Weighing the Evidence to Formulate Dietary Guidelines

Dietary guidelines have broad implications for the health of individuals and populations. Increasingly, government agencies and medical organization that issue guidelines have pursued evidence-based approaches. These approaches emphasize a comprehensive, critical, and explicit examination of the scientific evidence that the proposed dietary practice will improve health. Evidence-based guidelines typically feature an explicit methodology, include as their foundation a systematic review of the evidence, provide graded recommendations that are linked directly to the supporting evidence, and state explicitly when recommendations are based on opinion. Guideline development usually involves some combination of six steps: (1) specification of the topic and the guideline development methodology, (2) systematic review of the evidence, (3) consideration of expert opinion, (4) public policy analysis, (5) drafting of the document, and (6) peer review. The supporting evidence undergoes critical appraisal, including an assessment of the magnitude of the effect on outcomes observed in studies, the quality of the studies reporting the effect, or both. Dietary guidelines should also consider untoward effects, potential harms, and economic implications to society, the food industry, and others. A hallmark of evidence-based guidelines is making explicit the strength of recommendations and the quality of the evidence on which they are based. Grading systems are commonly used to rate the quality of the supporting evidence.