Evidence-based diet-heart disease study a model in avoiding biased dietary recommendations
Elsewhere we cover the first rigorous examination of possible causal links between diet and heart disease . The study appeared in the April 13 edition of the American Medical Association's Annals of Internal Medicine . Its authors are with McMaster University in Hamilton, Ontario, the Canadian epicenter of "evidence-based medicine."
The authors provide context noting: "The relationship between dietary factors and coronary heart disease (CHD) has been a major focus of health research for almost a half century." The vast literature with discordant results, however, "has generated confusion among health care professionals, policy makers, and the population at large who are interested in this information to aid them in CHD prevention strategies."
The study sets the standard for evidence-based reviews and is entirely different from the approach being utilized right now by the U.S. Dietary Guidelines Advisory Committee which is utilizing the old traditional "expert panel" approach. Referencing the 2005 US Dietary Guidelines (and equally applicable to the ongoing 2010 revision process), the authors lament:
....little direct evidence from RCTs supports these recommendations. In come cases the RCTs have not been conducted, and RCTs that have been conducted have generally not been adequately powered or have evaluated surrogate end points rather than clinical outcomes. Despite this lack of information evidence-based recommendations derived from cohort studies have been advocated. This is cause for concern because dietary advice to limit the intake of a certain nutrient (i.e. dietary fat) may result in increased consumption of another (i.e. carbohydrates), which can have adverse effects on CHD risk factors. Moreover, without large prospective studies in which multiple health outcomes are evaluated, recommendations to modify a dietary component may decrease teh likelihood of one chronic disease (i.e. CHD) at the cost of increasing another (i.e. cancer)
The authors conclude that there is
strong evidence of a causal link between CHD and dietary patterns. Population-based cohort studies have demonstrated the protective effect of a quality diet against CHD and all-cause mortality. ...Dietary patterns have the advantage of taking into account the complex interactions and cumulative effects of multiple nutrients within the entire diet....
This study should become required reading for the Dietary Guidelines Advisory Committee which seems to be retreating both from objective science and transparent process. As these authors note: "Our study has a number of strengths because we undertook several measures to minimize bias" (which it proceeded to discuss). In contrast, the DGAC appointed an anti-salt zealot, a member of the rabidly anti-salt WASH advocacy group, to chair its salt subcommittee. So much for "measures to minimize bias."
Oh, and by the way, the study found
strong evidence of a causal relationship for protective factors including intake of vegetables, nuts and monounsaturated fatty acids and Mediterranean, prudent and high quality dietary patterns, and harmful factors, including intake of trans-tatty acids and foods with a high glycemic index or load and a western dietary pattern. Among these dietary exposures, however, only a Mediterranean dietary pattern has been studied in RCTs and significantly associated with CHD.
If trhat sound like what regular readers of the Salt Institute's Salt and Health newsletter have been reading about in recent years, particularly about the true nature of evidence-based reviews , how those standards are perverted in the US Dietary Guidelines process and the importance of dietary patterns , we hope that's because we, too, try to be evidence based -- but we cannot claim the exemplary rigor of these researchers who clearly practice what they preach.
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