Final answer:
The hydrogenation of oils forms trans fats that increase 'bad' LDL cholesterol and decrease 'good' HDL cholesterol, leading to a higher risk of heart disease.
Step-by-step explanation:
The hydrogenation of vegetable oils leads to the formation of trans fats, which are known to be detrimental to human health. The process involves the addition of hydrogen to oil, converting cis-conformations to trans-conformations in the hydrocarbon chains, and thus straightening them out. These trans fatty acids increase levels of low-density lipoprotein (LDL) or 'bad' cholesterol, and decrease levels of high-density lipoprotein (HDL) or 'good' cholesterol.
Items that may contain these unhealthy fats include margarine, certain peanut butters, and shortenings. Consequently, when the chains of fatty acids straighten out due to hydrogenation, the resulting trans fats can significantly elevate the risk of heart disease by promoting the accumulation of plaque in the arteries. Acknowledging these health risks, many fast-food restaurants and food manufacturers have reduced or eliminated the use of trans fats in their products, and regulations now require trans fat content to be listed on food labels.