Trans Fat Truth in Labeling Act of 2013 - Directs the Commissioner of Food and Drugs (FDA) to promulgate a final regulation revising federal nutrition labeling regulations to: (1) require the label of a food that has less than 0.5 grams and greater than 0.0 grams of trans fat per serving to contain an asterisk or other notation and a note that the food has a low trans fat content per serving, and (2) prohibit the label or labeling on such a food from indicating that the trans fat content per serving is zero.