On this day, celebrated in many countries with lavish parties and high-fat foods, we’re recognizing the importance of fats in the body.

You’ve probably heard about different types of fat, such as saturated, trans, monounsaturated, omega-3, and omega-6. But fats aren’t just ingredients in food. Along with similar molecules, they fall under the broad term lipids and serve critical roles in the body. Lipids protect your vital organs. They help cells communicate. They launch chemical reactions needed for growth, immune function, and reproduction. They serve as the building blocks of your sex hormones (estrogen and testosterone).

Here we feature five of the hundreds of lipids that are essential to health.

Docosahexaenoic Acid (DHA)

DHA is an omega-3 fatty acid (known nutritionally as a “good” fat). It makes up a significant portion of the human brain, skin, sperm, testicles, and retina (part of the eye).

Although our bodies can make very small amounts of DHA, the most common source of DHA is food. Fish and seafood, particularly fatty cold-water fish such as salmon, mackerel, tuna, or herring, are the best places to find this important fat.

Sphingosine-1-Phosphate

Our bodies make sphingosine-1-phosphate by adding a few atoms to another molecule. Although we don’t need much, sphingosine-1-phosphate is necessary throughout the body. It’s especially important for shoring up the walls of blood vessels and allowing only certain molecules to enter and leave the blood stream. It protects the body from disease by directing certain immune cells to locations where they are needed to fight infection. It also has important functions in the brain and nervous system. When sphingosine-1-phosphate signaling goes awry, it can contribute to cardiovascular disease, cancer, or multiple sclerosis.

Retinal

One of many forms of vitamin A, retinal is crucial for our vision. It helps us see under low-light conditions and to recognize colors. The molecule is found in the retina, a thin cell layer at the back of the eyeball. We “see” when light enters our eyes and strikes the retina. There, retinal helps convert the light into a nerve signal. The nerve signal travels to the brain, which forms a visual image. Our bodies can make retinal from other forms of vitamin A, such as carotenes contained in carrots.

2-Arachidonoylglycerol (2AG)

2AG works as a messaging molecule in the brain and in nerve cells throughout the body. Our bodies make it, so we don’t need to get it from food. 2AG belongs to a class of nerve signaling molecules called endocannabinoids, which are similar in structure and function to the active ingredient in cannabis (marijuana). 2AG and the molecules it interacts with affect mood, memory, pain sensation, and appetite. They also are important in fertility and pregnancy. Changes in 2AG levels can contribute to many diseases, such as Alzheimer’s, multiple sclerosis, and atherosclerosis (clogging of blood vessels).

Ursodeoxycholic Acid

Bacteria in our intestines make ursodeoxycholic acid. As starting material, they use molecules known as bile acids that our bodies make in the liver, store in the gall bladder, and secrete into the intestine. Ursodeoxycholic acid helps regulate cholesterol levels. It reduces the rate at which cholesterol enters the blood from the intestine and breaks apart cholesterol clumps. Because of these effects, ursodeoxycholic acid is used as a medication to dissolve gallstones, which are rich in cholesterol. It’s also prescribed to treat certain liver diseases.

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The lipids described here are only a fraction of the hundreds found throughout the body. Researchers funded by NIGMS are studying lipids to better understand their role in normal body processes and in disease.