In the simplest sense, weight gain and obesity result from an imbalance of calories and energy over time. However, there are many more factors that contribute to obesity than simply consuming more calories than are burned. From genetic predisposition to various lifestyle choices, there are numerous complex issues to address when thinking about the causes of obesity. While each individual will have a different story to tell, the following descriptions represent the most common contributing factors for obesity in today's society.

Genetics Recent studies have shown that genetics is an important contributing factor for obesity. However, while there are certain genetic conditions that can lead to obesity regardless of behavior, most often genes merely increase the susceptibility for obesity. Hence, if an individual possesses genes that increase the chances of becoming obese, other factors such as a poor diet or a lack of physical activity will also contribute to the condition.

Metabolic Rate When the body is in a relaxed state, internal organs burn calories naturally as they require energy to function. Known as the resting metabolic rate, this calorie burn is fueled in large part by muscle mass. However, as people grow older and their muscle mass decreases, the body's metabolic rate follows suit, making it easier to gain weight. As fat replaces muscle in the body, the effects on metabolism are staggering. In fact, some studies have shown that the loss of a single pound of muscle can cause the resting metabolic rate to drop by 50 calories per day. When considering that each pound of fat replacing the lost muscle burns only 2 calories each day, it is easy to see why losing weight can be so difficult when overweight or obese.

Diet As metabolism slows with age and development of excess fat, a high-calorie diet can become a dangerous contributing factor for obesity. Regular consumption of high-fat, high-calorie foods - including many fast food items, soft drinks and desserts - can expedite weight gain and jeopardize the body's overall health by increasing LDL cholesterol and risk of heart disease. Furthermore, as portion sizes continue to grow at restaurants across the country, many seemingly 'healthy' meals can also pack a dangerous amount of calories and cause significant weight gain.

Physical Lifestyle Much as a poor diet can cause an individual to consume too many calories, a lack of physical activity prevents many of those calories from being used. As mentioned, when the body consumes more calories than it burns, weight is gained. While the body burns some calories throughout the day regardless of physical activity, it can be very difficult to maintain a healthy body weight without regular movement and exercise. Furthermore, as technology and other modern conveniences have reduced the amount of physical activity in daily life, it has become increasingly important for families to set aside time for sports, active hobbies or other calorie-burning activities.

Culture and Environment As so many Americans rely on automobiles to travel even the shortest distances and time-saving technology to complete formerly active chores, modern culture has had a dramatic impact on obesity rates. Furthermore, many Americans now reside in communities that are not pedestrian-friendly, while many current jobs emphasize working at a computer rather than mobility. Short on time and resources, such people often overlook physical activity and healthy eating. Yet, many people don't realize that an extra 20-30 minutes of brisk walking or substituting healthier foods into an everyday diet can drastically improve overall health and help prevent obesity.

Emotional or Psychological Factors Individuals living unhealthy lifestyles that incorporate high-calorie diets and avoid regular physical activity can also suffer from emotional or psychological problems. Whether the issues stem from anxiety about a hectic lifestyle or a constant struggle with weight gain, such emotional difficulties often make it more difficult to affect healthy changes in everyday life. When the psychological problems are more serious, conditions such as depression can contribute directly to overeating, lack of physical activity and potentially obesity.

Medical Problems In some cases, obesity can develop as a result of other medical conditions. For instance, individuals suffering from low thyroid function or Cushing's syndrome - an ailment caused by excess hormone production in the adrenal glands - may be at greater risk of developing obesity. Additionally, arthritis and other conditions that limit mobility and physical activity can contribute to weight gain and obesity.

Though there are some contributing factors that cannot be avoided - such as genetics and preexisting medical conditions - most of the issues discussed here can be positively impacted by making healthy lifestyle choices. Yet, while individuals that don't suffer from obesity may experience successful weight loss by eating smaller portions and maintaining physical activity, those that are severely obese may need to consider weight loss surgery to reverse the effects of these factors. Weight-loss surgery can give patients the necessary tools to make such healthy changes, experience long-term weight loss and overcome some of the most challenging causes of obesity.