What is obesity?
Obesity is defined as an excess proportion of total body fat. Nearly 60
million adults in the United States can be defined as obese. There are several
indexes used to assess obesity. The most common measure of obesity is the body
mass index (BMI).
What causes obesity?
In scientific terms, obesity occurs when a person's calorie intake exceeds
the amount of energy he or she burns. What causes this imbalance between
consuming and burning calories is unclear. Evidence suggests that obesity often
has more than one cause. Genetic, environmental, psychological, and other factors
all may play a part.
Genetic: Obesity tends to run in families, suggesting that it may have a
genetic cause. However, family members share not only genes but also diet and
lifestyle habits that may contribute to obesity. Separating these lifestyle
factors from genetic ones is often difficult. Still, growing evidence points to
heredity as a strong determining factor of obesity. In one study of adults who
were adopted as children, researchers found that their subjects' adult weights
were closer to their biological parents' weights than their adoptive parents'.
The environment provided by the adoptive family apparently had less influence on
the development of obesity than the person's genetic makeup.
Nevertheless, people who feel that their genes have doomed them to a lifetime
of obesity should take heart. As discussed in the next section, many people
genetically predisposed to obesity do not become obese or are able to lose
weight and keep it off.
Environmental factors: Although genes are an important factor in
many cases of obesity, a person's environment also plays a significant part.
Environment includes lifestyle behaviors, such as what a person eats and how
active he or she is. Americans tend to have high-fat diets, often putting taste
and convenience ahead of nutritional content when choosing meals.
While people can't change their genetic makeup, they can change what
they eat and how active they are. Some people can lose weight and keep
it off by:
- Learning how to choose more nutritious meals that are
lower in fat.
- Learning to recognize environmental cues (such as
enticing smells) that may make them want to eat when they are not
hungry.
- Becoming more physically active.
- Cutting down on portion sizes.
Psychological factors: Psychological factors also may influence
eating habits. Many people eat in response to negative emotions such as
boredom, sadness, or anger.