Earlier this year, the U.S. Department of Health and Human Services (DHHS) in conjunction with the U.S. Department of Agriculture (USDA) released the long awaited 8th edition of the Dietary Guidelines for Americans. As in prior iterations of this federal publication, all stakeholders, including the industry and academia, have received these current guidelines with a heavy dose of scrutiny. Most clinicians (author included) typically embrace these updates via a passing glance at a bland news summary. Yet it is important to stay attuned to the controversies behind these new guidelines, as they may help us better understand the limitations of dietary policy and nutritional science and thus help us better engage and educate our patients in nutritional health.
Why the guidelines exist, and why it matters
Modern nutritional science took off in the1930s, when Vitamin C was isolated and verified as the protective necessary component to fend off scurvy. Once it was ascertained that micronutrients play a role in disease prevention, the following decades resulted in an explosion of nutritional studies demonstrating similar vitamin deficiency-disease links (e.g. iodine deficiency and goiter).
As improvements in agriculture and food processing rapidly diminished nutritional deficiencies in the U.S., national dietary guidelines took on a more prominent public health role by focusing more heavily on chronic disease prevention. It remains to this day that a primary focus of the federal nutritional guidelines is to promote health by preventing chronic disease attributable to poor diet. (1) But the Dietary Guidelines for Americans do much more than to merely give advice.
Under the National Nutritional Monitoring and Related Research Act of 1990, the guidelines are also required to aide the development and maintenance of federal policies and programs related to food and nutrition. (2,3) Given ~ 80 million U.S. citizens are fed on federal subsidies through programs like the Older Americans Act Nutrition Program (OAA NP) and the Supplemental Nutrition Assistance Program (SNAP), these guidelines have major influence on what goes into many American meals. (4) These formal recommendations also drive nutrition policy across the globe, with many nations simply adopting the US recommendations for their own. (5) Thus, the committee behind the Dietary Guidelines for Americans have huge authority in both national and international food policy.
How the guidelines are updated, and why it matters
By federal law, the Dietary Guidelines for Americans are required to be updated every 5 years. To do this, the Secretaries of the DHHS and USDA form an external Dietary Guidelines Advisory Committee made up of 10-15 select researchers in the fields of nutrition and medicine. They then review the past guidelines (last published in 2010) and analyze any new compelling dietary studies in the last 5 years. Prior to a final updated publication, the committee submits a scientific report and offers a period of time where the public, including industry and lobbies, is able to comment. (2,3)
Much criticism has been raised regarding the selection and function of this committee. These are mostly broken down to the following three potential issues:
- The committee members minimally participate in the minutia of the review, and instead use government staff and volunteers to do much of the analysis (4)
While it is not uncommon for federal committees focused on sizeable endeavors to use outside assistance for much of the grunt-work and for dietary studies to be largely funded by the food industry, there appears to be a large transparency issue with the make-up and process of this committee that may have a lasting impact on what nutritional advice makes the cut (and what doesn't) in the final reports of the dietary guidelines.
What is in (and what is not in) the current guidelines, and why it matters
The current round of dietary recs made in this 8th edition are mostly repackaged statements generated from prior editions. Advice remains consistent when it comes to promoting fruit, vegetable, whole grain, low-fat dairy, lean meats and oil intake. The guidelines also call for limiting sodium, simple sugars and saturated fat. (3,6) A few tweaks have been made on the latter recs, specifically limiting added-sugar intake to less than 10% of daily calories and removing the restriction on the percentage of calories from total fat. (7)
A major concern of this updated guideline is regarding the wording and delivery of its recommendations. For example, while the scientific evidence report from the Dietary Guidelines Advisory Committee recommended reducing consumption of sugary drinks and processed red meats, the guidelines themselves fail to add them into their primary recommendations. Roberto Ferdman of the Washington Post discusses this concern at length in his exposé entitled: "We Don't Know What To Eat:"
"But the message is pretty confusing. When they tell you what to eat, they speak directly, naming foods that are easy to identify. When they tell you what to avoid, they speak opaquely, referring to nutrients that are hard to grasp....In place of foods we know--things we understand well and can eat more of or try to avoid--are nutrients we've heard but likely misunderstand. Instead of sugary drinks, we're told to limit sugar; instead of red meat, we're told to limit saturated fat; instead of processed foods, we're told to limit sodium." (8)
This issue in content delivery again raises the question of conflict of interest and transparency issues among the dietary committee and other stakeholders such as the food and beverage industry.
Beyond these concerns, much of the research used to generate these guidelines have been subject to intense scrutiny due to the intrinsic flaws of study design. (9,10)
And so the critics ask: How strong are the data behind these recommendations?
Which studies are used to generate these guidelines, and why it matters
Where evidence-based medicine highly lauds the randomized control trial (RCT) as a "gold-standard" in identifying causation between an experimental variable (e.g. drug, therapy) and an outcome (e.g. death, prevention of heart attack), it is exceptionally difficult and resource-intensive to design a high-quality RCT studying meaningful outcomes between various diets. Although a few RCTs do exist and have made it into the Dietary Guidelines (e.g. PREDIMED), most studies that were selected for analysis were observational studies that focused on generating associative links between diet and health rather than causative links.
The data collection methodology found in most dietary studies is also highly controversial. Short of locking participants up in a room for several years in order to pick apart meals and weigh the various food contents, most methods are largely based on collecting memory-based dietary assessments (M-BMs). (11) Typically, this type of data collection calls upon participants to accurately fill out food diaries, recall surveys and/or food frequency questionnaires.
The biases of M-BMs are aplenty, including:
- Recall bias - did the participants remember that they ate that delicious fried chicken?
A final word on food surveys: much of the data generated from them can produce huge data sets with many variables. Given the large size of uncontrolled variables, it has been questioned that many "statistically significant" associations found in studies using these surveys are falsely positive associations discovered by chance. (9)
Take home points
Despite a huge surge in nutrition science within the last half century, there remains a lack of consensus on what makes a healthy diet. We've mastered the nutritional deficiency, but we continue to struggle unlocking the dietary link between food and chronic disease.
In order to avoid the trap of highlighting specific food associations through large survey data sets or from studies designed to assess shaky surrogate outcomes, it may be more beneficial to instead focus our time as clinicians to counsel patients on overall health-diet patterns and the value of portion control.
Because our current understanding of population dietary health, reflected by the controversy over the current U.S. Dietary Guidelines, continues to involve issues with transparency and design, it is ever more important to work with our patients as individuals to find a reasonable diet that is personally tailored to maximize adherence and meet specific weight goals.
Originally written as an opinion piece for One Medical Group
References:
1) Mozaffarian D. Dietary and Policy Priorities for Cardiovascular Disease, Diabetes, and Obesity: A Comprehensive Review. Circulation. 2016 Jan 8. Link
2) DeSalvo KB, Olson R, Casavale KO. Dietary Guidelines for Americans. JAMA. 2016 Jan 7:1-2. Link
3) Dietary Guidelines Executive Summary. (n.d.). Link
4) Eades, M. Dietary Guidelines for Americans: Science or ...? (2015). Link
5) Teicholz N. The scientific report guiding the US dietary guidelines: is it scientific?
BMJ. 2015 Sep 23;351:h4962. Link
6) Nissen SE. U.S. Dietary Guidelines: An Evidence-Free Zone. Ann Intern Med. 2016 Jan 19. Link
7) Phares, E. (2016, January 7). New Dietary Guidelines remove restriction on total fat and set limit for added sugars but censor conclusions of the scientific advisory committee. Link
8) Ferdman, R. A. (2016, January 07). We don't know what to eat. Link
9) Aschwanden, C., & Barry-Jester, A. M. (2016, January 06). You Can't Trust What You Read About Nutrition. Link
10) Unite For Sight. (n.d.). The Challenges and Failures of Nutrition Studies. Link
11) Archer E, Pavela G, Lavie CJ. A Discussion of the Refutation of Memory-Based Dietary Assessment Methods (M-BMs): The Rhetorical Defense of Pseudoscientific and Inadmissible Evidence. Mayo Clin Proc. 2015 Dec;90(12):1736-9. Link