Genetic causes of obesity include monogenic, polygenic, and syndromic obesity. Mutations in one or more genes may cause early-onset obesity or affect appetite regulation. Nearly 42% of adults in the United States live with obesity. Genetics, lifestyle, and environmental factors all influence this condition.

What are the genetic causes of obesity?

Family and twin studies suggest that genetics play a role in about 40–60% of obesity cases. Genes can increase your risk in three major ways: monogenic, polygenic, or syndromic obesity.

Monogenic obesity
This occurs when a single gene mutation leads to obesity. Many types involve the LEPR gene, which causes leptin or leptin receptor deficiencies. Leptin is a hormone that regulates appetite. Monogenic obesity is often diagnosed in childhood and is sometimes referred to as early-onset obesity.

Polygenic obesity
Polygenic obesity develops when many different genes or polymorphisms (small variations in genes) influence body weight. Researchers have identified more than 500 obesity-related genes, including the FTO gene. A combination of these genetic variations can affect eating behaviors and activity levels, making it easier to gain weight when combined with high-calorie diets and sedentary lifestyles.

Syndromic obesity
Syndromic obesity usually begins early in life, often before age five, and tends to be severe. It is frequently associated with developmental delays or physical abnormalities. Conditions such as Bardet-Biedl syndrome (BBS) and Alstrom syndrome are examples of syndromic obesity.

How environmental factors lead to obesity

Obesity is not purely genetic. An environment that promotes weight gain is called an obesogenic environment, which encourages poor eating habits and limited physical activity.

Examples of obesogenic factors include:

  • Limited exposure to natural light in certain regions

  • City layouts that promote car use instead of walking

  • Food deserts with limited access to healthy groceries

  • Increased screen time through TV, computers, or gaming

  • Poverty and limited resources

Environment can also influence genetic expression through epigenetics. For example, childhood eating patterns can modify genes and increase obesity risk later in life. Epigenetic research may help predict obesity risk based on environmental exposure.

What are the risk factors?

Obesity risk is influenced by multiple factors, often linked together:

Health conditions: Disorders such as PCOS, hypothyroidism, diabetes, and depression can cause hormonal imbalances that lead to weight gain.
High-calorie diet: Overeating, especially without physical activity, contributes to obesity. Diets high in refined carbs can also promote insulin resistance and type 2 diabetes.
Maternal health: Smoking or obesity during pregnancy increases a child’s risk of developing obesity later.
Physical inactivity: Sedentary lifestyles raise the likelihood of weight gain.

Treatment options for obesity

Even with genetic predisposition, obesity can often be prevented or managed. Treatment may include:

  • Eating a balanced diet designed with a registered dietitian

  • Engaging in at least 150 minutes of aerobic exercise weekly

  • Sleeping at least seven hours daily

  • Managing stress with practices such as yoga, meditation, or journaling

In some cases, healthcare providers may prescribe medications or recommend surgery if lifestyle changes alone are not effective. Professional support can also help address related conditions such as diabetes, sleep apnea, or heart disease, as well as mental health issues like depression or anxiety.

When to seek care

If you are concerned about your weight, talk with a healthcare provider. They may refer you to a dietitian or mental health specialist to develop a personalized weight management plan. Even if you do not have obesity but have a family history or genetic predisposition, a healthcare provider can help you take preventive steps.

A quick review

Genetics play a significant role in obesity, with family history and gene mutations increasing risk. However, obesity is largely preventable and reversible. By working with a healthcare provider, you can develop a lifestyle and treatment plan tailored to your needs to reduce risks and improve long-term health.