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Researchers at the University of Ottawa have revealed significant methodological flaws in the systematic reviews used to create the 2020-2025 US Dietary Guidelines for Americans, a series of eating recommendations that, while not consulted by most Americans daily, feed into meal plans and choices in most medical establishments, correctional facilities, and schools.
They are also used as a basis for regulations in food and supplement marketing, including whether products can be referred to as “good sources” of things like fiber or protein.
In short, whether you’ve ever taken counsel from the USDA guidelines or not, you’ve likely been exposed to them unknowingly.
Worryingly, the recent overview of the literature by the team from Ottawa identified multiple flaws of the kind that might prevent a scientific paper from making it through peer review.
Many Americans, if asked, would likely reply that something like dietary guidelines in the nation that leads the world in chronic diet-linked diseases like obesity and diabetes would be well-researched and of the highest quality, but the USDA uidelines were only able to satisfy 63% of the requirements of the average review paper, placing it in the category of “critically low quality” science.
“We identified several errors and inconsistencies in the search strategy and could not reproduce searches within a 10% margin of the original results,” the authors report in their paper, published in the American Journal of Clinical Nutrition.
Additional problems identified were inadequate reporting of methods, and perhaps more damning was a lack of proper justification for analysis choices.
A history of failure
WaL has reported in several instances on shortcomings within the USDA Dietary Guidelines. In 2022, WaL reported that they fail to expound on the importance of choline in the human diet, something deficient in over 90% of Americans. In supplemental materials, the guidelines authors avoid mentioning the richest sources of choline for humans, which is meat in general and organ meats in particular, while listing “chocolate cake” and “fast food” breakfast sandwiches as good sources.
In 2023, WaL reported that a Control-F search for the word “spice” reveals that the USDA Dietary Guidelines have no mention of herbs or spices apart from saying how they are important culturally. Herbs and spices are calorie-for-calorie the most nutrient-dense foods in the human diet.
Also in 2023, WaL examined a study that was selected to be included as cited research in the upcoming changes to the guidelines for 2025-2030 that attempted to meet every micronutrient requirement using only processed and ultra-processed foods, and that multiple members of the study group accepted money and or held positions with soybean interests United Soybean Board and Soy Nutrition Institute Global.
The guidelines are made as follows: topics to be examined are selected and a committee is appointed to review current scientific evidence and develop a report. The committees rely on “systemic reviews” of individual elements in a topic produced by a Nutrition Evidence Systematic Review (NESR) team. Systemic reviews are the topline publication on health topics, in which hundreds of studies and meta-analyses (studies of studies) are combined to form a sort of state-of-the-art explanation.
These NESR teams, which are boasted to include public health experts and epidemiologists who specialize in making systemic reviews, were pinned by the Ottawa team for making strange choices for the papers they chose to include in their reviews and failing to explain why. In this case, it was the total absence of meta-analyses and no justification for this absence. Meta-analyses have led to many nations and institutes abandoning recommendations about limiting red meat consumption due to cancer or heart disease risk, even though decades of studies have suggested these connections.
Another key absence is around 5,000 different results in scientific databases, such as PubMed, when the Ottawa authors attempted to recreate those reportedly used by the NESR teams. When the authors followed the same procedure for retrieving literature to be included in one systemic review in particular that informed the guidelines, they identified just over 10,000 items when using the same search parameters. The NESR teams report to have found 5,600 that were then subject to the removal of 2,071 items that were duplicates.
Furthermore, the searches used by one NESR team were analyzed and found to be extremely unprofessional. Issues include a lack of using quotation marks to narrow search fields, and the use of filters to exclude specific publication types like editorials, comments, retracted publications, retraction notices, and systematic and narrative reviews which not only contain relevant data, but also would reveal if data included by the NESR’s had subsequently been altered, retracted, or criticized.
It makes for difficult reading for someone open to interpretation of failure as more than just negligence, and another sign that the USDA Dietary Guidelines for Americans should probably be avoided for more up-to-date and high-quality research. WaL
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PICTURED ABOVE: The USDA building in Washington DC. PC: CC 3.0. SA Michael Kranewitter
