Fats and cholesterol are two distinct types of lipids, which are organic compounds that are insoluble in water. Although they are often found together in food and in the blood, they have very different structures and only a few functions in common. Fats provide energy -- in calories -- but cholesterol does not. Both fats and cholesterol can be obtained in the diet and synthesized in the body, mainly the liver. Lipids, however, are absorbed together in the intestines. Because blood is mostly water, they are transported via water-soluble carrier molecules called lipoproteins.
We Need Cholesterol
Cholesterol is a waxy lipid that is present in all of our cells. Dietary cholesterol is found only in animal foods and has little effect on blood levels, according to literature reviews published in "The Proceedings of the Nutrition Society" in 2014, and "Current Opinion in Nutrition and Medical Care" in 2012. If you consume no cholesterol, your body will make what it needs. If you eat a lot of food high in cholesterol, your body makes less. Most cholesterol is produced in the liver. It is used to synthesize bile salts used for fat digestion, vitamin D, and steroid hormones, such as testosterone and estrogen. It is a component of the cell membranes and of myelin, the waxy substance that protects your nervous system.
We Need Fats, Too
Fats, and also oils, are called triglycerides, and each triglyceride contains three carbon chains called fatty acids. The kinds of fatty acids include short chain, long chain, saturated and unsaturated, which are obtained from both animal and plant foods. Most fatty acids can be metabolized for energy. Fats and oils also add flavor and satiety value to food. Sometimes fat, especially saturated fat, is confused with cholesterol. But neither one can turn into the other. Both fat and cholesterol, however, are part of the structure of the cell membrane. And some fats are part of the nervous system, alongside cholesterol.
Essential and Non-Essential Fatty Acids
The body can synthesize many fatty acids. For example, if you add a few bags of cookies to your daily diet, your body would likely turn much of it into fat and store it in your fat cells. The fatty acids we can synthesize are called "non-essential." Some fatty acids are called "essential fatty acids," which means that we must obtain them through our diet. They are also known as omega-6 and omega-3 fatty acids, which are polyunsaturated and liquid at room temperature. We need to balance them in our diet, as most types of omega-6 produces inflammation when we need it and omega-3 turns inflammation off.
Dietary cholesterol and saturated fat have been implicated in cardiovascular disease since the 1950s. Research is ongoing to re-evaluate their health risks, if any. However, one fatty acid should be avoided, and that is the industrial trans fat. This type of fat is found in partially hydrogenated vegetable oils, which is an ingredient in many processed foods, and implicated in cardiovascular and other diseases. The industrial trans fats are created in the lab and do not exist in nature. As of 2013, they were in the process of being banned in the United States. Unlike natural fats and cholesterol, they have no value in the body.
- The Proceedings of the Nutrition Society: Dietary Cholesterol, Heart Disease Risk and Cognitive Dissonance
- Current Opinion in Clinical Nutrition and Metabolic Care: Rethinking Dietary Cholesterol (2012)
- The AOCS (American Oil Chemists Society): Sterols 1. Cholesterol and Cholesterol Esters
- The Medical Biochemistry Page: Introduction to Cholesterol Metabolism
- The AOCS (American Oil Chemist Society) Lipid Library: Fatty Acids: Methylene-Interrupted Double Bonds
- New York Times: F.D.A. Ruling Would All but Eliminate Trans Fats
- Prostaglandins, Leukotrienes and Essential Fatty Acids; Function of dietary polyunsaturated fatty acids in the nervous system