How strong is the science behind the U.S. Dietary Guidelines?

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(CNN)The U.S. Dietary Guidelines for Americansinfluence nearly every aspect of how we eat, from the information on food labels to the ingredients in school lunches to the nutrition advice doctors give.

They’re updated every five years, and new guidelines are expected this fall, after a report from the Dietary Guidelines Advisory Committee.

150728162811-small-portions-exlarge-169The committee’s leader has emphasized the importance of including only the best medical evidence and said all committee members are vetted.

But an article published Wednesday in the British Medical Journal said the report used to set the guidelines might be biased and could come from an incomplete survey of the current research.

The 2015 report “used weak scientific standards (which) seems to have made the report vulnerable to internal bias as well as outside agendas,” food journalist Nina Teicholz wrote in the British Medical Journal.

Nutrition experts said the debate likely won’t change the guidelines or the way consumers eat — but it may spark frustration as they try to get a clear answer: What does a healthy diet look like?

The research behind a healthy diet

The 2015 dietary guidelines report relied on existing reviews of the evidence base, rather than conducting original reviews, but the committee left out important studies, according to Teicholz, who wrote the book, “The Big Fat Surprise: Why Butter, Meat and Cheese Belong in a Healthy Diet.” The reviews have examined, for example, clinical trials and observational studies on whether there is a link between saturated fat consumption and heart disease and have come up with conflicting results.

The result is that the 2015 dietary guidelines report overstated the evidence for the health risks of saturated fats and understated the importance of a low-carbohydrate diet, Teicholz said. Although the recent report broke with earlier publications by exonerating cholesterol and avoiding a limit on total fats in the diet, it did state that saturated fats should not exceed 10% of total calories.

“I think (Teicholz) has really put her finger on something important here,” said Jeff Volek, a professor of human sciences at Ohio State University, who has criticized the dietary guidelines in the past. “The committee certainly missed the boat on a lot of existing data” that suggest saturated fats are not associated with heart disease and other chronic health problems, Volek said. He argued that the advisory committee didn’t give enough credit to some large analyses, as well as some of his own studies on saturated fat and heart disease.

Advice to restrict saturated fat has backfired, Volek said, because people replaced those calories with carbohydrates and sugar, and rates of obesity and diabetes in the country continue to rise. Instead, diets low in carbohydrates and without limits on saturated fats should be an option, especially for people with diabetes and prediabetes, he said. He noted that the 2015 report does include some changes he sees as positive, such as not recommending a limit on total fat.

Barbara Millen, chairwoman of the most recent advisory committee, told CNN that all of the best studies on saturated fat and carbohydrates were considered for the report. To be included, studies had to meet a long list of criteria, such as looking at health effects of dietary components over a long enough period of time.

The committee relied on existing analyses of research only if they included the most relevant studies, said Millen, who is president of Millennium Prevention, a company that develops technologies to manage diseases such as obesity, diabetes and heart disease. If not, the advisory committee commissioned its own original analyses.

Criticism of the British Medical Journal piece was published in The Verge, which said some of the studies Teicholz noted were not relevant or were outside of the purview of the report. The focus of the committee’s report, the Verge writer noted, is on maintaining health and not on preventing disease.

To read more: http://www.cnn.com/2015/09/24/health/dietary-guidelines-science/

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