Lipids are the general term for fats, cholesterol, phospholipids, lipoproteins and glycolipids. It is one of the important nutrients needed by the human body. It provides the energy needed by the body and the essential fatty acids needed by the body. Lipid is one of the three nutrients that can produce energy, together with proteins and carbohydrates, and plays an important role in providing energy for the human body. It is the constituent of human cell tissue, among which phospholipids and cholesterol are the main components of all biofilms. The human body needs to absorb a certain amount of lipid substances every day, but excessive intake can lead to the occurrence and development of hyperlipidemia, atherosclerosis and other diseases. It is a compound insoluble in water but soluble in organic solvents, including fats and lipids. Fat accounts for about 15% of total human body weight, with a minimum of 13% and a maximum of 50%. Animal oils provide mainly saturated fatty acids while vegetable oils mainly unsaturated fatty acids.
The main functions of lipids are: 1. Main components of cell membrane and biofilm, fixing body tissues and organs, and fat is the isolation layer of organs and joints, filling and avoiding friction. 2. Supply and store energy. Fat intake should be 20% to 25% of total energy. One gram of fat provides 37.6 kilojoules of heat. You also need 70 to 80 grams of fat per day. 3. Promote digestion and absorption of fat-soluble vitamins.4. Maintain body temperature. Here we will introduce some important lipids below:
Phospholipids are lipids containing phosphoric acid, which are composed of glycerophospholipids and sphingolipids. Glycerophospholipids are formed by condensation of phosphoric acid and glycerol, while sphingolipids are formed by condensation of sphingosine-1-phosphate and phosphoric acid. Phospholipids mainly act as emulsifiers, meaning that a molecule of phospholipids has both a hydrophilic part bound to water and a hydrophobic part bound to oil. So, it's an intermediate medium of water and oil that doesn't blend together, and makes it work very well. Most of the phospholipids in foods are in the form of soft phospholipids. As a plant extract, phospholipids are often found in egg yolks, animal livers and legumes. Egg yolk, soybean, fish head, sesame, mushroom, yam and black fungus also contain a certain number of phospholipids.
Sphingolipids consist of a molecule of long-chain fatty acid, a molecule of sphingosine or its derivatives and a molecule of polar head alcohol. Sphingosine is the parent compound of many long chain amino alcohols in sphingolipids and is abundant in mammals. The polar head group of sphingolipids binds to the hydroxy group of sphingosines, while the fatty acid part forms amide bonds with the amino group. Therefore, sphingolipids, with a polar head group and two non-polar tails (long hydrocarbon chains of fatty acids and sphingolipids), are polar lipids, the second largest group of membrane lipids after phospholipids. Sphingolipids can be divided into sphingolipids, sphingolipids and gangliosides.
Steroids are a broad class of cyclopentane derivatives of total hydrogenation phenanthrene widely distributed in the biological world. Steroid compounds contain no bound fatty acids and are no saponifiable lipids; These compounds are isoprene like substances, which are generated by triterpene cyclization and chemical modification. Steroids include sterols (such as cholesterol, lanosterol, glusterol, soy sterol, ergosterol), bile acids and bile alcohols, steroid hormones (such as adrenocorticosteroids, androgen, estrogen), insect ecdysis hormones, cardiac glycosides, saponin ligands and bufotoxin. In addition, there are synthetic steroids such as anti-inflammatory agents (hydro prednisone, dexamethasone), steroids that promote protein synthesis and oral contraceptives. Anabolic steroids are similar to synthetic male hormones. They are a kind of synthetic chemical derivatives similar to human testosterone in structure and activity. On October 27, 2017, the world health organization's international agency for research on cancer released a preliminary list of carcinogens for reference, androgen (anabolic) steroids in the 2A list of carcinogens.