Additionally, we are puzzled by the reference to more empirical standardised methods for selecting the TMREL for risk factors in GBD 2019. For protective factors, it appears that considerable care was taken to select the level of exposure with the lowest level of risk that was supported by the available data. The GBD 2019 Risk Factors Collaborators recognised that projecting beyond the level of exposure supported by the available studies could exaggerate the attributable burden for a risk factor. Hence, for protective dietary components, the TMREL was set using the 85th percentile of levels of exposure included in the published cohort studies or randomised controlled trials. By contrast, the TMREL for risk factors viewed as harmful was, by default, set to zero. Therefore, the red meat TMREL changed from 22·5 g per day to 0 g per day. The assumption of a red meat TMREL of zero is 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. It is of considerable importance that the GBD 2019 Risk Factors Collaborators provide the empirical evidence for this change in TMREL and confirm that there was no projection beyond the available evidence.
We further question if the totality of nutritional effects of red meat have been considered in the meta-regressions. If the TMREL is assumed to be zero, red meat would then de facto be presented as an inherently harmful food. This assumption would ignore the well documented nutritional benefits with respect to the supply of essential nutrients and bioactive components. If the current public health message advising moderate consumption of red meat as part of a healthy balanced diet is replaced by the message that any intake of red meat is harmful, this change will probably adversely affect iron deficiency anaemia, sarcopenia, and child and maternal malnutrition—these conditions and their associated risk factors are already responsible for considerably greater global disease burdens than a diet high in red meat, particularly in low-income and middle-income countries.
Since publication, GBD 2019 has been cited by 635 documents, including 351 scientific papers and nine policy documents. Using data from GBD 2019, Chung and colleagues concluded that global increases in the red and processed meat trade contributed to an abrupt increase of diet-related non-communicable diseases. The GBD 2019 Stroke Collaborators recently reported that greater numbers of stroke and subarachnoid haemorrhage DALYs were attributable to diets high in red meat, than were attributable to diets high in salt, in 11 of 21 world regions. Of great concern is the extensive quoting of GBD 2019 risk factor data in the evidence document of the UK's National Food Strategy. Figures in this policy document indicate that diets high in red meat are responsible for greater numbers of DALYs than diets high in salt, trans-fatty acids, or sugar-sweetened beverages.
Given the substantial influence of GBD reports on worldwide nutritional policy decision making, it is of considerable importance that the GBD estimates are subject to critical scrutiny and that they continue to be rigorously and transparently evidence-based. Hence, we call on the GBD 2019 Risk Factors Collaborators to address two key concerns. First, the GBD 2019 Risk Factors Collaborators should clarify where the peer-reviewed publications of their updated or new systematic reviews are that comprehensively address the 27-item PRISMA statement and the 20-item GATHER statement checklists; that justify the updated dose–response curves of the relative risks of red meat for breast cancer, colorectal cancer, type 2 diabetes, ischaemic heart disease, ischaemic stroke, haemorrhagic stroke, and subarachnoid haemorrhage; and that provide the empirical evidence for the changing of the red meat TMREL from 22·5 g per day to 0 g per day. Finally, the GBD 2019 Risk Factors Collaborators should clarify if the additional deaths and DALYs from iron deficiency anaemia, sarcopenia, and child and maternal malnutrition that would result from the imposition of a red meat TMREL of zero have been included in the GBD 2019 estimates.
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.