Gary Taubes tells a tale of unintended consequences: When the U.S. Department of Agriculture issued the first federal dietary guidelines, it may have hoped to steer Americans away from excess fat and toward a diet of whole fruits and vegetables. But this did not happen: Overwhelmingly, Americans turned to processed, sugary, and high-carbohydrate foods instead. The result was an epidemic of obesity. Meanwhile, dietary science continued to evolve. The case against fat weakened significantly, while the case against sugar strengthened. Yet scientists do not deal in certainties; their findings come with varying degrees of confidence, a state of affairs that public policy has difficulty reflecting.

Stephan Guyenet says Americans can’t blame government nutrition advice for their overconsumption of sugar. Dietary guidelines issued in 1980 didn’t recommend substituting sugars for fats; they recommended decreasing consumption of both. Americans, however, started eating more sugar anyway. Nor is it clear that sugar is to blame for obesity, because American sugar consumption peaked in 1999 and has declined ever since. Meanwhile, obesity has continued on a steady upward trend. Sugar is one part of a larger picture that explains American obesity, diabetes, and heart disease; it is not the sole culprit.

Yoni Freedhoff says that the public policy debate about nutrition would benefit from a practical, clinical perspective. American’s eating habits have changed a lot since 1977, and while sugar is a part of that change, it’s only one part among many. Americans eat more meals outside the home. They eat more pre-packaged ready-to-eat meals. They eat larger portions. And they eat many more calories altogether. The case against fat in the 1970s and 1980s was certainly flawed, but those flaws can’t be blamed for Americans’ poor dietary choices in the meantime, and, what’s worse, today’s critics of sugar may be replicating some of the same mistakes.

Terence Kealey praises Gary Taubes for being willing to submit his nutritional theories to empirical testing. Rather than trading on influence and suspicion, Taubes has articulated a hypothesis, namely that sugar is to blame for metabolic syndrome, and he has called for further research in the area: not panic, not grandstanding, but the same sort of testing that brought us to become skeptical of earlier conclusions that have now been rejected. If the sugar hypothesis is correct, it will stand the testing. If not, it deserves to be rejected. Public health and government guidelines should wait and see, and follow the research.