Hydrogenation adds double bonds to normally unsaturated fats, such as vegetable oils. Fully hydrogenating an oil, creating double bonds between all of the molecules in the carbon chain, turns it into a saturated fat. More commonly, oils are partially hydrogenated, creating a majority of double bonds in the fat. These partially hydrogenated oils, also known as trans fats, are more stable, spoil less easily and are solid at room temperature, but they also come with significant health effects. They are commonly used for frying, in processed foods and as margarine.

High Cholesterol and Triglycerides.

Trans fats, or partially hydrogenated oils, raise LDL cholesterol, commonly referred to as "bad" cholesterol. High LDL levels allow cholesterol to build up along the walls of arteries, creating plaques. In addition, these oils lower "good" cholesterol, or HDL, levels. Since HDL works to transport cholesterol back to the liver for processing, low levels inhibit the proper processing of cholesterol. Another effect of hydrogenated oils is to raise triglycerides, another type of lipid that can contribute to artheriosclerosis, in the bloodstream.

Cardiovascular Disease

Partially hydrogenated oils raise the risk of heart disease and mortality from heart disease. According to the Harvard School of Public Health, the risk of cardiovascular disease rises 23 percent for every 2 percent increase in calories from trans fats consumed every day. Cardiovascular disease can lead to heart attack and stroke.

Inflammation

Consumption of high levels of partially hydrogenated oils can increase inflammation in the body. In addition, they also can inhibit the enzymes necessary for reducing inflammation, compounding the effect. Inflammation within the blood vessels can trigger the buildup of plaque and damage blood vessel walls.

Brain Function

Fats are important for brain development and trans fats can crowd out the healthier essential fatty acids that the brain needs. In particular, the more hydrogenated oils a person consumes, the less DHA, a type of omega-3 fatty acid, is incorporated into neuronal cell membranes, explains the Franklin Institute. Limiting trans fats during pregnancy and breastfeeding is especially important to avoid having these fats replace DHA in the baby's developing brain. DHA may be necessary not only for the development of the fetal and infant brain, but also for preventing neurological disorders such as Alzheimer's disease and mental illnesses.

Insulin Resistance

People who eat a diet high in partially hydrogenated oils can develop an insulin sensitivity, especially if they are already prediabetic or at risk for diabetes. Insulin modulates the levels of blood glucose and a sensitivity can disrupt this process. When insulin resistance develops, the individual may not only develop diabetes, but may also have an increased risk of obesity.