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Scientists question reliability of claim that red meat causing rise in deaths 

A group of scientists have written to the medical journal, The Lancet, to challenge the widely-reported claim made by the Global Burden of Disease (GBD) report that red meat consumption is linked to an apparent major rise in deaths and diseases worldwide. 

The GBD study made headlines across the world in 2019 when it claimed that the estimate of deaths attributable to unprocessed red meat intake had dramatically jumped 36-fold. The report set the theoretical minimum risk exposure level – the level of ingestion for a food at which it can be said that it can cause minimum harm – at zero. This had the effect of positioning unprocessed red meat as a harmful food – but now scientists are challenging the authors of the GBD study to produce the evidence.

A group of medical, health and food science professors — including Prof Patrick Wall of UCD – have questioned the reliability of the GBD claim, and focused in particular on the data used by GBD, which, they say, has not been available for scrutiny by other scientists.

They also say that the nutritional benefits of red meat were ignored in the GBD claim – and they say that the findings should not be used to influence health and agricultural policies until the data is presented and verified.

The scientists note that GBD produced a similar report in 2017, where red meat was ranked as the least important of 15 dietary risk factors studied in relation to diseases such as heart disease and cancer.

But in 2019, GBD dramatically changed their analysis of risk factors. As the Lancet letter points out:  “In 2019, a diet high in red meat was reported to be responsible for 896,000 deaths and 23.9 million disability adjusted life-years (DALYs).

“By contrast, the GBD 2017 analysis only attributed 25,000 deaths and 1.3 million DALYs to diets high in red meat and red-meat intake was the least important of 15 dietary risk factors.

“Hence, by comparison with previous estimates, the 2019 estimates of deaths attributable to unprocessed red-meat intake have increased 36 fold and estimates of DALYs attributable to unprocessed red-meat intake have increased 18 fold,” the scientists pointed out..

“Is this reliable?” they asked. “We have some serious concerns about the most recent GBD systematic analysis of risk factors.”

They reveal that the GBD analysis in 2019 adopted a change in approach when assessing risk – but said that GBD had not released the full data for their conclusions.

All previous GBD Risk Factor analyses used data from published peer-reviewed systematic reviews and meta-analyses, as well as the World Cancer Research Fund criteria for convincing or probable evidence of risk–outcome pairs, to construct the relative risk curves and to determine the [theoretical minimum risk exposure level] for each risk factor” the scientists explained.

“These findings of additional causal relationships for red meat are not in agreement with other recently conducted systematic reviews and meta-analyses,” they elaborated in the Lancet letter.

The Nutritional Recommendations (also known as NutriRECS) international consortium performed four parallel systematic reviews of randomised trials and observational studies. The consortium reported finding low to very low certainty evidence that diets lower in unprocessed red meat might result in very small reductions in risk of cardiovascular disease, stroke, myocardial infarction, type 2 diabetes, and overall lifetime cancer mortality. The 2018 World Cancer Research Fund’s Continuous Update Project Expert Report judged the evidence for a link between red meat intake and breast cancer to be limited and that no conclusion could be reached regarding a causal or protective relationship.”

“In attempting to understand these highly divergent conclusions, it is problematic that the GBD 2019 analysis provides little information concerning their updated systematic review,” the scientists said.

“With regard to data inputs, GBD 2019 does indicate that 92 sources are used in the estimations of relative risk of diets high in red meat. However, those 92 publications are not specifically identified, and we cannot find any reporting of GATHER items 3–6, which pertain to how the data from each source were identified and accessed, the inclusion and exclusion criteria, the characteristics of the populations, the data collection methods, and any potentially important biases,” they wrote.

“This non-adherence to agreed best practice is deeply concerning.”

They also say that the decision of GBD 2019 study to lower the minimum risk level for red meat from 22·5 g per day to 0 g per day was “counterintuitive given the role of meat in evolutionary diets and in contemporary hunter-gatherer populations, in which cardiometabolic diseases were and still are uncommon.”

“Furthermore, recently published results from one of the largest multinational studies, which was conducted in five continents and examined the association between different types of meat and health outcomes, the Prospective Urban Rural Epidemiology study, contradicts this premise,” they say.

The scientists insist that it is “of considerable importance that the GBD 2019 Risk Factors Collaborators provide the empirical evidence for this change in [theoretical minimum risk exposure level] and confirm that there was no projection beyond the available evidence.”

“Since publication, GBD 2019 has been cited by 635 documents, including 351 scientific papers and nine policy documents,” they pointed out, calling on the GBD authors to “clarify where the peer-reviewed publications of their updated or new systematic reviews are.”

Unless, and until, all new or updated reviews and meta-analyses pertaining to all dietary risk factors are published, having undergone comprehensive independent peer review, we think it would be highly inappropriate and imprudent for the GBD 2019 dietary risk estimates to be used in any national or international policy documents, nor in any regulatory nor legislative decisions,” they said.



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