What is Fat? Lecture Based on the Work of Dr. Susan Fried
Susan K. Fried, Ph.D.
Department of Medicine, Boston University Medical School
Director, Boston Nutrition and Obesity Research Center (BNORC) (bnorc.org)
Dr. Susan Fried is one of the top experts in the study of adipose, the tissue that stores fat in specialized cells call adipocytes. For class on February 5 we reviewed two of Dr. Fried’s recent review articles on adipose tissue:
Karastergiou K, Smith SR, Greenberg AS, Fried SK. Sex differences in human adipose tissues – the biology of pear shape. Biol Sex Differ. 2012 May 31;3(1):13. doi: 10.1186/2042-6410-3-13. PubMed PMID: 22651247
Lee MJ, Wu Y, Fried SK.
Adipose tissue heterogeneity: implication of depot differences in adipose tissue for obesity complications.
Mol Aspects Med. 2013 Feb;34(1):1-11. doi: 10.1016/j.mam.2012.10.001. Epub 2012 Oct 13. Review.
People who are obese have an excess of adipose tissue, or in lay terms, too much fat.. On one hand, having excess fat is like having extra gasoline on board, and therefore, one doesn’t have to worry about running out of fuel. On the other hand, most people in our society would prefer to be thin, and too much fat predisposes people to health problems and diseases such as Type 2 diabetes and cardiovascular disease.
What is Fat?
Fat cells called adipocytes (See below) store fatty acids in the form of triacylglycerol molecules (also known as TAG), which have 3 fatty acids attached to a 3-carbon glycerol molecule. This is a safe and non-toxic way to store fatty acids, which are long hydrocarbons that are fairly similar to the hydrocarbons in gasoline.
Below is a figure that relates how much energy is stored in the body and in which form it is stored in. You can see that adipose contains most of the stored energy in the body.
From Dr. J.A. Illingworth, University of Leeds
Researchers who study fat and lipid metabolism are very interested in learning how fatty acids enter adipocytes in order to be stored as triacylglycerol molecules (fat). Likewise, researchers are interested in how fatty acids are released by adipocytes so that the fatty acids can be used by tissues such as the heart for energy. Most people would like to see some of their fat tissue disappear- especially fat that we consider in the wrong place. It turns out that fat tissues vary in the body and that the distribution of fat is vastly different between men and women. As shown in the figure below, the different distributions contribute to both body shape and to differences in the metabolism of stored fat. We will discuss these issues during class.