A fat is typically categorized as being either saturated, monounsaturated or polyunsaturated. Consumption of certain fats is actually essential to a healthy diet, others can be very harmful.
Extensive oxidation produces unhealthy by-products.
Therefore, polyunsaturated vegetable oils, such as soybean oil or sunflower oil, are poor choices when used alone for deep fat frying. To correct for the instability problems of polyunsaturated vegetable oils, the industry found a way to partially saturate the fatty acid molecules and create semi-artificial fats that are more heat stable. These changes progressively harden the fat to mimic natural saturated fats. While still a vegetable oil, PHVO provides the full amount of calories but has lost the nutrition value contained in the original vegetable oil. Federal regulations will soon require food producers to inform consumers as to the trans-fat content on the nutritional label on packages of all processed foods.