Overweight and Obesity
Overweight and Obesity

Overweight and Obesity Causes and Risk Factors

What causes overweight and obesity?

Overweight and obesity can develop over time when you consume more calories than you use. This is also described as an energy imbalance: when your energy in (calories) does not equal your energy out (calories your body uses for things such as breathing, digesting food, and being physically active).

Your body uses certain nutrients, such as carbohydrates or sugars, proteins, and fats, from the foods you eat to make and store energy.

  • Food is turned into energy for immediate use to power routine daily body functions and physical activity.
  • Food is stored as energy for future use by your body. Sugars are stored as glycogen in the liver and muscles. Fats are stored mainly as triglycerides in fatty tissue.

An energy imbalance causes your body to store more fat than can be used now or in the future. But your risk of developing overweight or obesity is determined by more than how much you eat. It also includes the types and amount of food and drinks you consume each day, your level of physical activity (such as whether you sit at an office desk or are on your feet all day), and how much good-quality sleep you get each night.

All of these factors, as well as many others, can contribute to weight gain.

What raises the risk of overweight and obesity?

There are many risk factors for overweight and obesity. Some are individual factors like knowledge, skills, and behaviors. Others are in your environment, such as school, workplace, and neighborhood. Additionally, food industry practices and marketing as well as social and cultural norms and values can also impact your risk.

You may not be able to change all of your risk factors for overweight or obesity. But knowing your risk is important to help you take steps to reaching a healthy weight and lowering your risk for obesity-related health problems, such as heart disease.

Lack of physical activity

Lack of physical activity, combined with high amounts of TV, computer, video game, or other screen time has been associated with a high body mass index (BMI). Most adults need at least 150 minutes of aerobic activity a week. It is also recommended that adults do muscle-strengthening activities for major muscle groups on 2 or more days each week, as these activities give additional health benefits. Children should get 60 minutes of aerobic activity each day. See the recommendations for physical activity for different age groups.

Unhealthy eating behaviors

Some unhealthy eating behaviors can increase your risk for overweight and obesity.

  • Eating more calories than you use: The number of calories you need will vary based on your sex, age, and physical activity level. Find daily calorie needs or goals for adults as part the DASH Eating Plan. You can also find Tip Sheets for Parents for guidance on how many calories children need and ways to reduce screen time.
  • Eating too much saturated fat: According to the Dietary Guidelines for Americans, the amount of saturated fat in your daily diet should be no more than 10% of your total calories. For a 2,000-calorie diet, that’s about 200 calories or about 22 grams of saturated fat.
  • Eating foods high in added sugar: On a daily basis, try to limit the amount of added sugar in your diet to no more than 10% of your calories.

Not getting enough good-quality sleep

Research has shown a link between poor sleep — not getting enough sleep or not getting enough good-quality sleep — and a high BMI. Regularly getting less than 7 hours of sleep per night can affect the hormone that control hunger urges. In other words, not getting good-quality sleep can make us more likely to overeat or not recognize our body’s signals that we are full. Visit Sleep Deprivation and Deficiency for more information about the health effects of lack of sleep.

High amounts of stress

Long-term and even short-term stress can affect the brain and trigger your body to make hormones, such as cortisol, that control energy balances and hunger urges. These hormone changes can make you eat more and store more fat.

Health conditions

Some conditions, such as metabolic syndrome and polycystic ovary syndrome, cause people to gain weight. These medical conditions must be treated for a person’s weight to come close to or into normal range.


Some people are predisposed to being heavier. Researchers have found at least 15 gene that influence obesity. Studies show that genetics may play a more important role in people with obesity than in people who are overweight. For people with a genetic high risk for obesity, making healthy lifestyle changes can help lower that risk.


Some medicines cause weight gain by disrupting the chemical signals that tell your brain you are hungry. These include:

  • Antidepressants
  • Antipsychotics
  • Beta-blockers, which are used to treat high blood pressure
  • Birth control
  • Glucocorticoids, which are often used to treat autoimmune disease
  • Insulin, which is a hormone taken to control blood sugar levels in people with diabetes

Talk to your provider if you notice weight gain while you are using one of these medicines. Ask whether there are other forms of the same medicine or other medicines that can treat your medical condition but have less of an effect on your weight.

Your environment

Your environment can contribute to unhealthy eating and a lack of physical activity. Your environment includes all of the parts where you live and work — your home, buildings in which you work or shop, streets, and open spaces. The types of restaurants and the amount of green space you have can contribute to overweight and obesity.

Studies have shown that access to sidewalks and green spaces can help people be more physically active, and grocery stores and farmers markets can help people eat healthier. On the other hand, people living in neighborhoods with more fast food restaurants and inaccessible or no sidewalks or bath paths are more likely to be overweight or obese.

Research for your health

NHLBI-supported research addresses the increasing prevalence of obesity and translates findings into strategies to prevent or treat obesity and its health consequences.

Join an NHLBI clinical trial.

See if you or someone you love is eligible to join a clinical trial for overweight or obesity.


Last updated on