Why are trans fats considered unhealthy?

Trans fats are considered unhealthy primarily because they have a detrimental effect on cholesterol levels in the body. Specifically, trans fats increase low-density lipoprotein (LDL) cholesterol, often referred to as "bad" cholesterol, while simultaneously decreasing high-density lipoprotein (HDL) cholesterol, known as "good" cholesterol. This unfavorable shift in cholesterol profiles can lead to an increased risk of cardiovascular diseases, as high levels of LDL cholesterol are associated with the buildup of plaque in arteries, ultimately contributing to heart disease and stroke.

The understanding of lipid metabolism is crucial here; maintaining a balance between LDL and HDL cholesterol is important for cardiovascular health. Trans fats do not just add to overall cholesterol levels but specifically worsen the ratio, which is a key indicator of risk for heart disease.

While other factors, such as excess calories and overall dietary patterns, can influence health, the direct impact of trans fats on cholesterol levels provides a clear mechanism through which they contribute to health risks. Thus, the emphasis on their effect on LDL and HDL cholesterol levels makes that key characteristic the reason trans fats are labeled unhealthy.