Many people have heard of hydrogenated oils, but may not fully understand them. Basically, hydrogenation is the process of making a liquid a solid. When liquid vegetable oils are converted into solid fats, such as vegetable shortening or margarine, hydrogenated fats, also known as trans fats, are the result.
These fats have been used in food production for nearly a century because they improve shelf life and stability. The most common sources of these oils are probably going to be anything containing vegetable shortening (pastries, desserts, etc.), stick margarines and some tub margarines, peanut butter, frosting, crackers, salad dressings, and more.
While food companies have been required to put trans fat content on the Nutrition Facts labels of their products since 2006, they are still allowed to list trans fat contents as 0g if there is 0.5g or less or trans fat in the food. For example, if you come across a food with 0g trans fat listed on the label, but you see “partially hydrogenated oil” listed in the ingredients, there will be some trans fat in that product, but less than 0.5g per serving.
Many food companies are attempting to limit their use of these fats in their products. Unfortunately, they tend to substitute for these fats with saturated fat, which is not necessarily a healthy alternative. Watch out for higher saturated fat contents in foods advertised as having “No Trans Fats “ or “No Hydrogenated Oils.”
Current recommendations are to limit daily trans fat intake to 2g or less because of negative effects on heart health. Including increased LDL (bad) levels and lowered HDL (good) cholesterol levels.
For more information on hydrogenated oils, check out this great handout from Penn State.