustainably produced, animal-sourced foods, in appropriate evidence-based quantities, should continue to be included in national and international guidelines for a healthy, balanced diet.

References

1. Willett, W., J. Rockström, B. Loken, M. Springmann, T. Lang, S. Vermeulen, T. Garnett, D. Tilman, F. DeClerck, A. Wood, et al. 2019. Food in the Anthropocene: the EAT–Lancet Commission on healthy diets from sustainable food systems. Lancet 393:447–492.
2. Stanaway JD, Afshin A, Gakidou E, et al. Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet. 2018;392:1923–94.
3. GBD 2019 Risk Factors Collaborators. Global burden of 87 risk factors in 204 countries and territories, 1990-2019: a systematic analysis for the Global Burden of Disease Study 2019. Lancet. 2020;396(10258):1223-1249.
4. Lescinsky, H., Afshin, A., Ashbaugh, C. et al. Health effects associated with consumption of unprocessed red meat: a Burden of Proof study. Nat Med. 2022 Oct;28(10):2075-2082. doi: 10.1038/s41591-022-01968-z. Epub 2022 Oct 10. PMID: 36216940
5. Murray CJL, Lopez AD. Measuring global health, motivation and evolution of the Global Burden of Disease Study. Lancet 2018; 390: 1460-64.
6. Stanton AV. Is the use of substandard global health estimates in food policy decisions, which mandate large reductions in animal-source foods in the human diet, acceptable? npj Science of Food 2024; in press.
7. Beal T, Ortenzi F, Fanzo J. Estimated micronutrient shortfalls of the EAT-Lancet planetary health diet. Lancet Planet Health. 2023;7(3):e233-e237.
8. Mente A, Dehghan M, Rangarajan S et al. Diet, cardiovascular disease, and mortality in 80 countries. Eur Heart J. 2023 Jul 21;44(28):2560-2579.
9. Stanton AV, Leroy F, Elliott C, Mann N, Wall P, De Smet S. 36-fold higher estimate of deaths attributable to red meat intake in GBD 2019: is this reliable? Lancet. 2022;399:e23-e26.
10. Gordon-Dseagu VLZ, Wiseman MJ, Allen K, Buttriss J, Williams C. Troubling assumptions behind GBD 2019 on the health risks of red meat. Lancet. 2022; 400: 427-428.
11. Romanello M, Di Napoli C, Drummond P, Green C, Kennard H, Lampard P et al. The 2022 report of the Lancet Countdown on health and climate change: health at the mercy of fossil fuels. Lancet. 2022;400(10363):1619-1654.

Declaration of Interests

The author served as a non-remunerated member of the Irish 2030 Agri-Food Strategy Committee; is a non-remunerated member of the Irish Climate and Health Coalition, the Council on High Blood Pressure of the Irish Heart Foundation, the World Action against Salt, Sugar, and Health, the World Farmers’ Organisation Scientific Council, and Meat Technology Ireland; Acts as a consultant for Devenish Nutrition and Humanitiv; and owns stock in Devenish Nutrition, an agri-technology company specialising in sustainable food solutions.