Commentary: Rigorous science must decide dietary guidelines to combat health epidemic

It’s been 35 years since the government launched its Dietary Guidelines for Americans, yet the nation continues to suffer from ever-rising rates of obesity and diabetes.

“We are on the wrong trajectory,” testified Health and Human Services Secretary Sylvia Burwell this month before a House panel examining the dietary guidelines.

Democrats and Republicans on the House panel also expressed serious concern.

“Have these guidelines failed?” questioned panel member Rep. Glenn Thompson, R-Pa. “They don’t seem like they’re accomplishing their objective.”

The panel’s top Democrat Collin C. Peterson of Minnesota echoed the sentiment: “I just want you to understand from my constituents, most of them don’t believe this stuff anymore … and so that’s why I say I wonder why we’re doing this.”

Members from both sides of the aisle overwhelmingly agreed with what many of us responsible for the science behind the guidelines have known for years — it’s time to take a hard look at how we might have gone wrong.

As a former member of the committee charged with developing the federal government’s dietary guidelines, I can speak from experience when I say that the process to develop the recommendations does not assure that the best science is used.

And this is a major cause for concern.

 
The recommendations have an overwhelming and extraordinary impact on Americans in every part of the country. Representing the federal government’s official nutrition policy, the guidelines inform medical and nutrition education nationwide, influence and largely determine the basket of foods in USDA feeding assistance programs such as the National School Lunch Program and the Special Nutritional Program for Women, Infants and Children (WIC). The guidelines shape American eating habits, and as such must be informed and reinforced by the strongest science available.

So how is the process to develop these recommendations falling short?

 
First, the scientific experts serving on the committee are often not involved in analyzing the latest studies. Reviewing the previous five years of science — which is every committee’s mandate – is an enormous undertaking, and experts appointed to the committee are usually academics who already have full-time jobs. As a result, the responsibility falls to government staff, reviewing scientific literature alongside a network of volunteers and professionals. Although committee members do their best to be directly involved, they are often limited to simply accepting the analysis without time for questioning.

This process was significantly strengthened in 2010, with the introduction of a rigorous, systematic “checklist” that helped determine the strength of individual studies. The effort, commonly referred to as the Nutrition Evidence Library, is housed at the Department of Agriculture. The committee I served on was responsible for establishing this backstop, and some of us were alarmed to see that the 2015 committee did not use this system for a majority of its literature reviews, including those on many key issues.

Coming to an agreement about science-based recommendations is never easy, but many of the problems the science community faces today are self-inflicted.

For example, the first responsibility in any scientific analysis is the definition and consistent use of its terms. Yet the expert report for the dietary guidelines has commonly grouped together studies with inconsistent definitions. In some studies, the category of “vegetables,” included potatoes — in others it did not. The “meat” category differed across studies, sometimes including eggs and fish.

While this may just seem like meat and potatoes to some, for scientists it’s the difference between failure and success — to stave off inconsistencies that can ultimately invalidate a report’s accuracy.

Inconsistent inclusion of studies is another problem. While the guidelines are meant to prevent disease rather than treat it, a point U.S. Department of Agriculture Secretary Tom Vilsack emphasized in this week’s House hearing, many of the bedrock studies cited to support the dietary guidelines address treatment and not prevention, such as the Dietary Approaches to Stop Hypertension trials.

Most significantly, over the years, we’ve made recommendations based on an inconclusive kind of science that can establish associations but not causation. Founding our advice upon these kinds of studies has proven to be risky: the recent reversal on dietary cholesterol and new questioning about salt and saturated fats are prime examples of this. We need to be sure that all recommendations are based on rigorous clinical trials, and where those trials are lacking, encourage funding for them.

It’s further troubling that no one is assigned to take the long view — no one looks at the body of literature on a given topic to determine if it should be reinterpreted in light of new findings and new questions. This should be an important course of action in the future, especially around key issues such as the impact on disease of dietary fat, carbohydrates and salt.

At the end of this year, the federal government will issue a new set of dietary guidelines, but what’s clear to many in the scientific community is that the dietary guidelines report is not ready for primetime. The process under which they were developed clearly needs enhancing to ensure that Americans are being provided the strongest, most accurate recommendations based on the most rigorous science available.

Vilsack and Burwell are in the process of reviewing that report, to examine the quality of the arguments behind the report’s science, claims and recommendations — and I encourage them to take on that responsibility with an eye toward ensuring that the final recommendations are based on the most recent and best science.

It would also be wise before 2020 — when the next set of dietary guidelines will be updated and issued again – to have a thorough review by an outside authority, such as the National Academy of Sciences, of both the science and process of the guidelines.

The future for nutrition scientists depends upon our being able to deliver advice that improves health.

 
If that process is outdated or flawed, then we must improve it so that we can reinforce and restore a commitment to rigor needed in our field, regain the public trust, and most importantly, help the nation restore its health.