Do Dietary Guidelines Do More Harm Than Good?
I recall an old colleague of mine in the United Nations who kept a sign on the wall behind his desk,
"Don't Just Do Something, Stand There!"
It was his way of trying to get people to think things through thoroughly, before rushing headlong into an intervention.
Legislation on food labeling , recommendations on Daily Values and the Dietary Guidelines are all examples of interventions that would have benefitted from my friend's advice. About the only thing that everyone can agree upon is that they are all largely ineffective and hold scant benefit for the consumer.
In a recent article entitled, "A Call for Higher Standards of Evidence for Dietary Guidelines," Am J Prev Med 2008: DOI: 1016/j.amepre.2007.11.017., authors Marantz, Bird and Alderman make the case that with their weak standards of evidence and tendency to focus on individual nutrients, the national dietary guidelines might actually do consumers a lot more harm than good.
As an example, they used the guidelines developed against the consumption of dietary fat, promulgated in the late 1970s. The authors noted that people were inadvertently led into believing that if they limited their fat intake, they could then go ahead and pig out on carbs - a phenomenon which may have contributed to the current epidemic of obesity and overweight in the U.S.
The flaw in reasoning was that no one believed that the guidelines could cause any harm, therefore only the weakest evidentiary support was needed to promulgate them. Indirect evidence, expert opinions and scientific "reasoning" were the main drivers of the guidelines. After all, they were only guidelines - what could be so bad?
In fact, once published, they took on an aura of credibility that far exceeded any scientific justification. Once promulgated and given the blessing of the medical establishment and the government, they were looked upon by the public, by the media and by teachers no differently than if they had been irrefutably proven by the most rigorous scientific experimentation. And government guidelines don't simply affect one or two of us - we are all influenced by government guidelines.
The authors write that in 2000, the Dietary Guideline Advisory Committee reversed an earlier 1995 recommendation to lower fat intake, indicating that it may have been premature and ill-advised. The Committee stated that "an increasing prevalence of obesity in the United States has corresponded roughly with an absolute increase in carbohydrate consumption."
Marantz et al also point to the advice given on salt intake as another example of the unintended consequences of a seemingly innocuous recommendation, noting that any blood pressure benefits may be trumped by the stream of harmful effects on plasma renin, insulin resistance, sympathetic nerve activity, and aldosterone levels. They further point to a recent finding of no difference in total mortality between randomized sodium-intake groups.
The authors final conclusion for a dietary guideline recommendation reminded me of my dear old friend;
"When adequate evidence is not available, the best option may be to issue no guideline."
