What Causes Obesity?

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Medically reviewed by Jane Kim, MD

Obesity is a common condition that happens when your body develops an excessive amount of fat tissue. The World Health Organization (WHO) estimates that 1 in 8 adults have obesity worldwide. Obesity develops over time when the body takes in more energy (calories) than it uses. Consuming more calories than your body burns leads to an energy imbalance.

When you eat, your body uses the nutrients from your food for immediate energy. Any extra fuel (such as sugar and fat) is stored for later use. Sugar becomes stored as glycogen in the liver and muscles, while fats are stored as triglycerides in fatty tissue. Excess sugar and fat in your body can lead to obesity. In turn, obesity can be a risk factor for serious health problems like type 2 diabetes, heart disease, and certain cancers.

Several factors can increase your risk of developing obesity. Knowing these underlying causes and risk factors can help you prevent obesity and improve overall health outcomes.

How Is BMI Related to Obesity?

Healthcare providers usually diagnose obesity using a person’s body mass index (BMI). A BMI over 30 is usually considered obese. Healthcare providers calculate BMI based on your weight and height.

While BMI is still widely used, it does not capture all of your medical information and does not give a full picture of your overall health. It should not be the only metric used to assess your well-being.

Eating Habits

Your diet or eating plan significantly affects your weight and risk of obesity. Consuming more calories than your body burns leads to fat accumulation. Over time, this can raise the risk of obesity.

Consuming high amounts of saturated fat and sugar increases the risk of obesity. Ultra-processed like store-bought cookies, chips, candy, and soda can especially spike your blood sugar and cause your body to store excess sugar and fat. Researchers believe that a diet rich in ultra-processed foods is not only a strong risk factor for obesity, but can also raise your risk of type 2 diabetes, heart disease, and depression.

Lack of Physical Activity

Physical activity burns calories and uses up stored energy in your body. A lack of physical activity increases the risk of obesity because the body is more likely to take in more energy than it uses. Researchers have found that people are more likely to have a high BMI when they are not physically active and also report high amounts of screen time from television, computers, video games, and phones.

Healthcare providers recommend adults get 150 minutes of aerobic activity each week. This may include brisk walking, swimming, or any physical activity that gets your heart pumping. Adults can also benefit from muscle-strengthening workouts twice a week. For young children, healthcare providers recommend 60 minutes of aerobic activity every day.

Sleep Problems

Experts have found a strong link between lack of sleep and weight. That’s because sleep affects your hormones and hunger levels. If you sleep poorly on most nights of the week, you may experience more hunger cues or cravings during the day. This can lead to eating more calories than the body can use.

Not getting enough sleep also includes people who have trouble falling asleep and those who wake frequently throughout the night. Underlying health conditions like insomnia or delayed sleep phase syndrome can also affect your sleep quality greatly.

Stress

Long-term stress may raise the risk of obesity over time. Stress causes your body to release hormones like cortisol. These hormones affect your energy and hunger levels. People who are under chronic stress may crave high-density foods that are high in sugar and fat, which can often lead to an energy imbalance and weight gain.

Underlying Health Conditions

Some chronic health conditions can increase your risk of obesity. For example, you may experience more weight gain, even if you’re not trying to gain weight. Conditions that can contribute to this include:

• Metabolic syndrome: A group of medical conditions (e.g., high blood sugar, high blood pressure) that increase your risk for diseases such as heart disease, stroke, and type 2 diabetes

If you have a diagnosis for any of these conditions, work with your healthcare provider to learn how to keep your body at a weight that is right for you and lower your risk of obesity.

Genetics

Your genetics play a role in your risk of obesity. In fact, researchers know of 15 genes that influence obesity. Changes or mutations in these genes may affect hunger cues and how much food you consume.

Medications 

Certain medications may contribute to weight gain because they affect hunger cues. Medications known to cause weight gain include:

• Antidepressants and antipsychotics: Treat mental health conditions like depression or anxiety
• Beta-blockers: Treat heart disease and high blood pressure
• Birth control pills: Used to prevent pregnancy and treat conditions like anemia, painful periods, and premenstrual syndrome (PMS)
• Glucocorticoids: Treat inflammation
• Insulin: Treats high blood sugar and diabetes

Environmental Factors

While your lifestyle habits and genetics can influence your weight, environmental factors can contribute to your obesity risk.

For example, if you don’t have proper access to nutritious foods via grocery stores or farmers’ markets and free areas to get physically active such as safe streets and green spaces, you may be at an increased risk of obesity. Unfortunately, these environmental inequalities often affect people who live in low-income neighborhoods.

Eating Healthy on a Budget

For more information on how you can access nutritious foods on a budget, check out Health’s article here.

Modifiable vs. Unmodifiable Risk Factors

There are several known risk factors for obesity—and some risk factors can be changed. These are known as modifiable risk factors, which may include:

• Eating high amounts of sugar and saturated fats
• Not engaging in enough physical activity
• Getting poor sleep
• Experiencing chronic stress

Some risk factors are more difficult to address. Risk factors that do not change or may be beyond your control include:

• Family history of obesity
• Chronic health conditions 
• Certain medications
• Socioeconomic status
• Living in an area without access to healthy food or places to exercise 

A Quick Review

Obesity is a common chronic health condition that occurs when your body has an excessive amount of fat tissue. This happens when the body takes in more energy (calories) than it uses, causing an energy imbalance. As a result of this imbalance, obesity can occur.

Common causes of obesity may include eating a diet high in sugar, not getting enough physical activity, and experiencing stress. Addressing these modifiable risk factors can lower your risk of obesity and improve health outcomes.

Read the original article on Health.com.