What Is a Lipid?

Lipids include fats, oils, hormones, and structural molecules

A lipid is an organic molecule that can only dissolve in nonpolar solvents and will not dissolve in water. Lipids include hormones, fats, and oils and sometimes refer to fatty acids or derivatives of fatty acids. Lipids play key roles in the function of the body in both health and disease. The measurement of lipids in the blood helps determine health risks.

Low density lipoprotein in blood,
Juan Gaertner / Science Photo Library / Getty Images

Types

The three primary types of lipids are phospholipids, sterols, and triglycerides (also known as triacylglycerols). Lipids are also classified into eight categories—fatty acids, glycerolipids, glycerophospholipids, polyketides, prenols, saccharolipids, sphingolipids, and sterols.

Phospholipids

Phospholipids are major components of animal and human cells, specifically the outermost layer of these cells. They aid the maintenance of a cell’s integrity.

Phospholipids have a hydrophilic (water-loving, attracted to water molecules) portion that holds a phosphate group and a hydrophobic (water-fearing, repelled by water molecules) portion made of fatty acid derivatives. They are held together by an alcohol.

Sterols

Sterols are steroids, featuring chemical structures that are quite different from those of phospholipids and triglycerides. A sterol has a hydroxyl group on the A-ring at 3-position. This is what makes it stand out from other steroids which typically feature a structure of four fused rings.

Cholesterol is the primary steroid in the human body. When cholesterol is synthesized in the liver, it leads to many important functions including the production of hormones, vitamin D, and bile salts (compounds that help emulsify fats to be absorbed by cells).

Triglycerides

The fats and oils that you are familiar with in foods are triglycerides. A triglyceride (triacylglycerol) is an ester composed of three fatty acids bound to a glycerol. Fatty acids have different lengths of chains of hydrocarbons, from four to 36.

Triglycerides can be saturated or unsaturated, which refers to whether they have double bonds between carbon atoms (unsaturated) or not (saturated). This has a variety of effects, including whether they are liquid or solid at room temperature.

The distinction between a fat and an oil is that oils are unsaturated fats that exist in liquid form at room temperature. Most but not all unsaturated fats meet these criteria and are categorized as oils, including canola oil, corn oil, and olive oil.

Omega fatty acids are essential to the human body and must be sourced through diet such as from certain fatty fish including tuna and salmon, but also through certain nuts, seeds, and leafy vegetables. These fats reduce inflammation, blood pressure, and triglyceride levels. They reduce the risk of sudden death by a heart attack and prevent thrombosis, the formation of blood clots.

Trans fats are fats that have been artificially hydrogenated to achieve a consistency desired in processed food production. Consuming foods containing trans fats can lead to high levels of low-density lipoprotein (LDL), called "the bad cholesterol."

Function and Benefits

Lipids exist in a variety of foods and play a significant role in your diet. They’re synthesized or stored to support the cells and assist in essential processes. Lipids also have many external uses.

Cell Structure

Glycerophospholipids exist throughout the body as the primary component of the membranes surrounding every cell. They maintain the integrity of cells, and they’re found in the cell membranes of both plants and animals.

Nervous System

Lipids are integral to the nervous system found in myelin sheaths. Myelin sheaths are fatty tissue sleeves that protect your nerve cells and increase the conduction of their impulses.

Biosynthesis and Vitamin Absorption

Biosynthesis, another key function of the body, is made possible by lipids. Lipids produce the fat-soluble vitamins A, D, E and K:

  • Vitamin A is vital for your immune system and vision as well as reproduction.
  • Vitamin D aids in immune health and bone strength.
  • Vitamin E boosts the immune system, helps prevent blood clots, and safeguards cells from free radicals, functioning as an antioxidant.
  • Vitamin K aids in bone health and helps your body heal safely from injuries with the ability to form blood clots.

These are only some of the vital benefits and functions of these important vitamins. Lipids also transport and assist in the absorption of vitamins A, D, E, and K, the body’s fat-soluble vitamins.

Hormone Production

Lipids are part of the production certain hormones including estrogen, testosterone, and cortisol. These are all necessary to control your immune system and metabolism, balance your water and sodium levels, control inflammation, and aid in your physical resilience and ability to heal. These hormones also play a role in the development of sexual characteristics.

Energy Storage

Fatty acids create essential reserves of energy stored for later use.

Skin Care and Cosmetics

Lipids are used in the cosmetics industry for the production of various skin care and beauty products, such as lotions and creams. Cosmetics and skincare manufacturers add lipids to the formulations of their products for skin moisturization, protection, and repair, and for aesthetic benefits including smoother, more radiant skin with an overall improved appearance.

Pharmaceuticals

Pharmaceutical companies produce highly-beneficial, lipid-containing drug products. The drugs vary widely and include steroids (sterols) which treat diseases like cancer and regulate hormones.

Lipids are also added to certain drugs to enhance their delivery. These lipid-based drug carriers offer benefits like increased half-life, improved absorption, and the ability to target a specific area of the body with the drug.

Risks 

While lipids are essential for both adequate health and the support of your life itself (i.e. cell membrane support), excessive accumulation in the blood can put you at a high risk for the development of liver disease and cardiovascular (heart) disease.

Cardiovascular disease is the leading cause of death in the United States and across global causes of death. The World Health Organization estimates 17.9 million people die from heart disease each year, worldwide.

A buildup of low-density lipoprotein (LDL) can cause atherosclerosis (clogging of the arteries), which can lead to a heart attack or stroke. High levels of LDL can be avoided by managing cholesterol and saturated fat consumption and achieving sufficient levels of high-density lipoprotein (HDL), referred to as “good cholesterol."

Excessive LDL levels are associated with diets rich in fatty meat, fast food, deep-fried foods, milk, cheese, yogurt, butter, and processed foods. HDL-promoting foods include fish, olive oil, vegetables, legumes, nuts, and high-fiber fruits.

Lipid Panels

Your doctor may request a lipid panel as part of a routine annual physical examination or if there’s a reason to suspect certain cardiovascular diseases. Often called a cholesterol test, a lipid panel tests your blood to determine your levels of cholesterol (overall), LDL, HDL, and triglycerides.

The results help your doctor determine your risk for cardiovascular diseases and events including heart attacks and strokes.

A Word From Verywell

Lipids are macro biomolecules that are not easily dissolved in water. They have a wide range of functions within the body and diverse uses in the pharmaceutical and cosmetics industries.

While lipids provide essential functions and many health benefits, it’s important to mind the types and quantities of the lipids you consume. Not all lipids are created equal, and excessive levels of LDL poses serious risks.

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Article Sources
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