Development Of Obesity

The body consists of 30 to 40 billion adipose cells (fat cells) that provide storage space for extra energy. Adipose cells may be viewed as collapsible, thin ­ walled containers with unlimited storage capacities. In prehistoric times large fat stores developed when food was available in spring and summer, and this proved biologically advantageous when winters were long and harsh and food was scarce. Energy stored in fat cells could be tapped for use later. This is not the case today. Food is available year-round for most Americans and addition to food stores rather than maintenance is not advantageous.nnObesity occurs when adipose cells increase excessively in size (hypertrophy) and/or number (hyperplasia). Obesity that results from an increase in the size of fat cells is hypertrophic, obesity that results from an increase in the number of fat cells is hyperplastic, and obesity that results from an increase in both is hypertrophic/hyperplastic.nnAdipose cells follow a normal pattern of growth and development. When obesity develops in infancy or childhood the person develops more adipose cells and each cell grows greatly, resulting in hypertrophic/hyperplastic obesity. When obesity develops in adulthood (adult onset obesity), the person usually ends up with a normal number of adipose cells, but each cell contains a large amount of fat . In extreme cases adult-onset obesity can be both hyperplastic and hypertrophic. Once developed, fat cells do not disappear in the adult state.nnAdipose cells have a long life span. If adult obesity is both hypertrophic and hyperplastic, is it more difficult to lose weight than if adult obesity is due to hypertrophy alone? Some evidence indicates that an increased number of fat cells increases the body's reluctance to reduce fat stores. The needs of adipose cells may require that they store at least nominal amounts of fat. More fat cells would then result in more fat storage, complicating efforts to lose weight. The longer a person remains obese, the more difficult it is to correct the problem.nnGender differences in depositing fat become noticeable during and after puberty. Men distribute fat primarily in the upper half of the body, and women tend to deposit it in the lower half. The percentage of fat in the body reaches peak values during early adolescence for boys and then declines during the remainder of adolescent growth. Girls experience a continuous increase in the percentage of fat from the onset of puberty to age.nnFrom approximately 2 years of age, obese children develop a greater number of fat cells than children of normal weight, often as many as three times more. Although it is widely believed that obese children become obese adults, only about one third of obese preschoolers become obese adults. However, the risk of adult obesity is greater for children and young adults who are obese at older ages. One half of obese school age children become obese adults, and more than 80% of obese adolescents become obese adults. Although these percentages are high, it should be remembered that the cohort of obese children represents one fourth of all children and therefore does not account for the larger percent of obese adults. Approximately 80% to 90% of obesity is thought to be adult onset.