Tough Going for Guidelines

Developing guidelines can be tough going. Just ask the folks who worked without pay on the new cholesterol guidelines for five years, only to find them under attack within days of being released. Dietary guidelines are no less challenging, as we learned at the ASN conference on Advances and Controversies in Nutrition 2013.

Johanna Dwyer opened the conference with an excellent review of history, successes, and misfires in developing dietary guidelines for Americans. She described the events that led to the publication the first-ever dietary goals for Americans in 1977: increased carbohydrate consumption, reduced total, and saturated fat consumption.

Dwyer commented that strong evidence-based dietary guidelines provide a framework for reducing chronic disease risk factors that is being integrated into nutrition programs such as school lunches. Among the “misfires” of dietary guidelines, she highlighted the USDA MyPyramid food guide, which became such a joke that it had to be quickly replaced by MyPlate. Quickly in the world of nutrition guidelines means it took six years.

David Allison provided excellent insight into the challenges of sorting out the impact of different foods on health and weight status. He cited three issues that get in the way of having clear and compelling evidence for dietary recommendations:

  1. Defining the Question. The answer that research provides very much depends on the question that is asked. All too often the question or hypothesis is not defined clearly at the outset, leading to ambiguous, conflicting, or meaningless results.
  2. Randomized Experiments. Observational studies are no substitute for well-designed, randomized experiments. Allison provided numerous example of observational nutrition findings that do not hold up when tested in a randomized experiment.
  3. Careful Experimental Design. The devil is in the details of experimental design for nutrition studies. Short-term studies are often inadequate. Perceptions, beliefs, expectations, and palatability of foods are among the many factors that can influence nutrition research findings.

Declaring that the available evidence is “good enough” can lead to serious unintended consequences when incomplete evidence is used as the basis for nutrition policy.

After all, trans fats became broadly used in part because of the effort to reduce saturated fats in the American diet. And now, we’re still trying to fix that mistake.

Click here for more on Dwyer’s presentation and here for more on Allison’s presentation.

USDA Food Pyramid, image © Akron Beacon Journal

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