Wednesday, July 6, 2011

Lousy dietary advice? Don't blame the newspapers! Or, not only the newspapers.

All those dietary recommendations published in newspapers every day?  Anchovies are aphrodisiacs, sassafras tea cures the common cold, antioxidants prevent every known disease and will let you live forever, and so on ad infinitum.  Should we believe them?  A paper published in the journal Public Understanding of Science, and discussed on BBC radio's Material World, "The quality of the evidence for dietary advice given in UK national newspapers," takes on that question.

The authors looked at every article in every issue of the top 10 newspapers published in the UK in a random week, and assessed the quality of the health claims.
Articles, which could be features, news reports or comment pieces relating to nutrition, in the main body or in any additional supplements, were identified. Examples of article titles include: “Slimming news” and “Diet that fights kidney disease.” The criterion for inclusion was that: the article had to make a “health claim” about a food or drink which could be interpreted by the reader as advice. A health claim is defined as a “claim that states, suggests or implies that a relationship exists between a food category, a food or one of its constituents and health” (EC Regulation, 2006). For example, “red wine causes breast cancer” would constitute a dietary health claim (hereafter referred to as a “claim”) in the same way as “don’t drink red wine – it causes breast cancer” would. 

The authors then evaluated the claims by looking for supporting papers in PubMed, and graded the evidence by two different systems.  In 37 articles with dietary advice in the chosen week, there were 111 total claims, more than 3 per article on average.  Of these claims, the paper reports that 68 - 72% had no supporting evidence.  What are they teaching in journalism classes these days??

Given the extent of the obesity problem in the UK, the authors are unhappy to find that newspapers are so flippant about dietary advice.  They cite polls that show that the majority of the public believes that scientists are always changing their minds about what's true, so the best advice is to not listen to them and to eat what you want.  The authors blame this state of affairs on newspapers.

Indeed, one of the guests discussing this paper on Material World was Roger Highfield, journalist and editor of New Scientist magazine.  He wasn't at all surprised by the findings, but defended the press, saying that 'journalists are not there to issue truths, they are there to sell newspapers'.

So, there's an obesity epidemic because newspapers print irresponsible dietary advice?  Not likely. Let's agree that newspapers do print irresponsible dietary advice, but demonstrating this by weighing what's printed against scientific reports is based on an incorrect assumption that what's printed in scientific journals themselves about diet is 'true'.

As one of the co-authors of the study pointed out, dietary research is just not very rigorous.  In part this is because nutritionists haven't figured out how to credibly measure what people eat; in part it's because nutrition science is based on reducing complex foods down to single components in the lab, but it's the complex food that people eat, in combination with other complex foods, not single components; and in part it's the problem we talk about here on MT all the time -- our scientific methods aren't up to assessing complexity on its own terms.  As with genetic results, dietary results are often not replicable, or are overturned by the next big study.

So, yes, newspapers do do a lousy job of reporting dietary stories.  But, most often those stories are based on science that is confusing at best, and irresponsible at worst.

One lesson for the public (and scientists, too) is that changing our minds is exactly what science is about!  If not, everything would be known by now, and we'd be out of work.  Science has to work from, and hence to some extent 'believe in' a current explanation for things, because that is what gives us the framework for further understanding.  But it becomes our fault when we boast and trumpet too much, as we're encouraged to do by the system and by, yes, journalists who hunger for a simple story to headline. And, being only human, by taking  strong positions we back ourselves into corners that we then feel the need to defend.

The best dietary advice?  Moderation in all things.  Including what we say about those things.

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