Robert Lustig is a paediatric endocrinologist at the University of California. A 90-minute talk he gave in 2009, titled Sugar: The Bitter Truth ... argues forcefully that fructose, a form of sugar ubiquitous in modern diets, is a "poison" culpable for America's obesity epidemic. John Yudkin ... was a British professor of nutrition who had sounded the alarm on sugar back in 1972, in a book called Pure, White, and Deadly. "If only a small fraction of what we know about the effects of sugar were to be revealed in relation to any other material used as a food additive," wrote Yudkin, "that material would promptly be banned." The book did well, but Yudkin paid a high price for it. Prominent nutritionists combined with the food industry to destroy his reputation. The US government issued its first Dietary Guidelines [in 1980]. The most prominent recommendation ... was to cut back on saturated fats and cholesterol. Consumers dutifully obeyed. But instead of becoming healthier, we grew fatter and sicker. Look at a graph of postwar obesity rates and it becomes clear that something changed after 1980. Just 12% of Americans were obese in 1950, 15% in 1980, 35% by 2000. Today, as nutritionists struggle to comprehend a health disaster they did not predict and may have precipitated, the field is ... edging away from prohibitions on cholesterol and fat, and hardening its warnings on sugar. But its senior members still retain a collective instinct to malign those who challenge its tattered conventional wisdom too loudly.