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The scientific report guiding the US dietary guidelines: is it scientific? The British Medical Journal says “No.”

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As scientists understand better what happens from our dietary choices, those creating the US government’s dietary guidelines ignore the findings. Nina Teicholz reports in the British Medical Journal (and there is also a 15-minute audio at the link):

The expert report underpinning the next set of US Dietary Guidelines for Americans fails to reflect much relevant scientific literature in its reviews of crucial topics and therefore risks giving a misleading picture, an investigation byThe BMJ has found. The omissions seem to suggest a reluctance by the committee behind the report to consider any evidence that contradicts the last 35 years of nutritional advice.

Issued once every five years, the guidelines have a big influence on diet in the US, determining nutrition education, food labeling, government research priorities at the National Institutes of Health, and public feeding programs, which are used by about a quarter of Americans each year.1 The guidelines, which were first issued in 1980, have also driven nutrition policy globally, with most Western nations subsequently adopting similar advice.

The guidelines are based on a report produced by a dietary guidelines advisory committee—a group of 11-15 experts who are appointed to review the best and most current science to make nutrition recommendations that both promote health and fight disease. The committee’s latest report was published in February2 and is under review by the government’s health and agricultural agencies, which will finalize the guidelines in the fall.

Concern about this year’s report has been unprecedented, with some 29 000 public comments submitted compared with only 2000 in 2010. In recent months, as government officials convert the scientific report into the guidelines, Congress has sought to intervene. In June, it proposed a requirement that the guidelines be based exclusively on “strong” science and also that they focus on nutritional concerns without consideration of sustainability. Other debated topics include newly proposed reductions in consumption of sugar and red meat.

These issues will likely come to a head at a Congressional hearing on the guidelines in October, when two cabinet secretaries are scheduled to testify.

The BMJ has also found that the committee’s report used weak scientific standards, reversing recent efforts by the government to strengthen the scientific review process. This backsliding seems to have made the report vulnerable to internal bias as well as outside agendas.

The 2015 report states that the committee abandoned established methods for most of its analyses. Since its inception, the guideline process has suffered from a lack of rigorous methods for reviewing the science on nutrition and disease, but a major effort was undertaken in 2010 to implement systematic reviews of studies to bring scientific rigor and transparency to the review process. The US Department of Agriculture set up the Nutrition Evidence Library (NEL) to help conduct systematic reviews using a standardized process for identifying, selecting, and evaluating relevant studies.3

However, in its 2015 report the committee stated that it did not use NEL reviews for more than 70% of the topics, including some of the most controversial issues in nutrition.4 Instead, it relied on systematic reviews by external professional associations, almost exclusively the American Heart Association (AHA) and the American College of Cardiology (ACC), or conducted an hoc examination of the scientific literature without well defined systematic criteria for how studies or outside review papers were identified, selected, or evaluated.

Use of external reviews by professional associations is problematic because these groups conduct literature reviews according to different standards and are supported by food and drug companies. The ACC reports receiving 38% of its revenue from industry in 2012, and the AHA reported 20% of revenue from industry in 2014. Potential conflicts of interest include, for instance, decades of support from vegetable oil manufacturers, whose products the AHA has long promoted for cardiovascular health. This reliance on industry backed groups clearly undermines the credibility of the government report.

Saturated fats

On saturated fats, for example, . . .

Continue reading. There’s a lot more. On low-carb diets, for example:

Low carbohydrate diets

Another important topic that was insufficiently reviewed is the efficacy of low carbohydrate diets. Again, the 2015 committee did not request a NEL systematic review of the literature from the past five years. The report says that this was because, after conducting “exploratory searches” of the literature since 2000, the committee could find “only limited evidence [on] low-carbohydrate diets and health, particularly evidence derived from US based populations.”27

The report provides no documentation of these “exploratory searches,” yet many studies of carbohydrate restriction have been published in peer review journals since 2000, nearly all of which were in US populations. These include nine pilot studies, 11 case studies, 19 observational studies, and at least 74 randomised controlled trials, 32 of which lasted six months or longer (see table C on thebmj.com). A meta-analysis and a critical review have concluded that low carbohydrate diets are better than other nutritional approaches for controlling type 2 diabetes,28 29 and two meta-analyses have concluded that a moderate to strict low carbohydrate diet is highly effective for achieving weight loss and improving most heart disease risk factors in the short term (six months).30 31Weight loss benefits on different diets tended to converge over the long term (12 months), according to various reviews, but a recent meta-analysis found that if carbohydrates are kept “very low,” weight loss is greater than with a low fat diet maintained for a year.32 Given the growing toll taken by these conditions and the failure of existing strategies to make meaningful progress in fighting obesity and diabetes to date, one might expect the guideline committee to welcome any new, promising dietary strategies. It is thus surprising that the studies listed above were considered insufficient to warrant a review.

Written by LeisureGuy

30 September 2015 at 10:27 am

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