Does 0 grams of trans fat guarantees that there are no trans fats in the food?

No, it does not. The FDA allows food products to be labeled 0 grams trans fat if there is less than 0.5 grams of trans fat. A way to double-check that there is no trans fat is by checking the ingredients list. If is says "shortening", "partially hydrogenated oils", or "hydrogenated oils", then there is trans fat in the product.