Every five years, the federal government (through the Departments of Agriculture and Health and Human Services) issues its “Dietary Guidelines for Americans.” The latest batch were issued in 2015, combining the usual mix of anti-steak and anti-sweets harangues, though some, including the vegan activists at Physicians Committee for Responsible Medicine (PCRM), were mildly miffed that they weren’t as aggressive as they would have liked.
But what if the evidence used to support the Guidelines were completely wrong? That’s the provocative claim made by researchers from the University of Alabama-Birmingham. The Guidelines are principally based on “memory-based dietary assessment methods”—essentially, asking people what they ate for a period of time. The problem is that people can’t remember what they ate and also make stuff up. The researchers found that somewhere between 55 and 88 percent of calorie intake estimates for the principal government dietary survey (the National Health and Nutrition Examination Survey) were “physiologically implausible” or “incompatible with life.” The team went so far as to call memory-based assessments “pseudoscientific” since the individual recall memories aren’t open to examination.
What does this all mean? There are a couple lessons we can draw. First, while the general idea that you should eat your vegetables and not eat too much are good guidance, the supposed precision of government dietary advice isn’t really all that precise. We see this all the time when “good foods” become “bad foods” and then sometimes become “good foods” again. Eggs were in, out, and are back in. Trans fats were extremely in—at the urging of the Center for Science in the Public Interest—and now they’re so out they’re basically illegal.
Secondly and most importantly, the imprecision—and potential outright wrong-ness—of the data that underlies the Guidelines means that it’s important to allow people to make their own choices on what to eat. Too many activists want to use studies based on questionable data to tax, regulate, or even ban common products. The fact that they have been badly wrong in the past should be a crucial caution when people claim they can use government policy to make us eat the “right” way.