The drastic reduction in animal foods that accompanies many plant-based diets will worsen already common micronutrient and protein deficiencies, warns a paper published this week in the scientific journal Frontiers in Nutrition.
The perspective article, written by Dr Alice Stanton of the Royal College of Surgeons in Ireland and the University of Medicine and Health Sciences, examines the reliability of claims that plant-based diets, with very limited intake of animal products (ASFs), provide adequate nutrition and offer protection against chronic disease.
Dr Stanton's analysis shows that the protection offered by a plant-based diet against chronic noncommunicable diseases (NCDs) is more strongly associated with lower calorie and salt intakes, and higher intakes of fruits, vegetables, nuts and whole grains, than with lower intakes of ASFs.
Her article raises numerous questions about the credibility of the scientific findings used to support the anti-meat recommendations of the EAT-Lancet Planetary Health Reference Diet, published in 2019.
The diet, which made headlines around the world, recommended getting only 13 percent of calories in a diet from animal products.
The EAT-Lancet Committee was confident that the diet, despite its low ASF content, would meet all the nutritional needs of both adults and children over two years of age.
"This confidence was surprising for a number of reasons," writes Dr. Stanton, citing published studies showing that as the percentage of energy from ASFs in the national food supply decreases, the prevalence of micronutrient deficiencies increases exponentially.
She also pointed to another recently published systematic literature review on the topic, which found "clear evidence" that dietary changes aimed at reducing environmental impacts resulted in lower intakes and status of a wide range of micronutrients that pose a risk to public health.
And another published article found that reducing animal protein, even by up to 50 percent, led to significant decreases in vitamin B12 and iodine intake and status.
Further research has revealed errors in the assumptions and methods used, showing that any mortality-reducing effect of the EAT-Lancet diet is "no greater than the impact of changes in energy expenditure that would prevent underweight, overweight and obesity alone".
Strict adherence to the EAT-Lancet reference diet provided "no additional protection against mortality," according to additional research, including the Oxford part of the European Prospective Investigation into Cancer and Nutrition study, the Prospective NutriNet-Santé Cohort study, and the Prospective Urban Rural Epidemiology (PURE) study.
The dangers of ignoring best practices in nutritional epidemiology by using low- or very low-certainty evidence in developing guidelines or calculating global health statistics were illustrated by the "very different" Global Burden of Disease (GBD) risk estimates for unprocessed red meat included in the GBD 2017, GBD 2019 and Burden of Proof (BoP) 2022 studies.
In the 2017 GBD estimates, based on associations with colorectal cancer and diabetes mellitus, the GBD Risk Factor Collaborators estimated that diets high in unprocessed red meat were responsible for 25,000 deaths and 1.3 million disability-adjusted life years (DALYs) globally.
However, in 2019, GBD staff reported that they had found sufficient evidence for additional causal links between red meat consumption and ischemic heart disease, breast cancer, cerebral hemorrhage, ischemic stroke, and subarachnoid hemorrhage.
They thus estimated that 896 thousand deaths and 23.9 million DALYs were attributable to unprocessed red meat consumption. This represented 36-fold and 18-fold increases, respectively, compared to the GBD 2017 estimates for deaths and DALYs.
However, further investigation by Dr. Stanton and others revealed that the evidence for the 2019 estimates came from internally conducted, newly conducted, systematic reviews and meta-regressions that had not been peer-reviewed or published. Furthermore, no certainty assessment had been performed.
Many in the scientific community questioned the reliability of these drastically changed estimates and rightly called for publication of PRISMA-compliant reports (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) on the newly conducted systematic reviews.
In response to scrutiny of their report, GBD staff publicly acknowledged that their 2019 risk estimates of unprocessed red meat for NCD events were inappropriately overinflated.
Dr Stanton noted that one of the EAT-Lancet commissioners, Professor Jessica Fanzo, recently confirmed that their first version of a planetary healthy diet would result in significant deficiencies in essential micronutrients.
Despite requests to the GBD authors and to the editors and ombudsperson of The Lancet, no corrections have been made to the published article and the 2019 risk assessments remain unchanged on the GBD website.
There are therefore still significant doubts about the accuracy of these GBD 2019 risk estimates.
Despite these important limitations, the GBD 2019 Risk Factors Study is still widely cited-over 3,650 times in the past four years.
Many have used the GBD 2019 as 'primary evidence' of the negative consequences of consuming red or processed meat.
"It is concerning that the monthly number of publications using these erroneous estimates continues to rise," Dr. Stanton writes.
She said it is clear that any evidence that moderate consumption of ASFs is harmful to human health is "weak and uncertain".
It was also clear that the drastic reduction in ASFs advocated by many plant-based diets will exacerbate the already prevalent micronutrient and protein deficiencies worldwide.
"Scientists, policymakers and anyone involved in the food system must be extremely cautious about any reports, guidelines or estimates of global health that are not rigorously and transparently evidence-based.
"A wide range of sustainably produced, nutrient-rich animal and plant foods, in appropriate, evidence-based amounts, should continue to be included in national and international dietary guidelines.
"Further research, funding and efforts should be directed towards objective and reliable measurements and improvements in the sustainability of each component of the food system; production; processing; distribution; retail; consumption; and waste management."
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