CAUSES OF OBESITY

There is still an ongoing debate as to the causes of obesity.  Genetic, physiological, metabolic, environmental, psychological, and other factors may all play a part.  In the past decade, the overall prevalence of obesity has increased so that currently one-third of all Americans are obese.  Moreover, in the last twenty years, the number of obese children in the United States has doubled to one in five children.  Genetics, dietary practice, and activity level seem to all play a role in this dramatic increase.

There are additional factors that seem to play a significant role in the prevalence of obesity: sex, age, socioeconomic status, and race.  As biology only accounts for 33% of the variation in the body weight, the environment can also exert an enormous influence.  According to the centers for Disease Control, prevalence rates for obesity in women is 35% and 31% among men and is found mainly in the 20-55 age group.  Among women, obesity is strongly associated with socioeconomic status, being twice as common among those with higher status.  Although prevalence among black and white men does not differ significantly, obesity is far more common among black than among white women, affecting 60% of middle-aged black women compared with 33% of white women.

While the precise cause of obesity remains unclear, we do know that obesity is a complex condition caused by a variety of factors.  Until we are what causes obesity, it makes sense that it is difficult to develop effective ways of managing weight.

Genetic Factors

Through years of research, we do know that heredity plays a major role in the development of body size and obesity.  Based on studies comparing both identical and fraternal (no identical) twins raised together and separately, it’s evident that both environment and genetics influence obesity.  In fact, it is estimated that heredity accounts for 25% to 40% of the development of obesity.  Women have a higher percentage of body fat than do men and this seems stable across cultures and dietary habits.

There is some speculation about population differences and prevalence of obesity suggesting that some groups posses a “thrifty genotype”.  For example, the differences in diabetes and obesity in Native Americans as compared with European Americans prompted some to consider that some groups of people have survived periods of feast and famine by increased efficiency in energy storage and expenditure through a particular genotype.  However, no specific thrifty gene or genotype has been identified.

There is complex interplay of genetic factors that very likely influence the development of obesity as more than 250 genes may play a role in obesity.  There has been promising research exploring how the leptin gene influences obesity.  The leptin gene, referred to as the “fat gene” was discovered in the mid 1990s to influence satiety ot the feeling of fullness in mice.  When the leptin gene was faulty in mice, it produced lower leptin levels, and the mice experienced excessive weight gain.  However, when the leptin gene was normal, the leptin levels were higher and the mice experienced were able to maintain normal weight.  It has been theorized that leptin resistance may be involved in weight gain and the maintenance of excessive weight, but much more research needs to be conducted in this area.

Physiological and Hormonal Factors

Building on this new information about the genetic and neuropsychological basis of obesity, researchers have identified centers for the control of eating within the hypothalamus of the central nervous system (CNS).  These centers – the feeding center for hunger and the satiety center for fullness – tell the body when it should begin consuming food and when food consumption should stop.  It takes 20 minutes on average for these signals to go from the stomach to the brain to relay the message “stop eating.”

There are also hormonal factors that influence obesity.  Obesity can be caused by a condition called hypothyroidism, in which thyroid gland produces an insufficient amount of thyroxin, a hormone that regulates metabolism.  Over five million Americans have this common medical condition and as many as 10% of women may have some degree of thyroid hormone deficiency.  In such individuals, the underactive thyroid makes burning up food difficult and so weight gain is common.  As we acquire greater understanding of the hormones neuro transmitters that influence hunger and satiety, drugs designed to influence their actions will be developed.

The effects of hormonal changes on eating can be seen each month just before a woman’s menstrual cycle, as many women say that they crave salty and sugary foods during this time.  Pregnancy brings about another host of hormonal and metabolic changes.  During a normal pregnancy, a woman requires an extra 300 calories a day to support the developing fetus and supportive tissues, and to fuel her elevated maternal metabolic rate.  In addition, pregnant women will typically develop approximately 9 extra pounds of adipose tissue which will be used as an energy source during lactation.  The average woman is expected to gain between 25 to 35 pounds during pregnancy.  Many women express concern about their ability to lose this weight following the birth of the child, and some women do gain much more than the recommended amount of weight.  However, the majority of women lose their pregnancy weight within 6 months to a year after having a baby.  Nevertheless, obesity is one of the most frequent causes for complications in pregnancy.  The mother is considered obese if at the beginning of her BMI Is over 25.  Women who are obese during pregnancy have a much higher risk of hypertension and gestational diabetes.  Obesity has also been associated with infertility, poor pregnancy outcomes and miscarriage.

Typically, breast-feeding can help women to burn more calories and return to their prepregnancy weight, although extra fat may linger, as nature intended this to be a store of energy for breast-feeding.  Breast-feeding requires an additional 500 calories a day.  Mothers who breast-feed tend to lose more weight when their babies are 3 to 6 months old than formula-feeding mothers who consume fewer calories.

Metabolic Factors

Traditional theory has suggested that the energy expenditure and energy storage centers of the body possess a genetically programmed awareness of the body’s most physiologically desirable weight , called set point.  However, the term set point is somewhat misleading in that it does not refer to a certain number or point but a weight range that the body is genetically programmed maintain.  When the body falls below its natural set point, one’s metabolism reacts by slowing down the body’s functioning in order to conserve energy.  In other words, the body will sense that it is not receiving enough calories to maintain healthy functioning and so it will send calories to essential areas of the body and use the energy as efficiently as possible.  Alternatively, when someone consumes more calories than is needed, the body will begin to increase the rate of metabolism in an effort not to gain weight above the set point.  The process of storing or burning more energy to maintain the body’s “best” weight is called adaptive thermogenesis.  This process also explains the reason that 90% of people who go on any diet gain all their weight back plus more within a year of going off the diet.  When dieting, people reduce their caloric intake which in turn lowers their metabolism.  When they discontinue the diet, they typically eat more calories and foods with higher fat  content on a lowered metabolism.  This is a good formula for weight gain.  In addition, dieters tend to lose muscle and regain their weight as fat.

There is a great deal of debate on how an individual’s set point can be altered.  The number of fat cells in the body, the blood level of insulin, and regions of the brain such as the hypothalamus all seem to play a role in determining  set point.  Certain drugs such as amphetamines and other diet pills and herbal supplements can on the brain to temporarily lower the set point.  However, once these drugs are discontinued, the set point returns to the previous level or perhaps an even higher level and weight increases as a result.  Healthier and more permanent methods of changing one’s set point are through regular exercise and healthy eating patterns.  In fact, a recent study of 8,000 successful dieters found that the majority of them used “my own diet and exercise regimen” and did not follow my formal weight reduction program.

The body’s requirement for energy to maintain basic physiological processes decreases progressively with age.  This change reflects the loss of muscles tissue as both men and women age.  This loss of muscle mass eventually alters the ratio of lean body tissue to fat.  As the proportion of fat increases, the energy needs of the body are more strongly influenced by the lower metabolic needs of the fat cells.  This excess energy is then stored in the fat cells of the body.  A gradual decrease in caloric intake and a conscious effort to expend more calories can effectively prevent this gradual increase in weight leading to obesity.

Social and Cultural Factors

There are also ethnic differences related to the incidence of obesity and cultural differences regarding what is seen as a healthy weight.  African American, American Indian and Hispanic American women have the highest risk of becoming overweight, according to the Centers for Disease Control.  In fact, the results of a national study showed that more than half of all African American and Hispanic women in the United States are above what is considered a healthy body weight.  The statistics are startling: 66% of African American women, 49% are considered overweight and 24% obese.  Only one minority group, Asian Americans, has a lower rate of obesity than the general population.

Obesity is second only to tobacco as the leading cause of premature deaths and disproportionately affects women of color and women of lower socioeconomic classes.  On the positive side, African American women report less pressure to be thin than their white counterparts and tend to be less self-conscious about their weight.  Acculturation also has a significant impact on the rates of obesity – the more an ethnic group has adapted to and absorbed Western culture, the higher the rate of obesity within that group.

Socioeconomic status is also an important influence on obesity, particularly in women.  Upper socioeconomic women tend to be thinner than lower socioeconomic women, while among men there is not such a pattern.  Interestingly, higher obesity levels are also related to marriage, parenthood, and geographical location as married men, parents, and people living in rural areas tend to have a higher incidence of obesity.

Environmental Factors

Certainly environmental factors such as the smell or sight of freshly made cookies, or an advertisement for a candy bar can affect your eating habits.  Even the clock signaling it is “time to eat” can encourage us to eat even when we aren’t hungry.  While this may seem adaptive and helpful  in regulating our food intake, Dr. Kelly D. Brwonell, a professor of psychology at Yale and an expert on eating disorders, has gone so far has to label American society a “toxic environment” when it comes to food.  Researchers contend that the local environment has a powerful effect on eating.  Factors such as portion size, price, advertising, the availability of food, and the number of food choices presented all can influence the amount the average person consumes.  For example, moviegoers will eat 50% more popcorn if given an extra-large tub of popcorn instead of a container one size smaller, even if the popcorn is stale.  If a tabletop in the office is stocked with cookies and candy, co-workers tend to nibble their way through the workday, even if they are not hungry.  One study showed that when the candy was in pain sight on workers’ desks, they ate an average of nine pieces each.  Storing the candy in a desk drawer reduced to six pieces, as compared to putting the candy a couple of yards from the desk, cutting the number to three pieces per person.  In response to these and other findings, many public schools have begun offering only healthy foods in their cafeterias, replacing soft drinks, candy, and chips with juice, milk, fruit, and granola bars.

Packaging and price can also influence the amount people consume, a concept of which advertisers, restaurants, and grocery stores are well aware.  Dropping the price of the low-fat snacks by even a nickel resulted in dramatically increased sales.  In contrast, stickers signaling low-fat content or cartoons promoting the low-fat alternatives had little influence over which snacks were more popular.  This is not only true of food but also with beverages, as people tend to drink more from short, wide grasses than from thinner, taller ones, thinking they are drinking less.

Having more choices also appears to make people eat more.  In one study, people ate more when offered sandwiches with four different fillings than they did when they were given sandwiches with their single favorite filling.  In another study, participants who were a four-course meal with meat, fruit, bread, and a pudding, ate 60% more food than those served an equivalent meal of only their favorite course.  Even the cup holders in auto mobiles have grown larger to make room for giant drinks.  It is important to note that these findings were seen in people of all body sizes, not just with people who are overweight or obese as is often the misconception.  However, there does seem to be a difference in the age of the individuals studied.  One study found that 3 year old who were served three different portion sizes of macaroni and cheese for lunch on three different days ate the same amount each time.  Five-year-old, however, ate more when more was put in front of them.

Psychological Factors

Psychological factors related to overeating refer to the reasons people eat rather than due to physiological hunger.  Individuals with eating disorders often report that they don’t know when they are hungry and often eat when they are not hungry and don’t eat when they have biological reason for doing so.  Why do people eat if not in response to hunger? Frequently people eat in response to their emotions such as eating to comfort themselves, when bored, tired, stressed, or depressed.  Some people say they use food as a way of coping with hurt, sadness, and anger, suppressing their feelings and putting food on top of them.  Others eat out of habit, and associate food with certain activities such as eating popcorn at a movie, eating chips in front of the television, or having dessert after dinner.  There are certainly many associations with chocolate when feeling down as a way of cheering yourself up.  Food is also part of celebrations, holidays, family bonding, and a mainstay of socialization.  It is difficult to think about social activities we engage in that don’t involve food in some way.

Many people develop relationships with food that substitute for real human relationships.  Comments like “Food is my best friend” or “A great meal is better than sex” are indicative to the degree to which many people rely on food to fill their needs.  Psychological issues with food can become serious, even life-threatening problems.

Dietary Practices

Many researchers believe that the number of fat cells a person has will be initially determined during the first 2 years of life.  Babies who are overfed will develop a greater number of fat cells than babies who receive a balanced diet of appropriate, infant-sized portions.  When these children reach adulthood, they will have more fat cells; this increase can result in five times as many fat cells in obese people as in people of normal weight.  Dieting only reduces the size of fat cells, not the number of fat cells.  People who have an abnormally high number of fat cells are biologically limited in their ability to lose weight.

Another way people can become obese is with a pattern of overeating over a long period of time.  If an infant’s cries for food are immediately responded to, that child will be more likely to learn what the sensation of hunger is and the appropriate response.  If crying unrelated to hunger is responded to by offering a cookie or candy, that child will learn to soothe himself or herself with food.  Studies show that children become confused about what hunger is and how to satisfy it if their hunger needs are neglected or overindulged in infancy.

Some of the first power struggles between parents and their children resolve around issues of food.  A child who has little power in her life can exert power and control through her refusal to eat certain foods and demanding other foods and when she wants to eat.  Parents who use food as a reward for good behavior: “if you get an “A” on your test, I will treat you to ice cream,” as punishment: “you weren’t behaving so you can’t have dessert,” or as a guilt trip: “don’t waste food.  Clean your plate.  Children are starving in the world,” may inadvertently be creating negative dietary practice that will on throughout the child’s life.  Interestingly, research has shown that children are extraordinarily adept at meeting their nutritional needs when left to their own devices.  One study allowed children to eat whatever they wanted for a week.  Did they always pick high-fat, high-sugar foods? No.  Actually, when we look at each day’s intake, they didn’t eat a balanced diet.  However, when one takes the full week into consideration, they met their nutritional needs perfectly.

Not only does what your parents say to you have a tremendous influence on your eating behavior, but what they do themselves, their own eating practices, can have even a greater impact.  Children are exposed to different foods and model what their parents eat.  If a parent makes comments such as, Í shouldn’t eat that because I will get fat” or doesn’t et fruits or vegetables, or sits down with a bag of chips in front of the television every night, the child will probably do the same.  In the same vein, when parents exercise regularly, eat a balanced diet, and make positive comments about their weight, children tend to mimic this behavior.

Inactivity

When weight management experts are asked to identify the single most important reason that obesity is so high in today’s society, they are most certain to point to inactivity.  People of all ages tend to be less active and burn fewer calories than did their ancestors only a few generations ago.

Both adults and children spend less time devoted to exercise as a result of longer work hours at sedentary jobs, a decline in physical education programs in school, and increased participation in sedentary recreational activities, such as browsing the internet, playing video games, and watching television.  In addition, many of the laborsaving devices and increased automation in the home and workplace have contributed to increased inactivity.  According to some studies, nearly two-thirds of Americans are not physically active on a regular basis and 25% are completely sedentary.  It is not surprising that as inactivity becomes the norm, so does overweight.