Lipids are one of the key structural components of living cells, alongside carbohydrates and proteins. Many people primarily associate lipids with fats. However, a large range of organic compounds that do not dissolve in water fall under the lipid classification, including oils, waxes, hormones, and, yes, fats.

This diverse group serves a variety of functions in the body depending on their makeup and location. Storing energy, sending messages, digesting fat, and creating energy are just a few purposes of the body’s lipids.

The Four Main Classes of Lipids

Though there are many different kinds of lipids, four stand out as the most prominent: fats and oils, phospholipids, steroids, and waxes. Fat molecules, sometimes called triglycerides or triacylglycerols, store energy and consist of fatty acids and glycerol or sphingosine. Fatty acids may be saturated or unsaturated, depending on if they are “saturated” with the maximum number of hydrogen atoms.

Phospholipids are key components of cell membranes—the barrier that stops the goo-like cytosol from spilling out of the cells. Steroids help alter the permeability of the plasma membranes and transfer signals through the body. Waxes help prevent water from sticking to or soaking into a surface, such as the tops of leaves or some birds’ feathers.

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The Vital Role of Lipids in Cell Membranes

Several classes of lipids maintain or alter cell membranes. Like fats, phospholipids consist of fatty acids and glycerol but also bind to a phosphate group. Because of this, phospholipids form a bilayer that acts as the cell’s gatekeeper, maintaining structure by keeping the cell’s fluid inside and keeping other fluids outside.

Steroids, especially cholesterol, also sit within the cell membrane, performing many different jobs. Steroids are responsible for communicating with other cells and altering the cell membrane’s fluidity—basically opening the “gate” for various molecules.



Lipids as Energy Storage Molecules

The process of energy storage and fat absorption is quite complex. The summary of this process: the body stores energy as fat-containing droplets that then form adipose tissue—the visible fat around the body. This tissue undergoes constant creation and breakdown as the body stores and burns the fat for energy. Complete oxidation of fatty acids releases double the energy of carbohydrates and nearly 10 times that of proteins.

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Lipids in Hormone Production and Regulation

Hormones in the human body fall into three major groups: peptides, amines, and steroids. The steroid cholesterol is the precursor molecule for all steroid hormones, including the stress hormone cortisol, sodium-regulating aldosterone, and sex hormones like estrogen, progesterone, testosterone, and their derivatives.

Additionally, adipose tissue can secrete and produce hormones as a core part of many complex processes, such as the hormone leptin, which regulates appetite.

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Lipids and Brain Function

Lipids are incredibly important for brain function. The human brain is around 60% fat. Essential fatty acids like omega-3s are integral for brain development during fetal growth and early infancy. Even later in life, some fatty acids can help fight conditions like Alzheimer’s disease and depression.

A lack of fatty acids in the brain has links to impairment of hearing, vision, and even smell. Researchers are still uncovering the various roles and functions of lipids in the brain, but it is clear how important they are.

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Lipoproteins: Transporting Lipids in the Bloodstream

Because lipids are hydrophobic and blood is mostly water, they require assistance to travel through the body. Lipoproteins are round particles that consist of both lipids and proteins capable of moving freely in the blood.

Some lipoproteins carry cholesterol and fats from the liver to the rest of the body, and others bring cholesterol back to the liver for removal. Still others help carry oxygen and regulate inflammation.

Red blood cells and viruses in the blood stream in an artery. Eduard Muzhevskyi/ Getty Images


The Good, the Bad, and the Ugly: Cholesterol

Despite its importance in hormone creation and regulation, cholesterol also plays a potentially negative role in cardiovascular health. By measuring cholesterol-carrying lipoproteins, doctors can identify potential problems. High-density lipoprotein (HDL), also known as “good cholesterol,” carries cholesterol to the liver for removal from the body. High levels of HDL lower the risk of cardiovascular issues.

Low-density lipoprotein (LDL), the “bad cholesterol,” carries from the liver cholesterol that can accumulate in the blood vessels and cause problems. Very low-density lipoproteins (VLDL) are another type of “bad cholesterol” that transport triglycerides and cholesterol to the tissues. Intermediate-density lipoproteins (IDL) are VLDLS that give up their fatty acids. The liver either eliminates these, or they become LDLs.

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Lipids in Skin Health and Barrier Function

Human skin enables us to interact and feel the world and acts as a barrier that defends the body from pathogens and other issues. Lipids are essential to the function and structure of skin. Some lipids exist on the top layer of the skin and have antibacterial abilities. Others, such as cholesterol and ceramide, exist deeper in the skin and act as a “mortar” that holds other skin cells together and prevents water loss.

Lipid dysfunction has links to skin conditions like psoriasis, acne, and contact dermatitis.

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Lipids in the Immune System

Beyond their role in fighting pathogens in the skin, lipids also influence the immune system in other ways. The immune system defends the body by detecting, destroying, and removing pathogens. Lipid droplets in adipose tissue are often an energy source for invading pathogens, and some droplets carry proteins that attack the pathogen—like a mouse trap.

Additionally, many studies have found that a person’s diet, fat levels, and fatty acid variety can dramatically alter the immune response, often through inflammation. While more studies are necessary to fully understand these interactions, lipids clearly play a key role in how the body protects itself.

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The Future of Lipid Research

Because of their complexity, much remains unknown about lipids and their functions. Some researchers believe that understanding lipids could help fight insulin resistance and diabetes. Others believe that tracking lipids and lipoproteins will allow for faster, more accurate diagnoses of health conditions beyond cardiac issues. Some studies are even focusing on the role lipids play in the aging process and how to slow aging.

Scientists working in a laboratory. Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of ions. SolStock/ Getty Images


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