Have you heard? The GOP is declaring war on science again. In February, a government-appointed nutrition advisory panel said Americans should eat less sugar and red meat. It also suggested that environmental considerations should factor into a healthy diet, which livestock producers understood as an attack on their industry. Republicans in Congress think the guideline process is out of control and are now trying to rein in the panel. By their lights, nutrition scientists should concern themselves with nutrition -- not sustainability. Critics say they're pandering to special interests. The funny thing is: Both sides may be right. For decades,...