How Evidence-Based Are New US Dietary Guidelines?

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There has long been concern that dietary guidelines are increasingly political and a new analysis contends that the U.S. Congress was right to schedule a hearing with Obama administration officials to ask why some scientific literature was included by their hand-picked group of 14 experts and why they chose to ignore data produced since the last committee met in 2010.

To the public and some policy makers, there has been concern that the guidelines are increasingly being used for social engineering food choices. For the last meeting, which completed its work in 2010, the the US Department of Agriculture (USDA) Nutrition Evidence Library (NEL) was introduced to conduct reviews. Yet the 2015 committee opted out of NEL methods for the majority of its analyses, notes journalist Nina Teicholz in BMJ. Instead, the committed relied heavily on external systematic reviews from groups such as the American Heart Association and the American College of Cardiology and critics contend their relationship with food and drug companies skews the results.

Along with external systematic reviews by advocacy groups, members conducted their own 'ad hoc' reviews of the literature without any criteria for inclusion. As is well known in scientific circles, the use of unweighted, random-effects meta-analyses in food papers has led to bizarre results, like claims that organic strawberries are somehow more "nutritious" than conventional ones. There is no evidence there were conflicts of interest but the fact that the members do not have to disclose any conflicts of interest makes policymakers and the public concerned that food choices are being slanted by groups that are chasing food fads rather than following science.

Some specific concerns:

Saturated fats: The American Council on Science and Health has long contended that a sensible diet that included saturated fats was perfectly healthy and in the last five years the rest of the nutrition community has come around to our findings that there is no causal link between saturated fats and heart disease. Yet the committee still claimed that the evidence linking consumption of saturated fats and cardiovascular disease is "strong."

Low carbohydrate diets: Numerous randomized, controlled clinical trials have found that low carbohydrate diets are valid approaches for controlling type 2 diabetes, weight loss, and improving most heart disease risk factors, but the committee did not include them.

Vegetarian bias: Instead of embracing modern studies the committee says the public needs to eat less meat and dairy and more plants - the same old low fat, high carbohydrate approach that has been shown not to work for decades.

Why not include modern reviews and the more rigorous approach put in place by the Bush administration? The committee contends that their expertise replaces systematic analysis.

"That's why you have an expert committee . . . to bring expertise," including "our own original analyses," Committee chair Barbara Millen told The BMJ.

But critics contend that the same advice for 35 years has not really helped anyone - obesity, diabetes and heart disease continued to rise. Since the committee guidelines have such an enormous impact it would also make sense to make sure that expert members are impartial, and not chosen to reflect advocacy groups.

"Growing evidence suggests that this advice is driving rather than solving the current epidemics of obesity and type 2 diabetes. The committee's conflicts of interest are also a concern. We urgently need an independent review of the evidence and new thinking about diet and its role in public health," said Dr. Fiona Godlee, The BMJ's Editor in Chief.

Citation: Nina Teicholz, 'The scientific report guiding the US dietary guidelines: is it scientific?', BMJ September 23, 2015 BMJ 2015;351:h4962