Several headlines and opinion articles are written daily in most of the world’s newspapers and periodic magazines about the continuing prevalence of obesity. It is considered a chronic disease but unlike other chronic diseases such as hypertension, cancer, diabetes and heart disease, obesity prevention and control do not necessarily require a medical degree, the registered dieticians or any health professional for that matter. However, despite well-meaning unskilled advice, opinions, “guaranteed weight loss” TV commercials, diet/exercise fads and skilled medical-surgical interventions, the prevalence of obesity and its associated modern chronic diseases continue unabated in developed countries and urban centers of developing nations.
There seems to be too much emphasis on the negative cosmetic nature of weight gain with little or no understanding of functional and structural changes that occurs with an increase in fat mass (or obesity). Dysfunction of the heart, liver, lungs or kidney is often accompanied with direct treatment that targets the pathological organ to alleviate the symptoms. However, in the case of a fat mass increase, too much focus seems to be directed to the sign of obesity with little understanding of the characteristic response of fat cells to both acute and chronic conditions of overnutrition and inactivity. This article discusses the changes in structure and functions of fat cells, how fat cells affect overall health in lean and obese states, and ways to reduce excessive weoht gain.
Fat or adipose tissue is made of multiple specialized cells that include white fat cells, brown fat cells, and other cells such as precursor cells or preadipocytes, endothelial cells, and macrophages which are collectively referred to as stromal vascular fraction. The white fat cells or white adipocytes constitute the largest percentage of fatty tissue and it’s the principal focus of this post and would simply be referred to as fat cells.
Fat cells store energy in form of triglycerides. They have the quick flexibility to give off these substrates, in form of free fatty acids, to distant organs upon nutritional demand during fasting or increased energy need from physical exercise. Just like glucose, excessive concentration of fats or lipids inside the cells or on the lining of blood vessels is very toxic. For this reason, fats cells are uniquely able to pick up free fatty acids from the bloodstream, convert them to inert or non-corrosive triglycerides (lipogenesis) and store them away in lipid droplets. The lipid droplet is a subcellular fat storage compartment within each fat cell which helps protect fat cells and distant organs such as muscles and pancreas from toxic exposure to free fatty acids (lipotoxicity). Additionally, lipid droplet can expand up to 100 micrometers or more in diameter and largely responsible for the characteristic adipose or fat tissue expansion in response to acute or chronic overnutrition. The specialized membrane (perilipin) of the lipid droplet helps to keep triglycerides sequestrated from hormone sensitive lipase, an enzyme which acts to break them into free fatty acids and glycerol (lipolysis). There are two ways to gain weight or increase fat mass in response to sustained positive energy balance:
1. the existing fat cells can expand (hypertrophy)
2. the preadipocytes can form new mature fat cells by increasing the number of fat cells (hyperplasia) in a process called adipogenesis.