But what the announcement really shows is how public health works: slowly, based on mounting scientific evidence, against constant and mounting headwinds of public ridicule and, much more important, industry lobbying and advertising.

Companies seldom change unless they have to, which they say means unless consumers ask them to. If you don’t want trans fats or gluten or genetically modified organisms, fine with us! Just tell us with your food dollars! This is of course a way of saying that they don’t want government telling them what to do, and gives them a chance to shape the public opinion they say they simply obey, with millions of dollars in ad campaigns and lobbying.

Just the most recent example is Tuesday’s defeat of Washington state’s Ballot Initiative 522, the latest of several statewide initiatives to require GMO labeling to fail. Here the overwhelming imbalance in campaign spending got spelled out, as Helena Bottemiller Evich at Politico and others reported, when the Grocery Manufacturers Association was forced to name the companies that had helped contributed $22 million to fight it, as opposed to the $8.4 million raised by Whole Foods, the Center for Food Safety [editor's note: an earlier version incorrectly listed CSPI as a donor], and Dr. Bronner’s, among others. The main soda makers were among the larggest donors to the anti-labeling campaign. (Even Bloomberg View is telling GMO-labeling advocates to give up and move their energies elsewhere.)

Though in my reporting I in fact frequently encounter companies that take it upon themselves to make helpful changes, for example related to environmentally and socially responsible practices, you don’t get companies to re-make their core products from scratch, risking disastrous consumer desertion sales drop-offs, unless their hands are forced. Today Olga Khazan charmingly illustrates a history of just how popular trans fats were with both manufacturers and consumers from their invention, in the early 1900s—and how they were advertised as health-promoting.

The lesson, though, is not that the public shouldn't trust science, because one year’s saturated-fats-are-evil message will eventually become next year’s hey-butter-is-great-when-you-look-at-Crisco. The road to strong public recommendations isn't clear, as scientific research is slow and zigzags. Both food makers and scientists can be guilty of jumping the gun, depending on what they think they can sell or who they can get to fund big studies and endowed chairs.

In the case of trans fats, scientific consensus about the damage they caused steadily mounted starting in the 1970s. As I wrote in an article in this magazine tracing the progress of trans fats bans, a 2002 consensus report from the National Academies of Sciences’ Institute of Medicine called the relationship between trans-fat consumption and coronary heart disease “linear,” and stated that the only acceptable level of trans fats in the diet was zero; in 2003, the Food and Drug Administration required food processors to list trans-fat levels on nutrition labels along with saturated fat. In 2006, Walter Willett, Meir Stampfer, and colleagues at the Harvard School of Public Health published a New England Journal of Medicine review article saying that trans fats caused anywhere from 72,000 to 228,000 heart-disease events a year.