Lipids are one of the three macronutrients in your diet, along with proteins and carbohydrates, that help fuel your body and keep it functioning properly. The term "lipids" refers to fat-soluble compounds found in plants and animals. Your body uses these substances for a variety of functions, such as energy storage, absorbing fat-soluble vitamins and chemical messaging. Your body only needs a small amount of lipids, and consuming too much can cause health problems such as weight gain and high cholesterol.
Your body obtains almost all of its energy from carbohydrates and lipids. The body stores carbohydrates in the form of glycogen but can store far more lipids than carbohydrates. Carbs provide a readily available energy source, whereas your body uses lipids as energy reserve. Lipids provide 9 calories per gram, which is a little over twice as much as the energy content of carbohydrates. They play a central role in providing energy during times when food is unavailable, which isn't as much of a problem in modern times.
Insulation and Support
Lipids are stored throughout your body in connective structures called adipose tissue. They provide cushion and support to protect vital internal organs -- such as the liver, kidney, spleen and heart -- from injury. Lipids also provide thermal insulation. In addition, your body utilizes lipids to generate heat when the external temperature drops too low. This helps to keep your body warm and maintain the proper body temperature.
Absorption of Fat-Soluble Vitamins
Your body uses lipids to absorb the fat-soluble vitamins A, D, E and K from your diet. Once digested and absorbed, these vitamins are stored in your adipose tissue. This allows your body to store these vitamins for long periods of time. For this reason, your body does not need a daily supply of fat-soluble vitamins. But unlike excess water-soluble vitamins, which are excreted in urine, excess fat-soluble vitamins can cause toxicity. Eating a standard diet poses no risk, but taking high doses of fat-soluble vitamin supplements can lead to toxicity.
Lipids help maintain the structure of cell membranes and serve as chemical messengers, regulating cell function. Your body also uses lipids to form and transport cholesterol. Because lipids are not water-soluble, they travel through the bloodstream in packages called lipoproteins. Your bloodstream carries a consistent supply of lipids, and levels are higher after a meal. Having constantly elevated lipid levels in the blood is linked to an increased risk of heart disease.