What should I know about Obesity?
Everyone knows what it means to be overweight. From early age on, children can tell the difference between "fat" and "thin" people. They also get the clear message that fat people are apt to be less popular. Body weight is one of the most basic issues of human life. Self-esteem, acceptance among peers-- and perhaps lifelong success or failure-are, unfortunately, all tied to our physical appearance.
No one wants to be fat. Thin is in, especially today. The prevalence of slender, even skinny models in advertising is ample evidence of our society's attitudes about body weight. While being overweight is certainly unhealthy, the fear and loathing attached to body fat can also be detrimental when it leads to eating disorders such as anorexia. But consternation over the impact of obsession with thinness on our national psyche, especially where young people are concerned, should not obscure the obvious fact that too many Americans are overweight. Everywhere you look, people are fighting the "Battle of the Bulge." And it is certainly a positive trend that many of us seem more health-conscious these days.
Medically speaking, not all overweight people are obese. Obesity is defined as weight that exceeds 15 percent of normal weight for height and body type. "Morbid" obesity exceeds 20 percent of optimum weight. The long-term health implications are well known, in fact, obesity is considered an outright disease. Life expectancy may be decreased in overweight and obese individuals.(1) An obese or overweight person is at high risk for a number of serious health problems, including heart disease, high blood pressure, stroke, varicose veins, dementia, psychological stress, depression, osteoarthritis, high cholesterol, and diabetes.(2),(3),(4)
The detrimental health effects of obesity are more than just a matter of weighing too much. Body composition--the amount of fat in the body compared to the amount of lean muscle--is also important.
While obesity is clearly a health threat, we should not lose sight of the fact that we need fat to stay healthy. Body fat performs many vital functions: fat provides readily accessible energy during short periods of fasting and it serves a structural component of organs, the nervous system, the brain, and muscles. We require fat in the diet to absorb the fat-soluble vitamins: vitamins A, D, E, and K.
The distribution of body weight is a key part of the equation. Excess abdominal fat in particular has been shown to increase the risk of some diseases. "Apple" shaped women--women with 30 inch or larger waists and more or less equal waist and hip measurements--appear more susceptible to heart disease and diabetes than "pear" shaped women.(5) The most harmful fat is the deep "visceral" fat that cushions the abdominal organs. Visceral fat is linked to higher levels of LDL cholesterol--the plaque-forming cholesterol--and lower levels of the good HDL cholesterol. Excess fat puts an extra burden on the liver, perhaps making it less able to metabolize cholesterol effectively.(6) Too much visceral fat also favors high blood sugar and increases the risk of diabetes.(7)
Body weight and composition are to a large degree determined by the "basal metabolic rate" (BMR), the amount of energy the body burns while at rest. The BMR is a measure of how efficiently the body converts calories into heat. It comes down to the basic laws of thermodynamics: energy consumed as calories must equal energy used up. If not, we gain weight.
Exercise is another determining factor.(8) Yes, we burn calories through physical activity. But there is more to it than that. Exercise builds lean muscle. As the ratio of lean muscle to body fat increases, so does the BMR. The higher our BMR, the more calories we burn. A safe and effective weight-loss program is one that combines calorie cutting with exercise to maintain lean muscle mass. Researchers involved in a study found that high protein diets showed comparabel, if not superior results on weight loss, preservation of lean body mass and improvement in several cardiovascular risk factors for up to 12 months as compared with lower protein diets.(9)
Body function influences body weight in other ways. Obesity can be caused by metabolic disorders of the endocrine system. The pituitary, the thyroid, and the adrenal glands all play a role in regulating metabolism. Under activity of the thyroid and pituitary can disrupt metabolic function and contribute to obesity. A disease of the adrenal glands called "Cushing's Syndrome," where the adrenals overproduce certain hormones, is another cause of obesity. High blood sugar (glucose), tissue resistance to the blood sugar-lowering effects of insulin, and impaired glucose tolerance-the characteristics of diabetes-all favor excess body fat, which in turn depresses the basal metabolic rate. Another factor is depression may lead to certain physiological changes in a person's hormone and immune system which may lead to the occurance of obesity.(10) Not getting enough sleep has been associated with weight gain. Researchers found that one hour less of total sleep time doubled the odds of a person being overweight.(11)
According to some theories, obesity may have genetic origins. This is bolstered by studies showing that two obese parents are at greater risk of having children with adult weight problems.(12) On the other hand, learned habits and poor dietary choices in childhood could have as much to do with this as heredity.(13),(14) After all, many people with overweight parents successfully manage their weight in adulthood using diet and exercise. Given the astonishing number of overweight Americans, the root causes of obesity are probably more behavioral than genetic.
Overeating and lack of exercise are the principle behavioral factors that lead to obesity. As technology and transportation dominate the 21st century, lifestyles have become increasingly sedentary.(15) Societal pressure to produce and succeed leaves less time to plan and prepare wholesome meals. Add the ever-present ads for processed, high fat, high-sugar junk foods, and it is easy to see why obesity is so commonplace. Intake of a healthy breakfast gives the body more energy and lessens the possibility of overeating or consuming unhealthy foods during the day.(16) At the same time, science is learning more about the physiology of obesity. Body fat, it has recently been discovered, contains a hormone called "leptin," that may be an internal anti-obesity factor. (17) Leptin appears to play a role in appetite control; when nerve receptors for leptin are stimulated, appetite is suppressed. A relationship has been found between obesity and a deficiency of leptin or malfunction of leptin receptors.(18) While the evidence is still preliminary, the leptin-obesity connection has been strengthened by positive results using synthetic leptin and leptin receptor-enhancing drugs on animals.(19) Researchers are also finding that overweight or obese adults and children have high levels of leptin creating leptin resistance.(20) This resistance decreases hypothalamus sensitivity to leptin which makes losing weight much more difficult and tends to actually increase the risk of gaining weight.