How safe are fourth-generation sweeteners, such as the rare sugar allulose? First, there was sugar and high-fructose corn syrup, the original industrial sweeteners. They were cheap, but they had lots of empty calories and contributed to diseases such as obesity, type 2 diabetes, cavities, and metabolic syndrome. Then came the second-generation sweeteners, the artificial sweeteners in the colored pastel packets: NutraSweet, Splenda, and Sweet’N Low. They have practically zero calories, but there have been reports of adverse effects, prompting caution. For example, artificial sweeteners were fou...