Final answer:
Partially hydrogenated vegetable oil on a cookie label indicates the presence of trans fats, which are harmful to cardiovascular health due to their effect on raising bad cholesterol (LDL) levels.
Step-by-step explanation:
The ingredient that would alert you to the presence of trans fatty acids is partially hydrogenated vegetable oil. During the partial hydrogenation process, some of the cis-C=C bonds are converted to trans-C=C bonds, leading to the production of trans fats, which are associated with negative health effects. Trans fats have been linked to an increased risk of heart disease because they raise levels of low-density lipoproteins (LDL), known as "bad" cholesterol, and contribute to plaque buildup in the arteries, which is detrimental to cardiovascular health.