Overweight and Obesity Overweight and Obesity
Centers for Disease Control and Prevention

Is there a quick answer to the question, “what contributes to overweight and obesity?”

The obesity epidemic covered on TV and in the newspapers did not occur overnight. Obesity and overweight are chronic conditions. Overall there are a variety of factors that play a role in obesity. This makes it a complex health issue to address. This section will address how behavior, environment, and genetic factors may have an effect in causing people to be overweight and obese.

Overweight and obesity result from an energy imbalance. This involves eating too many calories and not getting enough physical activity.

Body weight is the result of genes, metabolism, behavior, environment, culture, and socioeconomic status.

Behavior and environment play a large role causing people to be overweight and obese. These are the greatest areas for prevention and treatment actions.
Adapted from U.S. Surgeon General’s Call to Action to Prevent and Decrease Overweight and Obesity, 2001

Overweight and obesity are a result of energy imbalance over a long period of time. The cause of energy imbalance for each individual may be due to a combination of several factors. Individual behaviors, environmental factors, and genetics all contribute to the complexity of the obesity epidemic.

Energy imbalance – When the number of calories consumed is not equal to the number of calories used.

Energy Balance is like a scale. When calories consumed are greater than calories used weight gain results. Weight Gain:
Calories Consumed > Calories Used
Weight Loss:
Calories Consumed < Calories Used No Weight Change:
Calories Consumed = Calories Used

“Despite obesity having strong genetic determinants, the genetic composition of the population does not change rapidly. Therefore, the large increase in . . . [obesity] must reflect major changes in non-genetic factors.”
Hill, James O., and Trowbridge, Frederick L. Childhood obesity: future directions and research priorities. Pediatrics. 1998; Supplement: 571.

Genetics and the environment may increase the risk of personal weight gain. However, the choices a person makes in eating and physical activity also contributes to overweight and obesity. Behavior can increase a person’s risk for gaining weight.

Looking back at the energy balance scale, weight gain is a result of extra calorie consumption, decreased calories used (reduced physical activity) or both. Personal choices concerning calorie consumption and physical activity can lead to energy imbalance.

Calorie Consumption
In America, a changing environment has broadened food options and eating habits. Grocery stores stock their shelves with a greater selection of products. Pre-packaged foods, fast food restaurants, and soft drinks are also more accessible. While such foods are fast and convenient they also tend to be high in fat, sugar, and calories. Choosing many foods from these areas may contribute to an excessive calorie intake. Some foods are marketed as healthy, low fat, or fat-free, but may contain more calories than the fat containing food they are designed to replace. It is important to read food labels for nutritional information and to eat in moderation.

Portion size has also increased. People may be eating more during a meal or snack because of larger portion sizes. This results in increased calorie consumption. If the body does not burn off the extra calories consumed from larger portions, fast food, or soft drinks, weight gain can occur.

How do portions today compare to portion sizes 20 years ago? The National Institutes of Health have developed a Web site with an interactive quiz called Portion Distortion! to inform people on the increasing portion sizes.

Choosing a variety of healthy foods in the correct portion sizes is helpful for achieving and maintaining a healthy weight. The Dietary Guidelines for Americans is a good resource to help people guide their dietary habits.

Calories Used
Our bodies need calories for daily functions such as breathing, digestion, and daily activities. Weight gain occurs when calories consumed exceed this need. Physical activity plays a key role in energy balance because it uses up calories consumed.

Physical activity is any bodily movement produced by skeletal muscles that results in an expenditure of energy with a range of activities such as
Occupational work
Carpentry, construction work, waiting tables, farming

Household chores
Washing floors or windows, gardening or yard work

Leisure time activities
Walking, skating, biking, swimming, playing Frisbee, dancing Structured sports or exercise Softball, tennis, football, aerobics

Regular physical activity is good for overall health. Physical activity decreases the risk for colon cancer, diabetes, and high blood pressure. It also helps to control weight, contributes to healthy bones, muscles, and joints; reduces falls among the elderly; and helps to relieve the pain of arthritis. Physical activity does not have to be strenuous to be beneficial. Moderate physical activity, such as 30 minutes of brisk walking five or more times a week, also has health benefits.

Despite all the benefits of being physically active, most Americans are sedentary. Technology has created many time and labor saving products. Some examples include cars, elevators, computers, dishwashers, and televisions. Cars are used to run short distance errands instead of people walking or riding a bicycle. As a result, these recent lifestyle changes have reduced the overall amount of energy expended in our daily lives. According to the Behavioral Risk Factor Surveillance System, in 2000 more than 26% of adults reported no leisure time physical activity.

The belief that physical activity is limited to exercise or sports, may keep people from being active. Another myth is that physical activity must be vigorous to achieve health benefits. Physical activity is any bodily movement that results in an expenditure of energy. Moderate-intensity activities such as household chores, gardening, and walking can also provide health benefits. Confidence in one’s ability to be active will help people make choices to adopt a physically active lifestyle.

People may make decisions based on their environment or community. For example, a person may choose not to walk to the store or to work because of a lack of sidewalks. Communities, homes, and workplaces can all influence people’s health decisions. Because of this influence, it is important to create environments in these locations that make it easier to engage in physical activity and to eat a healthy diet. The Surgeon General’s Call to Action to Prevent and Decrease Overweight and Obesity 2001 identified action steps for several locations that may help prevent and decrease obesity and overweight. The following table provides some examples of these steps.

Location Steps to Help Prevent and Decrease Overweight and Obesity
Home Reduce time spent watching television and in other sedentary behaviors

Build physical activity into regular routines

Schools Ensure that the school breakfast and lunch programs meet nutrition standards
Provide food options that are low in fat, calories, and added sugars
Provide all children, from prekindergarten through grade 12, with quality daily physical education

Work Create more opportunities for physical activity at work sites

Community Promote healthier choices including at least 5 servings of fruits and vegetables a day, and reasonable portion sizes
Encourage the food industry to provide reasonable food and beverage portion sizes
Encourage food outlets to increase the availability of low-calorie, nutritious food items
Create opportunities for physical activity in communities

How do genes affect obesity?

Science shows that genetics plays a role in obesity. Genes can directly cause obesity in disorders such as Bardet-Biedl syndrome and Prader-Willi syndrome.

However genes do not always predict future health. Genes and behavior may both be needed for a person to be overweight. In some cases multiple genes may increase one’s susceptibility for obesity and require outside factors; such as abundant food supply or little physical activity.

For more information on the genetics and obesity visit Obesity and Genetics: A Public Health Perspective.

Other Factors
Diseases and Drugs
Some illnesses may lead to obesity or weight gain. These may include Cushing’s disease, and polycystic ovary syndrome. Drugs such as steroids and some antidepressants may also cause weight gain.

A doctor is the best source to tell you whether illnesses, medications, or psychological factors are contributing to weight gain or making weight loss hard.