Causes of Obesity
Understanding Calories and MetabolismOur bodies need calories to sustain life and be physically active. However, to maintain weight, we need to balance the energy we eat with the energy we use. When a person eats more calories than he or she burns, the energy balance is tipped toward weight gain and obesity.
This imbalance between calories-in and calories-out may differ from one person to another. Genetic, environmental, and other factors can all play a part in this imbalance. For example, we all have known someone who "could eat whatever they wanted to." In most cases, this person has been blessed with great genetics because what they burn on a daily basis (their metabolism, or "calories-out") is a lot higher than it is for the average person. There are also a number of factors that can have the opposite effect on metabolism by slowing it down, such as certain illnesses or medications.
Genetic "Causes" of ObesityOne risk factor for obesity is genetics. Obesity tends to run in families, suggesting a genetic cause. However, families also share diet and lifestyle habits that may contribute to obesity. Separating genetic influences from other risk factors for obesity is often difficult. Even so, science does show a link between obesity and heredity.
(Click Genetics and Obesity for more information.)
Environmental "Causes" of ObesityAnother risk factor for obesity is the environment, which strongly influences obesity. Most people who are alive today in the United States were also alive in 1980, when obesity rates were lower. Since this time, our genetic make-up has not changed, but our environment has.
Environment includes lifestyle behaviors, such as what a person eats and his or her level of physical activity. Too often, Americans eat out, consume large meals and high-fat foods, and put taste and convenience ahead of nutrition (see Fast Food and Obesity). Also, most people in the United States do not get enough physical activity.
Environment also includes the world around us -- our access to places to walk and healthy foods, for example. Today, more people drive long distances to work instead of walking, live in neighborhoods without sidewalks, tend to eat out or get "take out" instead of cooking, or have vending machines with high-calorie, high-fat snacks at their workplace. Our environment often does not support healthy habits.