Causes of Obesity
Obesity is a complex disease that occurs when an individual’s weight is higher than what is considered healthy for his or her height. Obesity affects children as well as adults. Many factors can contribute to excess weight gain including eating patterns, physical activity levels, and sleep routines. Social determinants of health, genetics, and taking certain medications also play a role.
Food, Activity, and Sleep
Eating and physical activity patterns, insufficient sleep and several other factors influence excess weight gain.
Social Determinants of Health (SDOH)
The conditions in which we live, learn, work, and play are called social determinants of health (SDOH). It can be difficult to make healthy food choices and get enough physical activity if these conditions do not support health. Differences in SDOH affect chronic disease outcomes and risks, including obesity, among racial, ethnic, and socioeconomic groups as well as in different geographies and among people with different physical abilities.
Places such as childcare centers, schools, or communities affect eating patterns and activity through the foods and drinks they offer and the physical activity opportunities they provide. Other community factors that influence obesity include the affordability of healthy food options, peer and social supports, marketing and promotion, and policies that determine community design.
Genetic changes in human populations occur too slowly to be responsible for the obesity epidemic. Yet variants in several genes may contribute to obesity by increasing hunger and food intake. Rarely, a specific variant of a single gene (monogenic obesity) causes a clear pattern of inherited obesity within a family., 
Illnesses and Medications
Some illnesses, such as Cushing’s disease, may lead to obesity or weight gain. Drugs such as steroids and some antidepressants may also cause weight gain. Research continues on the role of other factors such as chemical exposures and the role of the microbiome.
What Can Be Done?
- Healthy eating follows the 2020-2025 Dietary Guidelines for Americansexternal icon. It emphasizes a variety of vegetables and fruits, whole grains, a variety of lean protein foods, and low-fat and fat-free dairy products. It also limits foods and beverages with added sugars, solid fats, or sodium. See Healthy Eating for Healthy Weight.
- Managers of worksites and public facilities can improve the nutritional quality of food and beverages available in those settings. See Food Service Guidelines Implementation Toolkit.
- The Physical Activity Guidelines for Americansexternal icon recommends that children aged 3 through 5 years should be physically active throughout the day. Children aged 6 – 17 years need at least 60 minutes of moderate to vigorous physical activity every day. Adults need 150 minutes of moderate intensity physical activity a week. See Physical Activity for Different Groups.
- Communities can create or modify environments to make it easier for people to walk or bike to everyday destinations. See Community Strategies.
- Newborns need 14 to 17 hours of sleep per day. That amount decreases with age; teenagers need 8 to 10 hours of sleep per day, and adults need 7 or more hours of sleep per day. See How Much Sleep Do I Need?
Social Determinants of Health
- State early care and education systems can promote standards that address nutrition, infant feeding, physical activity, and screen time. See Early Care and Education.
- Communities, programs, initiatives, and public health practitioners can work to together to remove barriers to health and achieve health See Health Equity Resources.
- Bouchard C. Defining the genetic architecture of the predisposition to obesity: a challenging but not insurmountable taskexternal icon. Am J Clin Nutr 2010; 91:5-6.
- Choquet H, Meyre D. Genetics of obesity: what have we learned?external icon Curr Genomics. 2011;12:169-79.