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The 2010 Dietary Guidelines — The Best Recipe for Health?

Discussion in 'Endocrinology' started by Dr.Night, Dec 1, 2011.

  1. Dr.Night

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    The 2010 U.S. Dietary Guidelines were issued earlier this year, though they received little notice in the press. The lack of attention is troubling in a country in the throes of a nutritional crisis manifested most conspicuously in the form of an obesity epidemic that threatens to reverse recent gains in life expectancy. The current process for revising dietary guidance involves four steps: development by the Institute of Medicine (IOM) of “dietary reference intakes” (DRIs, formerly “recommended daily allowances”) for use primarily by health care professionals; formulation of recommendations, after review of relevant literature, by an expert committee appointed by the U.S. Department of Agriculture (USDA) and the Department of Health and Human Services (DHHS); creation of the official dietary guidelines in a closed-door process at the USDA with input from the DHHS; and issuance of an image depicting key messages for the public. Although the guidelines' direct educational influence is modest, they have major impact on Americans' diets, because federal food policies, including standards for schools, and many federal food-assistance programs must comply with them. The guidelines' development was carefully watched by agro-industrial interests that stand to gain or lose from their implementation.



    The new guidelines represent a mix of progress and lost opportunities. The advances include greater use of systematic reviews and increased transparency in early development stages. The guidelines appropriately emphasize eating more vegetables, beans, fruits, whole grains, and nuts and highlight healthful plant-based eating patterns, including vegetarian and vegan diets. They recommend replacing some red meat and poultry with fish, rather than simply including all these foods in the same category as other major protein sources, which vary in many ways, including fatty-acid and cholesterol content. Replacement of trans fats and saturated fats with unsaturated fats receives greater attention. Focus is placed on limiting total calorie intake instead of the proportion of calories from fat, a recommendation that we believe was never based on clear evidence. And the guidelines describe ways that physicians, organizations, and communities can act to improve people's diets and levels of physical activity; for example, physicians can help motivate Americans to prepare and consume healthful foods and advocate for healthier foods in health care facilities.



    Unfortunately, several components of the new guidelines lack scientific foundation and hinder progress. The 35% limit on calories from fat, which remains embedded deep within the document, may inadvertently undermine the quality of federally funded nutrition programs. The guidelines continue to recommend three daily servings of dairy products, despite a lack of evidence that dairy intake protects against bone fractures and probable or possible links to prostate and ovarian cancers Although eating of whole grains is encouraged, half of recommended grain intake may be in the form of refined carbohydrates, which provide many unneeded calories and cause adverse metabolic consequences. Furthermore, the quality of carbohydrates, as characterized by their glycemic index, is dismissed as unimportant, whereas we believe the evidence strongly suggests the opposite

    The new focus on reducing solid fats and added sugar (collectively referred to as “SOFAS”) could be confusing to many consumers. A clearer message would have been that Americans must reduce consumption of red meat, cheese, butter, and sugar, but that message would have offended powerful industries. Deep in the guidelines, diligent readers can find a recommendation to limit sugar-sweetened beverages, but these products deserve front-page attention as the single-greatest source of calories in the U.S. diet and an important contributor to obesity, diabetes, heart disease, gout, and dental caries. This imbalance — foods whose intake should be increased are described clearly, but those whose intake should be reduced are hidden in fine print or obscure acronyms — typifies USDA and DHHS guidelines.




    Admittedly, it's difficult to develop clear, scientifically sound guidelines. Only recently have results become available from large, long-term, prospective studies examining specific foods and clinical outcomes, and more research is needed. A focus on foods, rather than individual nutrients, is particularly important because the relationship between diet and chronic disease cannot be adequately predicted from the effects of individual nutrients, and because people choose foods, not nutrients, when deciding what to eat Moreover, the guidelines represent the assessments of a relatively small group of experts with limited time, who must summarize and interpret a vast, complex, often inconsistent, and rapidly growing body of data. In this context, prior beliefs may weigh heavily.



    Indeed, there are fundamental flaws in the process underlying guideline development, but these could largely be remedied (see Recommendations for Reforming the Process for Revising the U.S. Dietary Guidelines). Congress mandates that the dietary guidelines be revised every 5 years, a cycle that recognizes the evolving nature of science, public health issues, and the food supply. The revision includes a primary evidence review by an expert committee that is instructed to be consistent with earlier reports on DRIs from the IOM. But the IOM has no mechanism for regular review, and some nutrients haven't been examined for many years. For example, the prevailing limit on total fat consumption to 35% of calories derives from a 2002 report based on evidence purportedly linking the percentage of energy in the diet from fat with obesity. However, this relationship has since been refuted in many well-controlled, prospective, observational studies and clinical trials that show little independent effect of dietary fat on body weight. Nevertheless, the diets of millions of Americans who participate in school-lunch and nutrition-assistance programs remain loaded with refined carbohydrates in an effort to reduce fat as a proportion of total calories, whereas the focus should be on replacing trans and saturated fats with healthier fat. In addition, the recommendation to consume large amounts of dairy products follows from IOM-inspired goals for nutrient intake that may be fundamentally flawed. For example, the calcium DRI is based on measurements of calcium intake and losses in feces and urine over periods of less than 14 days, which probably don't reflect bones' long-term calcium content.5 Although DRIs warrant consideration (and periodic reassessment), recommendations regarding foods and dietary patterns should be based primarily on evidence about health outcomes, not levels of specific nutrients.



    The final step in the guideline-development process is the issuing of a graphic representation summarizing key messages. The original Food Guide Pyramid, which encouraged substituting grain products for dietary fat (irrespective of their nutritional quality), may have inadvertently contributed to epidemics of metabolic syndrome and related chronic diseases by increasing refined-starch consumption. The 2005 version, MyPyramid, conveyed little interpretable guidance about healthful food choices. The current administration, motivated by First Lady Michelle Obama's campaign against childhood obesity, has replaced MyPyramid with MyPlate. This image improves on its immediate predecessors, especially with advice to cover half the plate with vegetables and fruits. Curiously, MyPlate closely resembles the original 1940s icon, the Basic Seven — though it omits the category for “butter and fortified margarine”. However, as a representation of dietary guidelines, MyPlate is inherently constrained, most notably by failures to distinguish between whole grains and refined grain products and among protein sources, and by continued promotion of high dairy consumption.

    Although important progress has been made, Americans will need to rely on multiple sources for information about diet and health until the process of formulating the guidelines is fundamentally improved.
    [h=3]Recommendations for Reforming the Process for Revising the U.S. Dietary Guidelines.[/h] Move primary responsibility for guideline development to the CDC or IOM, to avoid conflicts of interest at the USDA arising from its institutional mission to promote commodities
    Provide the advisory committee with adequate funds to ensure a comprehensive scientific review
    Regularly update nutrient DRIs (used to inform the dietary guidelines)
    Conduct all stages of guideline development in open meetings
    Prepare public recommendations with direct input from advisory committee members
    Base recommendations primarily on foods, not nutrients
    Write guidelines that explicitly state which foods should be consumed less by Americans to reduce risk for chronic disease disclousre forms provided by the authors are available with the full text of this article at NEJM.org.




    [h=3]Source Information[/h]From the Department of Nutrition, Harvard School of Public Health (W.C.W., D.S.L.), and the Optimal Weight for Life Program, Department of Medicine, Children's Hospital (D.S.L.) — both in Boston.
     

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