The most harmful misconception about obesity is that overweight people have only themselves to blame for their extra pounds. They’re often presumed to be self-indulgent and weak-willed, which explains the lack of support and understanding accorded many large children and adults.
If overeating and under exercising were the sole causes of this chronic condition, the rate of long-term dieting success stories wouldn’t be an abysmal one in fifty. A number of factors contribute to obesity, beginning with genetic inheritance. Doctors at New York’s Columbia University College of Physicians and Surgeons studied 132 twins, aged three to seventeen. In every one of the sixty-six pairs, both youngsters had similar body-mass indexes and percentages of body fat, leading the researchers to conclude that a child’s body composition is 80 percent preprogrammed at conception.
Playing devil’s advocate for a moment, it stands to reason that twins would have similar body types. After all, they live in the same household and probably have adopted the family’s eating habits. But other studies have found that even siblings raised in different homes usually shared near-identical body mass indexes. One landmark Danish study compared the BMIs of adult adoptees with those of their birth parents and those of the couples who adopted them. Most of the adopted men’s and women’s body composition mirrored those of their biological parents, not their adoptive parents.
Heredity also determines to a large extent a person’s metabolism: the process by which the body converts the nutrients in our diet into energy (calories). The basal metabolic rate (BMR) is the pace at which we burn energy while resting. Sixty to 75 percent of our total energy is expended in this state, to maintain vital functions such as breathing, circulation, body temperature, digestion and glandular activity.
One person’s metabolic “tempo” may be as much as 20 percent faster or slower than someone else’s. That amounts to a difference of four hundred calories per day. So two teenagers can go bike riding together and eat the same number of calories, but the one with the naturally lower BMR is going to burn fewer calories. When more calories are taken in than are expended, the surplus gets stored for future use in the form of body fat. Obese adolescents frequently had lower than normal resting metabolic rates as children, before they became heavy.
Still other organic factors partly determine which kids can eat anything they want and never seem to gain an ounce, and which kids face a lifelong struggle to keep their weight in check.
Ordinarily, the hormone insulin binds to tissue cells and assists them in absorbing blood sugar (glucose), the body’s fuel. In youngsters who are resistant, the insulin fails to work effectively. Instead of being burned for energy, the sugar builds up in the body. Insulin resistance can eventually lead to noninsulin-dependent diabetes, also known as type II diabetes.
Low leptin levels.
Some people are deficient in leptin, a hormone that appears to regulate weight in two ways. The substance, produced by the fat cells, essentially signals the brain when the body has had its fill of food. It also inhibits the production of an enzyme crucial to fat production. In studies of heavy men and women, blood tests consistently revealed extremely low concentrations of leptin. The substance is currently being tested in volunteers as a potential weight-loss drug.
Chromosomal abnormalities and endocrine abnormalities.
A very few adolescents are obese due to a birth defect or a disorder of the endocrine (hormonal) system, such as hypothyroidism.