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Lipids: Fatty Acids, Sterols, and Triglycerides Explained

Fitday Editor

Call it fat or lipids, these terms can get confusing. But it is important to be able to differentiate them when talking about this category of nutrition. Dietary fat is a critical macronutrient, in addition to carbohydrates and protein, and there are many varieties that interact differently in the body. Fatty acids are small building blocks that create types of fat such as sterols and triglycerides. Let's take a closer look at how they all fit together to build a greater understanding of these terms in relation to our health.

Broadly, the term lipid is encompasses fats (including saturated, monoglyceride, diglyceride and triglyceride), waxes, sterols, phospholipids in the membranes of cells and fat soluble vitamins. Lipid is a basic term representing a molecule that is fat soluble (vs. water soluble). Fatty acids, sterols and triglycerides all fall under the category of lipid.

Fatty acids are the small pieces or molecules that make up the fat in our bodies and the fat we eat in our diet. Fatty acids are simply chains of carbon and hydrogen that can join together to form larger molecules such as triglycerides, sterols, saturated and unsaturated fats which will interact in our bodies. Fatty acids are building blocks. They serve as storage vehicles for energy and the body can use them easily for fuel.

Triglycerides are how the body stores energy. A triglyceride is a lipid formed from three fatty acids attached to a glycerol molecule. Triglycerides can be saturated (contain double bonds on a chemical level) and unsaturated (do not contain double bonds), meaning either solid at room temperature or liquid at room temperature due to their unique chemical structure. Saturated fats are generally found in animal food sources like meat and dairy, while unsaturated fats are found in plant food sources like olives and nuts. Triglycerides are a form of energy storage for the body and can be broken down easily for fuel. A doctor can test the triglyceride levels in your blood to be sure they are at healthy levels.

You may recognize the term sterol from the word cholesterol. A sterol is actually a subgroup of steroids that occur naturally in both plants and animals and function both as hormones as well as part of the structure in cells. Sterols are a critical part of digestion in the form of bile salts and also are found in the cell membrane, or outer wall of cells in the body. Cholesterol is a precursor of vitamin D as well. Foods known as high in dietary cholesterol include egg yolks and shrimp. Plant sterols and stanols are healthy compounds found in plant oils, nuts, seeds and legumes. Consuming plant sterols may block cholesterol from absorbing in the small intestine, helping to decrease bad cholesterol (called LDL) by about 10%. Current research shows that consuming 2-3 grams of plant sterols and stanols contribute to a healthier blood lipid profile.

A variety of healthy foods will provide you with the lipids including fatty acids, sterols and triglycerides you need for health. Fat in the diet is very dense in calories at 9 calories per gram vs. 4 calories per gram in protein and carbohydrates, so small portions of fat-containing foods contribute a lot of energy. Eating a balanced diet with different types of fat will meet your needs for energy, absorption of fat soluble vitamins, and proper cell function.


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Ginger Hultin, MS, RD, LDN is a Chicago-based dietitian who specializes in integrative oncology. With a Master's degree from naturopathic Bastyr University, she practices plant-based nutrition and specializes in lab interpretation and appropriate supplementation. Ginger also had a passion for fitness and maintains both group fitness and personal training certifications.

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