Legislators potentially stall changes to dietary recommendations

An appropriations bill in the House of Representatives was passed out of the agricultural subcommittee last week.  It contained the following language:

None of the funds made available by this Act may be used to release or implement the final version of the eighth edition of the Dietary Guidelines for Americans, revised pursuant to section 301 of the National Nutrition Monitoring and Related Research Act of 1990 (7 20 U.S.C. 5341), unless the Secretary of Agriculture and the Secretary of Health and Human Services comply with each of the following requirements:
(1) Each revision to any nutritional or dietary information or guideline contained in the 2010 edition of the Dietary Guidelines for Americans and any new nutritional or dietary information or guide line to be included in the eighth edition of the Dietary Guidelines for Americans—
(A) shall be based on scientific evidence that has been rated ‘‘Grade I: Strong’’ by the 6 grading rubric developed by the Nutrition Evidence Library of the Department of Agriculture; and
(B) shall be limited in scope to only matters of diet and nutrient intake.

Not surprisingly, the move has raised the ire of some nutritionists.  Here's one who pushes back by saying

The type of studies that could produce “Grade 1: Strong” evidence is extremely difficult to do in nutrition science research, because of the realities of studying free-living human beings


It makes no sense to use different standards for existing recommendations than for new recommendations.

So, because it is too hard to get good evidence that goes beyond correlational analysis, we should be permitted to continue to use the voice of the government to promote weak evidence and advise millions of people how to eat?  And, because we've used weak science in the past, we should continue to to use it now?  

I'd ask many of these same people if drug companies should be able to get approval from the FDA for a new drug based on the same types of studies being used to make nutritional recommendations?  If the issue here is standards of scientific evidence, why the different bars of scientific scrutiny in one case vs. the other?

I'm sympathetic to the nutritionist's concerns about politics affecting science, and I don't have a position one way or the other on aforementioned language in the appropriations bill (which may or may not make into law).  Nonetheless, there is a presumption implicit in many arguments that support the recommendations that the scientists are relying on good, compelling scientific evidence.  But, they are people too, after all, as are our elected officials.  Moreover, as I've pointed out before with regard to these guidelines, there is as much value judgement going on here as there is science.  Another challenge is that the authors of the guidelines seem to presume that people will follow - precisely - the recommendations to a tee (rather than, say, substituting meat for more carbs) and will ignore cost implications, but this misses insights from behavioral research on how people will actually respond and substitute.  Most people won't follow the precise recommendations and that should be taken into consideration by the recommendation makers. The fact that we citizens are "free-living humans beings" not only makes the research hard, it should give us pause in expecting too much of high minded regulation.