Historical Overview Of Obesity
Before the dawn of industrialization, obesity was rare and admired. Until a few decades ago, only the rich had the means to become obese, and girth showed wealth and high social standing much better than expensive clothing or jewels. However, the negative health effect of obesity has always been known and well documented in literature. The term obesity was first used in medical context by a 17th century English physician named Tobias Venner. Before him, Hippocrates shrewdly observed the co-morbidity of obesity and was attributed with the quote stating "corpulence is not only a disease itself, but the harbinger of others". The biological and lifestyle causes of obesity were noted by Thomas Sydenham, another English physician of the 17th century, who stated that "corpulency may be ranked amongst the diseases arising from original imperfections in the functions of some of the organs, yet it must be admitted also, to be most intimately connected with our habits of life". In the early 1830s, the first American to associate food choices with health and morality was Reverend Sylvester Graham. He developed bland flat bread made of whole wheat flour and railed against the sin of gluttony. The Reverend was met with scorn and those who ate his Graham Cracker were regarded as “pale and sickly” while his detractors called him Dr. Sawdust!
Obesity and Adipose Tissue
Unlike explicit medical pathology with definitive diagnosis, obesity is defined by using statistical or anthropometric criteria such as body mass index (BMI). It is largely driven by chronic positive energy balance with increase in fat mass or adipose tissue. Adipose tissue is the largest organ in the human body. Unlike the heart, liver, lung or kidney, adipose tissue does not have a definitive anatomical shape. Until recently, adipose tissue was ignored and assumed to be a passive storage organ. However, unassailable evidence now points to adipose tissue as an endocrine organ actively involved in maintaining whole body health through several metabolic, hormonal and immune functions. Adipose tissue is not critical to life but lack of it (lipodystrophy) or too much of it (obesity) is critical to health because it can cause impairment in glucose and lipid homeostasis. In fact, literature now shows that adipose tissue dysfunction is the main cause of modern chronic diseases due to maladjustment between metabolic, immune and hormonal processes. Therefore, “adipose tissue failure” precedes heart, kidney, or liver failure.
Adipose Tissue Composition
Adipose tissue is a mixture of mature adipocytes and several other cells collectively referred to as stromal vascular fraction. Stromal vascular fraction consists of preadipocytes, macrophages, endothelial and mast cells. Adipocytes are not created from other adipocytes but are offshoots of precursor cells called preadipocytes. Adipocyte cells can expand (hypertrophy) when there is excess energy balance and several smaller adipocyte cells can be formed from preadipocytes (hyperplasia). Unlike other cells, adipocyte cell size can increase significantly up to 10-fold in diameter and 1000-fold in volume. The smaller and tightly packed adipocytes are typically found in the gluteo-femoral region (buttocks and thighs) and are considered metabolically healthy with anti-inflammatory properties. In adults with chronic excess energy the mature adipocytes respond by cell expansion (hypertrophy).
Metabolic Derangement of Adipose Tissue
The expansion of adipocyte cells is not limitless. Chronic expansion results in decreased oxygen supply to the adipose tissue. Low oxygen supply triggers adipose tissue to secret chemoattractants or chemokines that cause mass infiltration of blood cells called macrophages and monocytes into the tissue. Along with these immune cells, adipose tissue secretes bioactive pro-inflammatory mediators called adipokines. These adipokines coupled with accumulated intermediate metabolites of excess glucose and triglycerides result in oxidative stress and systemic low grade inflammation. Prolong low grade inflammation is associated with a metabolic dysfunction called insulin resistance, a chronic condition with elevated blood sugar levels.
Over nutrition and Target Organs
The simultaneous presence of elevated plasma concentration of glucose, free fatty acids and triglycerides affect organs in different ways. Persistent high concentrations of blood glucose puts the pancreas in overdrive with eventual death of most insulin producing cells, causing overt diabetes. Excess concentration of these nutrients and adipokines also impair endothelium, which is the inner lining of blood vessels. Impaired endothelium leads to endothelial dysfunction, atherosclerosis and hypertension. Atherosclerosis is a condition in which plaque builds up inside the arteries and limit oxygen-rich blood to parts of the body such as the heart, brain, kidneys, pelvis and legs. It may lead to cardiovascular diseases which include heart attacks, strokes, erectile dysfunction and peripheral vascular disease. Cardiovascular disease is the leading cause of death for both men and women and about 610,000 people die of heart disease in the United States annually.
Conclusion and Recommendation
Regular physical activity decreases adipocyte size and reduces lipid content causing overall decrease in adiposity. A study of Pima Indians living in Arizona and Mexico showed that Pima Indians in Arizona have a high prevalence of obesity and type II diabetes due to westernized sedentary lifestyle. On the hand, Pima Indians living a traditional lifestyle in Mexico remain lean and non-diabetic. Therefore regular physical activity is a necessary component for maintaining lipid and glucose homeostasis in any environment that enables unlimited access to consumption of excessive food. According to 2008 Physical Activity Guidelines for Americans, health benefits of physical activity occur with at least 150 mins a week of moderate-intensity aerobic activity such as brisk walking. Furthermore, everyone benefits from regular physical activity and some physical activity is better than none, even for people with disabilities. In the words of Hippocrates, “walking is man’s best medicine”.
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