Causes and Risk Factors of Obesity

Obesity is primarily caused by an imbalance between calories consumed and calories expended. However, many risk factors contribute to the disease. While lifestyle choices like poor eating habits and not enough exercise are chief causes of excess weight, people can be predisposed to obesity due to genetics or certain medical conditions.

Overweight woman buttoning up her jeans
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The largest contributors to obesity are modifiable risk factors such as diet, exercise, sleep, and stress. Making appropriate lifestyle changes can help reduce your likelihood of becoming obese.


Obesity can develop over time when you take in more calories than you use. This calorie imbalance causes your body to store fat. The number of calories can affect your weight gain, but research shows that other factors can determine how your body uses those calories—and, therefore, the amount of weight you gain.

Processed Foods

Not all calories are created equal. Some foods and eating patterns can determine how many calories you’re likely to consume.

In a 2019 study, subjects were fed calorie-matched diets of either highly-processed or unprocessed foods for two weeks, then switched to the other diet. The subjects were instructed to eat as much or as little as they wanted throughout the study.

The results found that the participants on the processed-food diet consumed more calories and gained an average of about 1 pound compared to those who ate only unprocessed foods, who ate fewer calories and lost almost 1 pound on average. In addition, appetite-suppressing hormones increased more with the unprocessed food diet than the processed food diet.

You can help reduce the number of processed foods you eat by:

  • Limiting fast food
  • Preparing more meals at home
  • Choosing whole grains over refined grains, which are more processed
  • Increasing your consumption of whole fruits, vegetables, nuts, and healthy sources of protein, such as poultry, fish, and beans

Limiting processed foods may be an effective strategy for obesity prevention and treatment.

Added Sugar

The overconsumption of added sugar is a risk factor in the long-term development of obesity. “Added sugar” refers to all sugars that are added to food, rather than those that occur naturally (such as in fruit).

The American Heart Association (AHA) recommends limiting added sugar to less than 6 teaspoons a day for women and 9 teaspoons daily for men.

Part of the problem is that added sugar goes by many names. So, unless you are reading the ingredients label carefully, you may not realize how many different kinds of sugar have been added to what you’re eating or drinking.

Other names for added sugar include:

  • Maltose
  • Sucrose
  • Molasses
  • High fructose corn syrup
  • Cane sugar
  • Syrup
  • Corn sweetener

Saturated Fat

Consumption of saturated fat has been linked to a higher risk of cardiovascular disease. Given that foods that are high in saturated fat are often calorie-dense, this likely plays a role in the development of obesity as well.

A 2018 study found that eating a meal that is high in saturated fat impacts insulin sensitivity, leading to higher post-meal blood sugars and inflammation that contribute to obesity.

Too Little Exercise

A sedentary lifestyle can lead to a greater risk of obesity. From driving to work each day to sitting at a desk for hours on end—and then, for many, going home and sitting in front of the television—many people remain sedentary for too long on a daily basis, which is associated with weight gain and obesity.

Data from the Centers for Disease Control and Prevention (CDC) shows that obesity rates tend to be higher in areas where adults report no physical activity in their leisure time.

Not Enough Sleep

Another cause of obesity linked to the modern lifestyle is sleep deprivation. Experts recommend seven to nine hours of uninterrupted sleep per night to reap the health benefits of rest, including those related to preventing obesity.

A 2012 study in the journal Sleep found getting too little sleep can result in metabolic changes that can lead to weight gain.

In the study, subjects who slept four hours a night had higher levels of ghrelin, a hormone that increases appetite. The study authors suggest that too little sleep contributes to weight gain by boosting hunger signals leading to overeating.

Research also shows that children and teenagers have a higher rate of obesity if they don’t get enough sleep. A 2018 study found that adolescents who consistently didn’t get enough sleep had a higher body mass index (BMI) than those who did.

BMI is a dated, flawed measure. It does not take into account factors such as body composition, ethnicity, sex, race, and age. 
Even though it is a biased measure, BMI is still widely used in the medical community because it’s an inexpensive and quick way to analyze a person’s potential health status and outcomes.

The American Academy of Sleep Medicine recommends that children 6 to 12 years should sleep nine to 12 hours per night; teenagers should sleep eight to 10 hours per night.


If you’ve ever given into emotional eating or the craving for “comfort food,” you know firsthand how stress can affect the way you eat.

Chronic stress also causes the body to activate biological pathways involving stress-related factors and stress hormones, such as cortisol, which causes the body to hold on to extra weight more easily.

Some of the healthiest ways to beat stress also turn out to be ways to fight obesity in general. These include taking regular walks, developing an exercise routine, bonding with your pet, and taking the time to prepare and enjoy a home-cooked meal.


Biological links to obesity, including particular gene mutations, are continually being researched and uncovered. Studies have found variants in genes that may contribute to obesity, including those that may influence behaviors or metabolism. Obesity is likely to be caused by interactions among multiple genes as well as environmental factors.

Scientists have discovered genes that may confer a tendency toward the development of obesity in adolescents. In particular, the FTO gene appears to be associated with effects on appetite, food intake, and BMI. Based on study results, researchers now believe that there may be a relationship between FTO, binge eating, and obesity.

In another study of nearly 1,000 patients, scientists found four genetic markers (one of which involved FTO) that were associated with higher BMI at the age of 13.

Uncovering such links may be important to new treatments for obesity and related concerns.

Medical Conditions

While obesity is typically related to diet and exercise levels, it could also be affected by medical issues, medications, and injuries.

Medical conditions can lead to weight gain by slowing your metabolism, increasing your appetite, or reducing your mobility. These include:

Many medications can contribute to weight gain if you don't compensate through diet or activity. Medications associated with weight gain include:

  • Anticonvulsants, such as carbamazepine and valproate
  • Antidepressants
  • Antihistamines
  • Corticosteroids, such as prednisone
  • Diabetes medications, including insulin, sulfonylureas, and thiazolidinediones
  • High blood pressure medications, such as beta-blockers

Psychological factors also contribute to obesity. While many people turn to food in response to emotions such as stress, boredom, sadness, or anger, an estimated 3% of the population is diagnosed with binge eating disorder (BED).

If you believe you may be gaining weight due to a medical condition or have noticed weight gain after starting a medication, be sure to discuss your concern with your healthcare provider. These are causes of obesity that can be addressed and usually reversed.

A Word From Verywell

There are many known causes of obesity. If you recognize that any of the above apply to you or a loved one, resolve to take action to address the cause, keeping in mind that even small adjustments to your lifestyle and diet on a daily basis can add up over time. The prospect of better long-term health is worth the commitment.

Frequently Asked Questions

  • What is the obesity rate in the United States?

    According to the Centers for Disease Control and Prevention, the obesity prevalence was 42.4% from 2017 to 2018. That number is a significant increase compared to the years 1999 to 2000, when the rate was 30.5%.

  • What are the risk factors for obesity in childhood?

    The risk factors for obesity in children are similar to those for adults, such as eating high-calorie processed foods, lack of exercise, and a family history of obesity. Families, communities, and schools can help decrease the risks by providing healthy food choices and opportunities for physical activity.

  • What are the health risks of obesity?
20 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Heart, Lung, and Blood Institute. Overweight and obesity

  2. Harvard School of Public Health. Obesity prevention source: food and diet. 

  3. Hall K, Ayuketah A, Brychta R et al. Ultra-processed diets cause excess calorie intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake. Cell Metab. 2019;30(1):67-77.e3. doi:10.1016/j.cmet.2019.05.008

  4. Johns Hopkins Medicine. Obesity, sugar and heart health.

  5. American Heart Association. Added sugars.

  6. Alayón AN, Rivadeneira AP, Herrera C, Guzmán H, Arellano D, Echeverri I. Metabolic and inflammatory postprandial effect of a highly saturated fat meal and its relationship to abdominal obesityBiomédica. 2018;38:93-100. doi:10.7705/biomedica.v38i0.3911

  7. Barnes AS. Obesity and sedentary lifestyles: risk for cardiovascular disease in women. Tex Heart Inst J; 39(2):224-227.

  8. St-Onge M, O'Keeffe M, Roberts A, RoyChoudhury A, Laferrère B. Short sleep duration, glucose dysregulation and hormonal regulation of appetite in men and women. Sleep. 2012;35(11):1503-1510. doi:10.5665/sleep.2198

  9. Jansen E, Dunietz G, Chervin R, et al. Adiposity in adolescents: the interplay of sleep duration and sleep variability. J Pediatr. 2018;203:309-316. doi:10.1016/j.jpeds.2018.07.087

  10. American Academy of Sleep Medicine. Recharge with sleep: pediatric sleep recommendations promoting optimal health.

  11. Jackson S, Kirschbaum C, Steptoe A. Hair cortisol and adiposity in a population-based sample of 2,527 men and women aged 54 to 87 years. Obesity. 2017;25(3):539-544. doi:10.1002/oby.21733

  12. Centers for Disease Control and Prevention. Behavior, environment, and genetic factors all have a role in causing people to be overweight and obese.

  13. Micali N, Field AE, Treasure JL, Evans DM. Are obesity risk genes associated with binge eating in adolescence?  Obesity. 2015;23(8):1729-1736. doi:10.1002/oby.21147

  14. Lombard Z, Crowther N, van der Merwe L, Pitamber P, Norris S, Ramsay M. Appetite regulation genes are associated with body mass index in black South African adolescents: a genetic association study. BMJ Open. 2012;2(3):e000873. doi:10.1136/bmjopen-2012-000873

  15. Gao M, Liu D. Gene therapy for obesity: progress and prospectsDiscov Med. 2014;17(96):319-328.

  16. Weaver JU. Classical endocrine diseases causing obesityFront Horm Res. 2008;36:212-228. doi:10.1159/000115367

  17. Kulkarni SK, Kaur G. Pharmacodynamics of drug-induced weight gainDrugs Today; 37(8):559-571.

  18. Centers for Disease Control and Prevention. Adult obesity facts.

  19. Centers for Disease Control and Prevention. Childhood obesity causes and consequences.

  20. Centers for Disease Control and Prevention. Adult obesity causes & consequences.

Additional Reading

By Yasmine S. Ali, MD, MSCI
Yasmine Ali, MD, is board-certified in cardiology. She is an assistant clinical professor of medicine at Vanderbilt University School of Medicine and an award-winning physician writer.