Causes and Risk Factors of Obesity

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Obesity is primarily caused by an imbalance between calories consumed and calories expended, though many 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.

A global health epidemic, obesity is classified as a disease in itself, but it is also a risk factor for many diseases, including diabetes, cardiovascular disease, musculoskeletal disorders, and certain cancers.

Like many chronic health conditions, obesity is largely preventable.


When it comes to obesity, the largest contributors are modifiable risk factors including diet, exercise, sleep, and stress. Making appropriate lifestyle changes is can help to reduce your likelihood of becoming obese.


It was long believed that the cause of obesity was eating more calories than your body burns. That contributes in many cases, most certainly. However, new research shows it may be more complicated than the simple calories in, calories out formula.

A 2019 study published in Cell Metabolism shows that all calories are not created equal. The type of food you eat has a greater impact on weight than calories alone.

In a four-week cross-over trial, subjects were fed calorie-matched diets of either highly processed foods or unprocessed foods for two weeks, then switched to the other diet. Participants gained an average of almost a pound on the processed food diet but lost almost a pound on the unprocessed diet. 

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

Other dietary factors linked to obesity are frequently dining out, not eating enough whole fruits and vegetables, and preparing meals at home less than seven times per week. Research has also pinpointed two dietary components that lead to weight gain and obesity: added sugar and saturated fat.

Added Sugar

The overconsumption of added sugar has been singled out by many experts as the most direct causal factor to 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 six teaspoons a day for women and nine teaspoons daily for men; the average American adult consumes an estimated 18 teaspoons of sugar a day.

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.

Major sources of added sugars are soft drinks, candy, baked goods, fruit drinks, milk products (such as ice cream and sweetened yogurt), and cereals.

Saturated Fat

Consumption of saturated fat has been linked to a higher risk of cardiovascular disease and, 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 published in the journal Biomedica shows 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

The increasingly sedentary lifestyle that more and more people around the world have adopted is directly linked to the global obesity epidemic.

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 remain sedentary for too long on a daily basis, which is associated with weight gain and obesity.

Research has shown that sitting still for as little as 30 minutes can have detrimental effects throughout the body.

Not Enough Sleep

Another cause of obesity linked to the modern lifestyle is sleep deprivation. 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.

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 2015 study, also in the journal Sleep, found that going to bed too late can result in weight gain, especially for teenagers and young adults.

In the study of 3,342 adolescents who were part of the National Longitudinal Study of Adolescent Health, a later bedtime was linked to an increased body mass index (BMI) over time. Consistently going to bed one hour later was associated with a two-point greater increase in BMI over a six-year period than subjects with an earlier bedtime. 


If you’ve ever given in to 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, spending time 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. For example, scientists have now discovered a gene— the FTO gene—that may confer a tendency toward binge eating and the development of obesity in adolescents.

The FTO gene also appears to be associated with effects on appetite, food intake, and body mass index (BMI). Based on study results, researchers now believe that there may be a relationship between FTO, binge eating, and obesity.

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

Interestingly, another study looking at the effects of FTO in over 3,000 Chinese children found that the effects of FTO on higher BMI also led to an associated risk of high blood pressure (hypertension), which is known to be caused by obesity.

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, medical issues, medications, and injuries can contribute to weight gain that may lead to obesity.

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

  • Hypothyroidism
  • Insulin resistance
  • Arthritis and other chronic pain conditions
  • Hormonal issues, including menopause
  • Polycystic ovary syndrome (PCOS)
  • Prader-Willi syndrome
  • Cushing syndrome

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
  • Oral contraceptives

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 2% to 5% of the population is diagnosed with binge eating disorder (BED). A psychological condition characterized by uncontrollable overeating, research shows 50% of patients seeking bariatric surgery for treatment of obesity also meet the diagnostic criteria for 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 doctor. These are causes of obesity that can be treated 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(s), keeping in mind that even small adjustments to your lifestyle and diet on a daily basis can add up over time. The bigger picture of your long-term health is worth the commitment.

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