Causes and Risk Factors of Obesity

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Obesity is caused by an energy imbalance between calories consumed and calories expended. Many factors contribute to obesity, including a poor diet, lack of exercise, certain medications, medical conditions, socioeconomic factors, and genetics. 

Globally, more than 650 million people are obese, according to the World Health Organization 2016 statistics. 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.

Common Causes

It was long believed the primary cause of obesity was eating more calories than your body burns, however, new research shows it may be more complicated than the 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 1 pound on the processed food diet but lost almost 1 pound on the unprocessed diet. 

The study authors note that limiting processed foods may be an effective strategy for obesity prevention and treatment. 


Diet impacts weight in other ways as well. Eating too much sugar and saturated fat, as well as frequently dining out are also factors.

Other dietary factors that have been associated with a higher risk of obesity include not getting enough whole fruits and vegetables in the daily diet and preparing meals at home less than seven times per week.

Research has pinpointed two dietary components that contribute to weight gain and obesity: sugar and saturated fat.


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.

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

Food manufacturers have found many different methods and sources by which to add sugar to foods ranging from ketchup to cereal to soft drinks, so look for the following on labels: any ingredient ending in “-ose” (such as maltose, dextrose, sucrose, fructose, lactose, high fructose corn syrup), molasses, cane sugar, corn sweetener, evaporated cane juice, raw sugar, syrup, and fruit juice concentrates.

Major sources of added sugars in our diets are soft drinks, candy, cakes, cookies, pies, fruit drinks, dairy desserts and 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. 

Medical Factors

While obesity is typically related to diet, there are some medical disorders that can contribute to weight gain that leads to obesity. Some such conditions include hypothyroidism, polycystic ovary syndrome, and Cushing syndrome, to name a few.

In addition, some medications, such as certain antidepressants and steroids, are linked to weight gain.

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, but medical intervention is required to do so.


Biological links to obesity, including particular gene mutations, are continually being researched and uncovered. For example, scientists have now discovered a gene, known as the FTO gene, that may confer a tendency toward binge eating and 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 the FTO gene) that were associated with higher BMI at the age of 13.

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. It is even possible that gene therapy could one day be used to treat obesity.

Lifestyle Risk Factors

Over time, many daily lifestyle habits can contribute to the development of 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 of us remain sedentary for too long on a daily basis, which is associated with weight gain and obesity.

A sedentary lifestyle is also associated with an increased risk of cancer, and cardiovascular disease. 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. Experts recommend seven to nine hours of uninterrupted sleep per night to reap the health benefits of good sleep, 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 4 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.

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 2-point greater increase in BMI over a six-year period than subjects with an earlier bedtime. 


Chronic stress is associated with obesity for a variety of reasons. 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 causes the body to activate biological pathways involving stress-related factors and stress hormones, such as cortisol, which also cause 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 become less sedentary and 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.

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 the long term. The bigger picture of your long-term health is worth a few small changes to your daily routine.

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Article Sources

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