Science, Tech, Math › Science 10 Things You Don't Know About Fat Share Flipboard Email Print zeljkosantrac/Getty Images Science Biology Cell Biology Basics Genetics Organisms Anatomy Physiology Botany Ecology Chemistry Physics Geology Astronomy Weather & Climate By Regina Bailey Biology Expert B.A., Biology, Emory University A.S., Nursing, Chattahoochee Technical College Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in "Kaplan AP Biology" and "The Internet for Cellular and Molecular Biologists." our editorial process Regina Bailey Updated August 05, 2019 Along with proteins and carbohydrates, fat is an essential nutrient that provides energy for the body. Fat not only serves a metabolic function but also plays a structural role in the building of cell membranes. Fat is found primarily beneath the skin and is essential for maintaining healthy skin. Fat also helps to cushion and protect organs, as well as insulate the body against heat loss. While some types of fat are not healthy, others are required for good health. Discover some interesting facts you may not know about fat. 1. Fats Are Lipids but Not All Lipids Are Fats Lipids are a diverse group of biological compounds characterized generally by their insolubility in water. Major lipid groups include fats, phospholipids, steroids, and waxes. Fats, also called triglycerides, are composed of three fatty acids and glycerol. Triglycerides that are solid at room temperature are called fats, while triglycerides that are liquid at room temperature are called oils. 2. There Are Billions of Fat Cells in the Body While our genes determine the number of fat cells we are born with, newborns typically have around 5 billion fat cells. For healthy adults with normal body composition, this number ranges from 25-30 billion. Overweight adults on average can have around 80 billion fat cells and obese adults can have as many as 300 billion fat cells. 3. Whether You Eat a Low-Fat Diet or High-Fat Diet, the Percentage of Calories From Dietary Fat Consumed Is Not Linked to Disease As it relates to developing cardiovascular disease and stroke, it is the type of fat you eat not the percentage of calories from the fat that increases your risk. Saturated fats and trans fats raise LDL (low-density lipoprotein) cholesterol levels in your blood. In addition to raising LDL ("bad" cholesterol), trans fats also lower HDL ("good" cholesterol), thus increasing the risk of developing disease. Polyunsaturated and monounsaturated fats lower LDL levels and reduce the risk of disease. 4. Fat Tissue Is Composed of Adipocytes Fat tissue (adipose tissue) is composed mainly of adipocytes. Adipocytes are fat cells that contain droplets of stored fat. These cells swell or shrink depending on whether fat is being stored or used. Other types of cells that comprise adipose tissue include fibroblasts, macrophages, nerves, and endothelial cells. 5. Fat Tissue Can Be White, Brown, or Beige White adipose tissue stores fat as energy and helps to insulate the body, while brown adipose burns fat and generates heat. Beige adipose is genetically different from both brown and white adipose, but burns calories to release energy like brown adipose. Both brown and beige fat get their color from the abundance of blood vessels and the presence of iron-containing mitochondria throughout the tissue. 6. Fat Tissue Produces Hormones That Protect Against Obesity Adipose tissue acts as an endocrine organ by generating hormones that influence metabolic activity. A major function of adipose cells is to produce the hormone adiponectin, which controls fat metabolism and increases the body's sensitivity to insulin. Adiponectin helps to increase energy use in muscles without affecting appetite, to reduce body weight, and to protect against obesity. 7. Fat Cell Numbers Remain Constant in Adulthood Studies have revealed that the numbers of fat cells in adults remain constant overall. This is true regardless of whether you are lean or obese, or whether you lose or gain weight. Fat cells swell when you gain fat and shrink when you lose fat. The number of fat cells an individual has in adulthood is set during adolescence. 8. Fat Helps Vitamin Absorption Certain vitamins, including vitamins A, D, E, and K are fat-soluble and can not be properly digested without fat. Fats help these vitamins to be absorbed in the upper portion of the small intestines. 9. Fat Cells Have a 10 Year Lifespan On average, fat cells live for about 10 years before they die and are replaced. The rate at which fat is stored and removed from adipose tissue is about one and a half years for an adult with normal weight. The fat storage and removal rates balance out so that there is no net increase in fat. For an obese person, the fat removal rate decreases and the storage rate increases. The fat storage and removal rate for an obese person is two years. 10. Women Have a Higher Percentage of Body Fat Than Men Women have a greater percentage of body fat than men. Women need more body fat to maintain menstruation and also to prepare for pregnancy. A pregnant woman must store enough energy for herself and for her developing child. According to the American Council on Exercise, average women have between 25-31% body fat, while average men have between 18-24% body fat. Sources Fat turnover in obese slower than average. Lawrence Livermore National Laboratory. Published 2011 September 25. (https://www.llnl.gov/news/fat-turnover-obese-slower-average)What are the guidelines for percentage of body fat loss? The American Council on Exercise. Published 2009 December 2. (http://www.acefitness.org/acefit/healthy-living-article/60/112/what-are-the-guidelines-for-percentage-of/)Dynamics of fat cell turnover in humans. Spalding KL, Arner E, Westermark PO, Bernard S, Buchholz BA, Bergmann O, Blomqvist L, Hoffstedt J, Näslund E, Britton T, et al. Nature. 2008 Jun 5; 453(7196):783-7. Epub 2008 May 4.