Obesity is a health condition with several known risk factors, including certain medications, unhealthy eating habits, and other health conditions.

Doctors may diagnose someone with obesity if they have a body mass index (BMI) of 30 or more.

The Centers for Disease Control and Prevention (CDC) report that obesity affected about 42% of people in the United States in 2017. This is an increase of more than 10 percentage points from 31% in 1999.

Obesity can lead to several other health conditions, including heart disease, type 2 diabetes, stroke, and certain cancers. Living with obesity may also increase a person’s personal medical costs.

Several factors can increase a person’s risk of having obesity. A person may take steps to address some of them and reduce their chances of developing obesity.

This article reviews some of the risk factors for obesity as well as when to speak with a doctor.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Stress affects the brain. It also triggers the release of hormones, such as cortisol, which helps to control energy use and hunger.

These hormonal changes may cause a person to eat more and their body to store more fat.

Studies have shown that sleep deprivation and obesity share a bidirectional link. Lack of sleep may lead to fatigue and lower capacity to exercise, along with changing chemicals in the body that can promote weight gain. Meanwhile, obesity may increase a person’s risk of experiencing sleep disorders.

In other words, experiencing one condition may increase the risk or worsen the effects of the other condition.

Living with certain health conditions may increase a person’s risk of having obesity.

Some health conditions that can lead to obesity include:

Learn more about metabolic disorders here.

The environment a person lives in can play a role in increasing their likelihood of developing obesity.

Different studies have looked at the effect that a person’s ethnicity, gender, and socioeconomic status have on obesity risk.

According to a 2019 article, multiple environmental factors can interact with each other and increase obesity risk. They include:

  • food availability — some people may live in “food deserts,” where they lack access to fresh, healthy food options or have higher availability of fast food or processed foods
  • food perceptions — some people believe that calorie-dense and nutrient-deficient foods are more affordable
  • lack of access to sidewalks, green spaces, parks, or other areas that may encourage more physical activity
  • higher crime rates
  • changes in work environments, so people are less physically active
  • social inequalities that can lead to food insecurity and disruptions in dietary patterns

These factors can play a complex role, with each interacting with the others to create an environment that may make obesity more likely. They may also disproportionately affect certain groups, including:

  • females, particularly if they are non-Hispanic Black, non-Hispanic Asian, or Hispanic
  • people living in rural neighborhoods
  • people with low income
  • people with less education

Learn more about health equity here.

Unhealthy eating habits can lead to weight gain and obesity. Poor eating habits include:

  • eating more calories than necessary
  • consuming foods containing high amounts of added (less than 10% of total daily calories should come from added sugar)
  • eating foods high in saturated fat (less than 10% of daily calories should come from saturated fat)

A person’s diet should include foods such as:

Physical activity can play an important role in keeping a person healthy and preventing obesity. A rise in sedentary lifestyles due to urbanization, access to transportation, changing employment, and lack of physical movement may have contributed to the global increase in obesity.

A person can make small changes to start increasing their activity levels, such as:

  • taking the stairs instead of the elevator
  • going for short walks
  • playing a sport recreationally

Different medications may contribute to weight gain. Some common examples of medications that can cause weight gain include:

If a person gains weight while taking any medications, they may decide to speak with a doctor about different medication options that do not cause weight gain. Alternatively, a healthcare professional may be able to help a person manage their weight safely while they use medications.

A person’s genes can also play a role in obesity and weight gain.

According to a 2021 study, at least 15 different gene defects account for monogenic obesity cases, which refers to obesity that results from a deficiency or mutation of one particular gene.

The authors also noted that thousands of variants in genetics make it difficult to treat and prevent genetically based obesity.

A person may want to speak with a doctor if they start to gain weight for unknown reasons. A doctor can help identify if it is due to an underlying health condition or medication.

In some cases, healthcare professionals recommend dietary modifications, exercise plans, or other methods to help manage and maintain weight.

A person with obesity may want to see a doctor regularly for health checks. This helps prevent complications resulting from obesity.

There are several potential risk factors that have links with obesity, including underlying health conditions, taking certain medications, and lack of sleep.

A person can take steps to help prevent weight gain and obesity by increasing their physical activity and modifying their diet.

People who have trouble maintaining a healthy weight may decide to speak with a doctor, who can provide additional support and advice about safely managing weight.