For now , the US government 's `` Food and Drug Administration '' has allowed makers of food products to label their products as having `` 0 grams of trans fat per serving '' as long as the amount of trans fat in the food product falls below 0.5 grams per serving . Since partially hydrogenated oils are the major source of trans fat , reading the `` ingredients '' label is the safest way to ensure that a food does not contain any trans fat at all . Products with less than 0.2 grams of trans fat per serving may be labeled as free of trans fats .