As presidential legacies go, First Lady Michelle Obama’s announcement last month of a move towards a “modernized nutrition facts label” on food products could leave a lasting impact that few other measures can match. Focusing on calories, serving sizes and sugars, it strikes a chord with a battle of the bulge that Americans have struggled with for decades — obesity, and the other complications it can bring, such as Type 2 diabetes. Nearly 800,000 products carry the label, but it has not been “significantly updated” since it was released 20 years ago, according to the White House. The benefits of such extra information on food labels are not, however, guaranteed. For one, the increased visibility of warnings about the adverse effects of unhealthy food hasn’t stopped Americans from binging on junk food. Concerns over calories, sodium and sugars have led to food makers including less of them in their products, but the evidence is thin on the gains from those actions.…