Contributing Factors

Overweight and Obesity: An Overview

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

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

The Caloric Balance Equation

When it comes to maintaining a healthy weight for a lifetime, the bottom line is — calories count! Weight management is all about balance—balancing the number of calories you consume with the number of calories your body uses or "burns off."

A calorie is defined as a unit of energy supplied by food. A calorie is a calorie regardless of its source. Whether you’re eating carbohydrates, fats, sugars, or proteins, all of them contain calories.
Caloric balance is like a scale. To remain in balance and maintain your body weight, the calories consumed (from foods) must be balanced by the calories used (in normal body functions, daily activities, and exercise).

Caloric balance is like a scale. Calories in = food and beverages. Calories out = body functions and physical activity.

If you are…	Your caloric balance status is ….
Maintaining your weight	"in balance." You are eating roughly the same number of calories that your body is using. Your weight will remain stable.
Gaining weight	"in caloric excess." You are eating more calories than your body is using. You will store these extra calories as fat and you’ll gain weight.
Losing weight	"in caloric deficit." You are eating fewer calories than you are using. Your body is pulling from its fat storage cells for energy, so your weight is decreasing.

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.

For more, see Healthy Weight – Balancing Calories.

Environment

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

Genetics

How do genes affect obesity?

"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.

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.

Related Resources

Physical Activity and Good Nutrition: Essential Elements to Prevent Chronic Disease and Obesity: At a Glance 2007

Preventing Pediatric Overweight and Obesity: AMERICAN ACADEMY OF PEDIATRICS Policy Statement*
The dramatic increase in the prevalence of childhood overweight and its health consequences are associated with significant health problems and financial burdens. This statement proposes strategies to foster prevention and early identification of overweight and obesity in children, and for dietary and physical activity interventions during physical check ups.

Understanding Adult Obesity
The National Institute of Health’s National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) created a weight-control information network. This site is an online resource for information on obesity, its causes, and health risks, and provides measurement tools and relevant publications on the topic.

Please note: Some of these publications are available for download only as *.pdf files. These files require Adobe Acrobat Reader in order to be viewed. Please review the information on downloading and using Acrobat Reader software.

* Links to non-Federal organizations found at this site are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization Web pages found at these links.

Page last reviewed: May 22, 2007
Page last updated: May 21, 2008
Content Source: Division of Nutrition, Physical Activity and Obesity, National Center for Chronic Disease Prevention and Health Promotion