Our Outdated, Unscientific Dietary Guidelines
New Paper in Nat'l Academies of Sciences' Journal finds Major Flaws
Why do kids in public schools get served donuts and orange juice for breakfast, a meal guaranteed to send blood sugars soaring, rather than a sugar-free, protein-rich option, like scrambled eggs? The unfortunate answer is that the donut meal accords with our nation’s top nutrition policy, the U.S. Dietary Guidelines for Americans, which despite its influence has been found by a new study to contain outdated science and not reflect the “preponderance of scientific and medical knowledge,” as required by law.
These and other disquieting findings are the subject of a paper I co-authored, published in a journal of the nation’s highest scientific body, the National Academies of Sciences, Engineering, and Medicine. To my knowledge, it is the most comprehensive critique of the Dietary Guidelines to date, written by top experts who include three former members of the very expert committees (called the Dietary Guidelines Advisory Committee, or DGAC) that reviewed the science for past versions of the guidelines. Yet now, they view this policy as flawed.
In plain terms, we found that the U.S. guidelines—despite being followed by all federal agencies and most schools, hospitals, doctors and dieticians— cannot be guaranteed to reflect trustworthy advice for the urgent task of combating obesity, diabetes or any other chronic disease.
This post is wonky but relevant to people interested in good policy or how food policy affects their children, parents, schools, communities, and more.
This post may also interest anyone who believes a diet “rich in fruits, vegetables, legumes, cereals/whole grains, nuts, fish, and unsaturated [vegetable] oils and low in meat and high-fat dairy” is the key to better health—because that’s exactly the diet at the heart of the guidelines.
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Criticism of the evidence underpinning this dietary advice goes back decades. A report in 1980 by the National Academies of Sciences that examined the foundational studies for the Guidelines concluded that the proposed diet had “generally unimpressive results,” and the director of the National Heart, Lung and Blood Institute urged restraint, noting a lack of scientific evidence for the guideline recommendations and the potential for unintended consequences.1
More recently, a former DGAC member wrote:
“Despite our evidence-based review lens where we say that food policies are ‘science based,’ in reality we often let our personal biases override the scientific evidence.”
In 2017, the National Academies of Sciences, Engineering, and Medicine (NASEM) weighed in with two reports, at the behest of Congress. The NASEM found that the guidelines process needed to “improve transparency” and “strengthen scientific rigor.”
"To develop a trustworthy DGA,” the report states, “the process needs to be redesigned.”
The NASEM issued 7 recommendations, yet five years later, six of these had not been implemented in full, and the seventh could not be verified due to lack of information, according to a follow-up NASEM report published this year. The USDA has resisted reforming even the most glaring problems, such as the lack of public disclosure of conflicts of interest on the DGAC committee, when such disclosures on guidelines committees are now the norm. (Fully 95% of members on the 2020 DGAC were found to have at least one tie to industry, and a majority had 20 such relationships or more.)
In line with the NASEM, our paper found a number of serious problems with the guidelines process. And on key topics—including dietary fat, saturated fat, and cholesterol—we concluded that the guidelines are no longer supported by the science, or are simply in error.
Major findings of our paper.
The law requires that the science underpinning the current guidelines be “current at the time the report [was] prepared,” but this was not the case with the most recent guidelines report, out in 2020:
The scientific reviews for the “Dietary Patterns” (the main dietary advice, i.e., the list of foods above) included studies only through 2012-2013, i.e., 8-to-9 years out-of-date at the time of the report’s publication.
The reviews for the “Birth-to-24 Months” recommendations included science only through mid-July 2016, which was at least 4 years out-of-date at the time of the 2020 report.
Guidelines Omit Major Bodies of Scientific Literature
The law also requires that the guidelines reflect the “preponderance of scientific and medical knowledge,” yet for the 2020 expert report:
The scientific literature on weight loss was omitted, “a questionable decision given that at least two thirds of Americans are overweight or obese and also that weight loss is widely considered an important intervention to reduce risk for type 2 diabetes and other health conditions,” as we wrote;
The scientific literature on low-carb diets was omitted (For more on how the science on low-carbohydrate diets has been buried, see my previous post).
USDA Taking Over; Outside Experts Marginalized
The scientific reviews, long overseen by outside experts on the DGAC, has been almost entirely usurped by the government agency overseeing these reviews, i.e., the U.S. Department of Agriculture (USDA). USDA staff don’t just conduct the reviews, they actually draft the conclusions. The committee is left with almost nothing to do and at this point may be seen as little more than window dressing. For instance, USDA officials:
Conducted the reviews on the “Dietary Patterns,” the very heart of the guideline recommendations, without any oversight of a DGAC;
Conducted 43 reviews on the “Birth-to-24-months” without any oversight of a DGAC.
From our paper: “We argue that this approach is the opposite from what both statute and the FACA [Federal Advisory Committee Act] regulation intend. The expert committee should be driving the scientific process, not marginalized in a process now overtaken by potentially conflicted federal agencies.”
When we say “conflicted,” we mean that in addition to telling people what to eat and not eat, via the dietary guidelines, the USDA also has a contrary duty to promote the food and agriculture industries. I would add that the USDA also has a revolving door, or perhaps even a ‘captured agency’ problem, with people overseeing the guidelines hired straight out of industry and then returning directly to it.
Guidelines Not Meant for Most People
The law says that the US guidelines are supposed to serve the "general public," but now, 60% of public has at least one diet-related, chronic disease, and the guidelines do not review the relevant science, i.e., the treatment of these diseases.
From our paper: "The DGA therefore no longer serves the general public.”
Some Advice is Contradictory or Doesn’t Reflect the Science
On specific dietary recommendations, our paper found:
On dietary cholesterol: The guidelines contradict its own science. The 2020 DGAC review found “insufficient evidence” to support a relationship between the cholesterol you eat and cholesterol levels in the blood. Yet the guidelines’ advice was nevertheless to keep dietary cholesterol “as low as possible.”
On the “low-fat” diet: From 2000 on, the guidelines have ditched any "low-fat" wording, explaining that low-fat “diets are generally associated with dyslipidemia (hypertriglyceridemia and low HDL-C concentrations),” which are indicators of increased risk for heart disease. Also: the low-fat diet “could engender an overconsumption of calories in form of carbohydrates, resulting in the adverse metabolic consequences of high-carb diets.” For these reasons, a DGAC Vice Chair said in 2015: “...there is no conventional message to recommend low-fat diets.”
Yet the 2020 guidelines limits total fat to between 20-35% of calories, which is, as we write, “a range of dietary fat intake that has historically been understood in the scientific literature as a low-fat diet.”
On saturated fats: We found “insufficient rigorous evidence” to support limits on these fats as protection against heart disease. The 2020 DGAC review ignored more than 20 review papers by independent teams of scientists from around the world which concluded that strong evidence is lacking for continued caps on these fats.
I’ve saved the most wonky bit for last, which are shortfalls in the process for reviewing the science. The bombshell here is that the USDA uses no recognized methodology. Established systems like “GRADE” and Cochrane2 have been developed to set rules around evaluating scientific evidence including such things as the risk of bias, precision, quality of evidence, and more. Like the authorities who determine rules for football, these recognized review standards are spelled out transparently, so that rules can be applied consistently and everyone understands how to play. Yet we found that the USDA has only the vaguest of rule books. The agency says it graded evidence following “a thorough assessment and consideration of the strengths and limitations of various study designs” but doesn’t give any hard details about how this assessment was done. We also found that the USDA rules varied from one review to another. It’s like one football game is played with 9 yards to the first down while another uses 10. When the rule book is vague, a game can be played any which way, and bias can creep in.
The process for the next update to Dietary Guidelines, which will be the rule of the land until 2030, has just begun. At this juncture, the National Academies has now published four documents— its own three reports and our paper--critiques that dovetail and make clear that significant reform is needed. The problems are so grave that until reforms are completed, our guidelines will be untrustworthy. And until reforms are completed, it will be donuts for breakfast and Doritos for lunch. We all have a stake in the health of the nation, and we ought to do better.
All source materials are cited in our paper. https://academic.oup.com/pnasnexus/article/1/3/pgac107/6647007?login=false
GRADE stands for Grading of Recommendations, Assessment, Development and Evaluations. Cochrane Reviews are conducted according to well-developed standards and are published in the Cochrane Database of Systematic Reviews. Both these standards for systematic reviews were mentioned by the NASEM as options for at least part of the USDA review methodology.