You may know a little about triglycerides if you've had blood work done to check your cholesterol and lipid levels, but you may not know too much about phospholipids. Although these two lipids have similar structures, they both play very different roles in your body. Knowing the differences between them may help you better understand their distinct purposes and importance to your health.
Slight Differences in Structure
If you were to see a drawing of a triglyceride molecule and a phospholipid molecule on paper, you might not be able to notice much of a difference between the two. Both molecules contain glycerol, which makes up a straight portion sometimes called a backbone, and fatty acids. These are long chains made up of hydrocarbons, and they can be either saturated or unsaturated fatty acids depending on the type of chemical bonds they contain. But a triglyceride contains three fatty acids attached to the glycerol backbone, while a phospholipid has two fatty acids plus a phosphate group attached to the glycerol. The phosphate group, a charged molecule made up of phpsohorus and oxygen, not only alters the structure of the lipid, but also its function. To get a better visual idea, a triglyceride looks like a comb with three teeth -- the fatty acids -- and a phospholipid looks like a head with two legs.
What Phospholipids Do
Because the phosphate group in the phospholipid is charged, it allows this lipid to mix with both fat and water, making it amphipathic. This is why phospholipids are able make up the outer membranes of cells. Phospholipids form a double-layer membrane -- or bilayer -- around the contents of the cell, with the phosphate heads facing both the inside and outside of the cell, and the fatty acids in rows that face each other within the membrane, helping to form a water-repelling barrier. This barrier keeps the aqueous contents of the cell separate from the aqueous exterior. However, the phospholipid membrane does allows small -- albeit important -- molecules to pass into and out of the cell, such as oxygen and carbon dioxide.
While phospholipids are important as cell membranes, that's not their only role in your body. These fats are also crucial for digestion. In the stomach, phospholipids help break fats down so they're easier to digest, and in the small intestine, the phospholipids in bile help emulsify fats so they can be carried in blood.
Role of Triglycerides
Triglycerides are the storage form of fat and make up the bulk of the lipids found in your body. This stored fat serves as an important source of energy for your body during the periods when you're not getting enough calories, such as when you're following a reduced-calorie weight-loss diet. Although you may not think of pinchable stomach fat as a good thing, this stored fat also acts as an insulator, helping keep you warm, and cushions your internal organs to protect them from injury. Triglycerides also assist in the absorption of important nutrients, such as the fat-soluble vitamins -- vitamin E, for example -- and phytochemicals like carotenoids, They also help transport them in blood and lymph to reach all your cells.
Phospholipids and Triglycerides in Food
Because your body is able to make enough on its own, phospholipids are not called essential nutrients. However, phospholipids are found in small amounts in a variety of foods, and you may consume about 2 grams a day, especially if you eat egg yolks, soy milk, tofu and peanuts, which are good sources.
Triglycerides provide 35 to 40 percent of your daily fat intake, usually from meat, milk or butter, as saturated fat, and as unsaturated fats in olive oil, nuts, seeds and salmon. Unfortunately too much fat in the diet raises triglyceride levels and leads to weight gain. Elevated blood triglyceride levels also contribute to plaque formation on your artery walls, increasing risk of atherosclerosis, which might cause serious health problems.
- Nutritional Sciences: From Fundamentals to Food; Michelle McGuire and Kathy A. Beerman
- Carnegie Melon University: Department of Biological Sciences: Introduction to Lipids
- Nutrition at a Glance; Edited by Tony Sheehy and Fariba Kolahdooz
- University of Illinois Extension: What Are Triglycerides
- Discovering Nutrition; Paul Insel, Don Ross and Melissa Bernstein,
- Nutrient Metabolism: Structures, Functions, and Genes; Martin Kohlmeier