Fundamentals of Human Nutrition/Defining lipids< Fundamentals of Human Nutrition
6.1 Defining lipidsEdit
As defined by Merriam-Webster - noun, concise Encyclopedia:
Any of a diverse group of organic compounds that are grouped together because they do not interact appreciably with water. One of the three large classes of substances in foods and living cells, lipids contain more than twice as much energy (calories) per unit of weight as the other two (proteins and carbohydrates). They include the fats and edible oils (e.g., butter, olive oil, corn oil), which are primarily triglycerides; phospholipids (e.g., lecithin), which are important in cell structure and metabolism; waxes of animal or plant origin; and sphingolipids, complex substances found in various tissues of the brain and nervous system. Since insolubility is the defining characteristic, cholesterol and related steroids, carotenoids (see carotene), prostaglandins, and various other compounds are also classifiable as lipids.
Lipid definition. 2013. In Merriam-Webster.com. Retrieved Jan 27, 2013, from www.merriam-webster.com/dictionary/lipid
6.1.1 Fatty acidsEdit
This section being updated by HS.
Fatty Acid Nomenclature This section being updated by SP
this section is being done by Shay Crawford
6.1.3 Phospholipids and sterolsEdit
Phospholipids resemble triglycerides in many ways, but instead of having 3 chains of fatty acids like a triglyceride, phospholipids have 2 chains of fatty acids and a chain composed of a phosphate group and a compound that contains nitrogen. In Lecithin, for instance, there are two fatty acids and then a phosphate group and a choline molecule in the third spot. Choline is a molecule the body makes from the amino acid methionine, but choline can also be obtained from food sources such as milk, eggs, peanuts, soybeans, wheat germ, and liver. The phosphate group in phospholipids is hydrophilic so it can dissolve in water, and the fatty acids in phospholipids can dissolve in fat. This makes phospholipids great emulsifiers (emulsifiers can blend water and fats). Sterols are 4-ring carbon compounds with side chains. Sterols are critical substances in the human body. Hormones that influence sex (estrogen, testosterone, etc) and the adrenal glands (such as aldosterone), Vitamin D, cholesterol, and bile acids are all sterols. Both plant and animal foods have sterols, but plant foods do not have cholesterol. Cholesterol has a 4-ring structure typical of sterols, but has carbon side chains. It can help build the cell membrane, as most of the body’s cholesterol is found there in the cell and cell membrane. Cholesterol is ideal for forming the cell membrane because of its hydrophobic and hydrophilic properties, which allow the more fluid structure of the cell membrane. Additionally, cholesterol can assist in forming hormones and bile acids. The liver produces cholesterol, so not much of it needs to be consumed through the diet. Eggs, seafood, meat, and dairy foods all have cholesterol. To keep cholesterol from being absorbed in the body, plant sterols that interfere with absorption can be added to the diet. If there is an excess build-up of cholesterol, plaque can grow within the arteries, and the body can be at a threat for atherosclerosis- a disease of the arteries that can lead to strokes and heart attack, among other health concerns. The Daily Value for cholesterol is 300 mg per day, because the liver is producing roughly 800 to 1500mg of cholesterol per day. Additional consumption of cholesterol can cause a buildup of unwanted plaque. We describe cholesterol that is consumed from our diet as exogenous, and cholesterol that is manufactured by the liver as endogenous. While they are critically important to the human body, phospholipids and sterols constitute only a small portion of the fats in our diet- around 5%.
References Berg, J., Tymoczko, J., & Stryer, L. (2002). Section 12.4, Phospholipids and Glycolipids Readily Form Bimolecular Sheets in Aqueous Media. In Biochemistry (5th ed.). New York: W H Freeman. Dietary Guidelines for Americans. (2010, December 1). Retrieved November 20, 2015, from http://www.cnpp.usda.gov/DGAs2010-DGACReport.htm Whitney, E., & Rolfes, S. (2015). Chapter 5: The Lipids: Triglycerides, Phospholipids, and Sterols. In Understanding Nutrition (14th ed.). Stamford, CT: Cengage Learning.