Although income inequality was heightened by the Great Recession and has statistically tempered, it remains a major policy concern. The outcome of research by McKinsey & Company about its cause will not please everyone. Sweet is Sweet McDonald’s, the world’s largest hamburger fast food chain, announced that it would switch from high fructose corn syrup to sugar in its hamburger buns and also stop using milk produced with rbST supplementation. It included the helpful caveat that there has been “no significant difference shown between milk from RbST-treated and non-rbST-treated cows.” The company could have added that the one scientific consensus is that over-consumption of sweeteners, whether the source is corn, beets or cane, creates...