Trans fatty acid is considered the worst type of fat there is, as it both raises your LDL cholesterol and lowers your HDL cholesterol levels. This greatly increases the risk of heart disease.  Small amounts trans fats are found naturally in some meat and dairy products, but it is mostly created in industrial processes which adds hydrogenated vegetable oils that solidifies at room temperature. This allows foods to have a longer shelf life, but is also incredibly unhealthy.