A multitude of factors can contribute to obesity risk, including genetics, lifestyle choices, environment, and even social determinants.
Obesity is a chronic disease that occurs when a person has excess body fat, resulting in a high body mass index (BMI). According to the Centers for Disease Control and Prevention (CDC), a person with a BMI of 30 or higher is considered to have obesity.
A variety of factors — from genetics to diet and exercise to where you live — play a role in obesity risk. Understanding the potential underlying causes of obesity is essential to help individuals lose weight and improve their health.
Avoiding obesity is not as simple as burning the same amount of calories that you’re taking in. Whether someone develops obesity or not is often much more complex.
“The causes and risk factors for obesity are multifactorial: genetics, environment, lifestyle, and even socioeconomic status,” says Mir Ali, MD, a bariatric surgeon and the medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, California.
When we eat, our bodies turn food into energy that’s used for everyday functions and physical activity. The energy collected that isn’t used gets stored for the future as fat. If you regularly take in significantly more energy than the body can use each day, you may be at risk for developing obesity.
When it comes to satiety and nutrient density, not all foods are equal. Whole foods like veggies, fruits, whole grains, dairy, fish, nuts, and lean meats are high in nutrients. These foods are more likely to keep you feeling full longer than processed, packaged foods, such as bagged snacks, processed meats, and desserts.
“Processed foods are high in sugar and fat and low in fiber, which makes it easy to overeat,” says Lisa Young, PhD, RDN, a New York City–based nutrition consultant and author. She also points to larger portion sizes in general as a contributor to overeating.
Research suggests that eating highly processed foods is linked to weight gain because people are likely to consume more calories from carbohydrates and fat. According to a study, about two-thirds of the calories consumed by children and adolescents in the U.S. in 2018 came from highly processed foods. The percentage of calories coming from highly processed foods increased between 1999 to 2018 from about 61 percent to 67 percent for this group.
At the same time, the obesity rate among children ages 2 to 19 has steadily risen over the past two decades.
Lifestyle Choices
Lifestyle factors, including lack of regular exercise, excessive time sitting during the day, and insufficient quality sleep, can all influence obesity risk.
Routine physical activity allows the body to use the energy it takes in through food. If your activity levels are well matched with your calorie intake, your risk for obesity may be reduced. People who spend most of their day sitting, whether due to work or leisure, may not get the recommended amount of physical activity, leading to an increased risk of obesity.
The U.S. Department of Health and Human Services recommends the following activity guidelines:
Children ages 3 to 5 should be physically active throughout the day.
Children and adolescents ages 6 to 17 should get one hour or more of moderate or intense physical activity per day.
Adults should get at least 150 minutes of moderate to intense physical activity throughout the week.
Researchers have found a correlation between decreased physical activity levels and higher levels of childhood obesity.
Not getting enough quality sleep may also contribute to increased weight gain and obesity. Sleeping less than seven hours per night can affect hormones that regulate hunger, thus increasing appetite and making it less likely to recognize signs of being full.
This may explain why studies have found a link between short sleep duration and obesity risk.
Genetics
Genetics can play a role in whether someone develops obesity by affecting metabolism, appetite, cravings, and body-fat distribution. How much genetics influence obesity varies from person to person, but often genes are just one piece of the puzzle, with behavior and environment also being contributing factors.
When obesity is caused by a specific disorder, such as Bardet-Biedl syndrome or Prader-Willi syndrome, genes do play a direct role, according to the CDC. However, these types of syndromes are rare. (See more on medical conditions that can increase obesity risk below.)
Environment
Your environment — from where you live to where you work and play to whom you interact with on a regular basis — can impact your health.
For example, if you work in an office and live in a place where you have to drive rather than walk to get around, you may be less likely to get regular physical activity. Some research suggests that high neighborhood walkability (how easy it is to get around on foot in an area) could be associated with lower rates of obesity.
Environmental substances like air pollution and other chemical pollutants found in items we use in our homes can also play a role. A large study found that exposure to air pollution in early years was linked to an increased risk for children developing obesity.
Another study examined the potential effects of perfluoroalkyl substances (PFASs), which are chemicals made by humans and used in packaging and household items. The researchers found that women with a higher concentration of PFASs in their blood levels at baseline regained more weight after losing weight by a calorie-restricted diet during the study compared with women with a lower concentration of PFASs. The study demonstrated the possibility for these chemicals to have an impact on metabolism and weight regulation; however, it did have some limitations because other factors for possible weight gain weren’t measured.
Social Determinants
Social determinants of health are circumstances beyond individuals’ control that impact our communities and lives, per the U.S. Department of Health and Human Services. Socioeconomic status is a social determinant that can contribute to obesity. Low-income communities often lack access to healthy food sources, leading to higher consumption of highly processed foods, as well as safe places to exercise outdoors.
The CDC also points to a link between education and obesity, with those holding college degrees less likely to have obesity.
Stress
Stress can contribute to obesity by prompting changes in our eating patterns and hormones. Although research has linked stress with eating foods for comfort, that doesn’t mean experiencing short periods of stress will lead to weight gain.
But long-term, or chronic, stress can create risk factors for obesity. One factor at play is cortisol, a stress hormone that can increase appetite and signal your body to store more fat.
Other Medical Conditions
In addition to stress, childhood trauma and mental health diagnoses like anxiety and depression are linked to an increased risk of obesity.
Other medical conditions are associated with weight gain, which could potentially lead to obesity. These conditions include:
Some medications can cause weight gain as a side effect by creating an increased appetite when hormones regulating hunger are disrupted. Over time, these could be a contributor to obesity.
The National Heart, Lung, and Blood Institute lists the following medications as causes of weight gain.
If you feel like your medication is causing weight gain, talk to a healthcare professional. They may be able to recommend something different that doesn’t impact your weight.
A variety of factors, from genetics to lifestyle choices to your environment, play a role in obesity risk.
While certain factors like family history cannot be controlled, making changes to diet, physical activity levels, and stress can help reduce your risk of obesity.
Some medical conditions, along with certain medications like antidepressants, antipsychotics, and birth control, can sometimes lead to weight gain. Talk to your doctor if you have concerns about any of the medication you’re taking.
