17 Main Causes of Obesity

by Rakib Sarwar, RPh
Published on July 24, 2019

According to the World Health Organization, 39% of the world’s population is overweight (1). Over the past thirty years, the number of obese people doubled and it tripled over the past 40 years (1)! Today, obesity represents a big challenge because more people die from the consequences of obesity than from malnutrition.

What are the causes of obesity? How can understanding each cause lead to a healthier lifestyle and protecting oneself from becoming overweight and/or obese? Stay with us and find out the answers to these and many more questions on obesity.

What is obesity

Let’s first define obesity. Obesity is a state of excessive accumulation of fatty tissue in our body with consequent adverse effects on our general health. In addition, obesity was recently defined as a chronic and progressive disease process (2).

Determining obesity

Several simple and practical methods are used to determine the state of obesity:

  1. Determination of the body mass index (BMI),
  2. Measurement of the waist circumference, and
  3. Measuring the thickness of the skin fold.

Determining obesity through the BMI index calculation

Body mass index (BMI) is calculated by simply dividing the body weight expressed in kilograms with the height expressed in meters. Based on the obtained results, the respondent is classified into a certain category.

There are several BMI classifications, categories and subcategories accepted by science. The following one is the most general, widely accepted classification.

People with BMI between 20 and 25 have normal body weight. Those with BMI from 25 to 30 have excessive body weight (are overweight), while those with BMI from 30 to 35 are considered obese. The last, most severe category, denotes the BMI over 35 and is marked as stage II obesity (3).

Determining obesity through waist circumference measurement

Measuring the waist circumference determines the distribution of fatty tissue in the human body. On this basis, we determine the type of obesity (4). In fact, male and female types of obesity differ in practice.

In the case of male obesity, fatty tissue is formed around the waist (the so-called “apple” form), while the female type of obesity is marked with fatty tissue accumulated under the waist, lower abdominal area, buttocks, hips, and thighs (the so-called “pear” shape). If the waist circumference is larger than 102 cm in men and larger than 88 cm in women, it indicates obesity.

Determining obesity with a skinfold caliper

By measuring the thickness of the skin fold (5) we determine the percentage of body fat. With the use of special equipment, the so-called skinfold caliper, we can measure the thickness of the skin folds in several different regions of our body. The percentage of body fat is calculated and the results determine obesity or normal condition. The percentage of body fat greater than 25% in men and greater than 30% in women shows obesity.

Determining obesity in children and adolescents

In children and adolescents, the degree of obesity is determined by analyzing the percentile BMI curves by age and sex. Excessive body weight is diagnosed in children with BMI between 85 and 95 percentiles and is obesity in cases of BMI greater than 95 percentiles for the specific age group.

Main causes of obesity

Generally, we can say that the main cause of obesity is the lack of balance between the intake of calories intake and consumption of calories. However, there are many different reasons and causes of obesity in the background. Nutrition experts, medical specialists, lifestyle and health experts, as well as dietitians, have made the full list of the causes of excessive weight gain and obesity (6). Here it is:

  • Increased intake of calories,
  • Lack of physical activity,
  • Genetic predispositions,
  • Hormonal disbalance,
  • Psychosocial causes of obesity,
  • Cultural influences,
  • Various diseases and disorders,
  • Fast food and junk food consumption,
  • Skipping meals (especially breakfast),
  • Inadequate consumption of fruits and vegetables in the daily diet,
  • Insufficient fluid intake (water) in the body,
  • Intake of alcohol, carbonated and sweetened drinks,
  • Great intake of salt,
  • Insufficient sleep,
  • Certain medications (antidepressants),
  • Stress,
  • Excess weight gained during pregnancy.

Let’s learn more information about the top causes of obesity, in detail.

#1 – Excessive intake of food

The number 1 main cause of obesity is the excessive intake of food. If it is combined with insufficient physical activity, which we will talk about in detail as the #2 cause of obesity, it results in excess energy being consumed by food and not spent by work and physical activity (7). That excess energy is stored in your body in the form of fatty tissues.

The biggest problem is the lack of knowledge of proper food consumption. Also, many people don’t know how to read and analyze the labels on the products that provide information on the nutritive values of food.

The number of calories per serving is the first thing to look at. You should know how many grams of the product represents the recommended portion. As a result, instead of eating a whole box of biscuits and intaking a handful of calories, you will eat only the recommended portion of the product clearly specified on the label. This is very important if you want to control your weight through the calorie intake rules.

If you know the recommended daily caloric intake for your age group, sex, health condition, and BMI, you can easily increase or decrease the portion size, thereby contributing to increase or decrease your body weight.

For example, if your recommended daily calorie intake is 2000 Kcal and you have eaten a bag of chips containing 500 Kcal per serving, this is already a quarter of the calories you need to take in one day.

Now, let’s talk about fats. The labels usually contain information on the total fats. There are saturated and unsaturated fats. Saturated fats cause an increase in cholesterol level in your blood. The daily intake of saturated fat must not exceed 10%, which is expressed in percentages and grams on the label.

When it comes to proteins, you must know that they are extremely important. Why? They are responsible for building muscles. Proteins are especially important for people who are engaged in intense physical activities. Regenerating and restoring muscle fibers after a hard workout is mostly related to the protein intake after your training. Daily protein intake should be at least 1gr per kilogram of your body weight.

#2 – Sedentary lifestyle

One of the factors for developing obesity and significantly increased number of obese people in the world is reduced body activity. It is related to the predominantly sedentary lifestyle (6).

Changes in everyday habits that have occurred in the last few decades have influenced the increase in the number of obese people worldwide. This is especially visible in the developing countries, where people work a lot in their offices, but don’t have enough time for relaxation, exercising, and healthy lifestyle.

Reduced physical activity, in combination with excessive intake of high-calorie food, refined, and fatty foods, over-consumption of alcohol and lots of stress, increases the risk of developing obesity. It is also associated with the development of various diseases that further reinforce obesity development. We will talk about those diseases in the following sections.

#3 – Genetic factors

Genetic factors affect fat metabolism and regulate hormones that regulate our appetite. It is important to point out that the experts state that genetic factors play a very significant role in forming obesity, up to 70%!

A large number of genetic variations affect the occurrence of obesity (6). Hereditary factors may include fat distribution patterns, metabolism rate, excessive eating urge, personal preferences regarding favorite food, etc.

Genetic predispositions are directly responsible for some cases of extremely severe obesity. Although genetic abnormalities affect easier or more difficult weight loss of the individual, the dominance of obesity over the last 20 years is dramatically increasing, while genes cannot change so quickly.

Obesity is most common in people with normal physiology living in industrialized countries with abundant food. Therefore, it is not a consequence of the metabolic activity – response mechanism of our body to lack of food in the form of storing energy as fat.

According to one theory, type 2 diabetes mellitus and obesity, commonly associated with this disorder, originate from genetic actions that were once necessary for survival. Some experts claim that there is a so-called “curable” gene that regulates the flow of hormones to adapt to seasonal changes. In some nomadic nations, hormones are released during the season in which food quantities are always very limited, resulting in insulin resistance and effective fat storage. This process now turned to seasons when there is enough food.

As foods with high carbohydrate content and fat have become available thanks to industrialization, and are available throughout the year, this gene no longer serves its purpose. As a matter of fact, it became detrimental because fats originally stored for starvation periods are not consumed at all. This theory could explain the high incidence of type 2 diabetes and obesity among native Americans with nomadic history and Western nutrition habits.

Traditional foods with low-fat content and high content of fiber that the nomadic people used to consume were likely to protect this genetically sensitive population from frequent cases of obesity and type 2 diabetes, which is no longer the case today.

#4 – Hormonal disbalance

Contemporary medicine established the link between hormonal disbalance and obesity (7). Modern science knows that the hormone of hunger and hormone of satiety control our behavior regarding food consumption.

When we are hungry, the level of the hunger hormone is high and it stimulates the brain cells that give us the impulse to eat. After the meal, the level of this hormone drastically decreases.

The opposite effect can be observed through the analysis of a hormone called leptin. It is a hormone released by the fatty tissue. It sends signals to our brain cells that notify us when we are full, i.e. they are responsible for the feeling of satiety. High levels of leptin cause a lack of appetite. Also, abnormally high levels of the hunger hormone cause a constant feeling of hunger.
Therefore, the imbalance of these two hormones is associated with the constant urge to eat. As a result, such a hormonal disbalance can lead to the development of obesity.

#5 – Psychosocial causes of obesity

This group of causes of obesity is very broad. Namely, there are lots of different sub-causes within the psychological and social group of factors that lead to obesity (8). Those include:

  • the social status of an individual,
  • the sedentary way of life,
  • influence of the media,
  • obesity of one or both parents,
  • knowledge on the nutrition of the child’s parent(s).

In the opinion of the obesity development, psychologists, psychological factors, the influence of the family and the environment, as well as the personality structure are very important.

Obese people are often individuals who had experienced certain emotional stressful events. Scientists have proven that such situations lead to the development of reactive obesity.

Inheritance is also one of the most important co-factors in developing obesity. About 80% of obese people have a positive history of obesity in their family. However, we are not talking only about genetic inheritance here. In this particular section, we want to emphasize the psychological inheritance. We are talking about the learned or inherited patterns of parental behavior regarding nutrition and lifestyle.

#6 – Cultural influences

Some of the most important causes of obesity include the cultural influences on eating habits and physical activity. Research shows that drinking drinks with sugar and eating candies are the main culprits of obesity in the youth.

Moreover, the media challenges (TV, the Internet influence, the power of commercials) are particularly effective when it comes to the most vulnerable group – the children. Culture and education system offers very few healthy replacements. At the same time, even children are getting used to the sedentary way of life. They spend their time playing video games and working on a computer, which means they only move from one sitting position to another.

Altogether, these poor nutrition habits and lack of physical activity which are dominant in our global, contemporary way of life, lead to the development of obesity, both in children and adults (9).

#7 – Various diseases

Excessive weight contributes to a whole range of health conditions, though they are rarely its primary cause. Patients with thyroid gland disorders either lose weight or gain weight. This disorder can lead to obesity.

Similarly, Cushing’s disease, which is rare and caused by high levels of steroid hormones, leads to obesity and loss of muscle tissue at the same time (10).

People suffering from insulin resistance are in the so-called pre-diabetes stage. When they eat “wrong” food, such as candies, pasta, rice, potatoes – their body delivers too much insulin and stores all of it in fat cells. Then, their sugar levels suddenly decrease and they feel fatigued, numbness, and increased urge to eat. This is a vicious circle. Such patients should be given insulin resistance therapy to reduce the negative effects of this condition and to avoid obesity.

Moreover, obesity is associated with polycystic ovarian syndrome (PCOS) (11). The way our body works is regulated by hormones and PCOS affects our hormonal balance as well. This disbalance can affect the way our body deals with fat.

#8 – Fast food and junk food consumption

We all enjoy eating fast food, mainly French fries, burgers, fried chicken and onions, etc. However, constant consumption of food that is prepared quickly or fried in deep oil is one of the leading causes of obesity, both in children and adults (12).

Moreover, this type of food is especially dangerous when it comes to the health of our cardiovascular system. It improves the development of atherosclerosis, a serious condition that leads to stroke.

Junk food usually contains lots of carbohydrates. You must know that carbohydrates probably account for the largest portion of our daily caloric intake. Carbohydrates are a bad source of calories. The daily intake of sugar should not exceed 10%.

#9 – Skipping breakfast

Long hours of starvation and consuming large portions of food afterward are very dangerous for our body. Namely, this kind of diet tricks our metabolism in a negative way. If you skip meals, especially breakfast, your body activates the “saving” mode. It “thinks” that you don’t have enough food and it should save energy.

As a result, you can’t spend calories. Moreover, you won’t have the energy to exercise, so you will probably spend your day sitting or sleeping. You will also feel fatigued. In addition, if you often skip breakfast, you will slow down your metabolism in the long-term and this might lead to obesity (13).

Similarly, failure to consume four to five small meals during the day can also change your metabolism, digestive system, and may lead to obesity.

#10 – Lack of vegetables and fruit

Vegetables and fruit are full of fiber. You already know that high-fiber food is great for your shape. It improves digestion, metabolism, and keeps you healthy. Moreover, it provides all kinds of vitamins and minerals you need for proper functioning, work, sleep, exercising, etc.

Even though the mere consumption of vegetables and fruit will not protect you from obesity, its lack does significantly add to your chances of becoming obese (14).

Let’s talk about fiber-rich food. Most people do not consume enough fiber-rich veggies and fruits during the day. The recommended daily amount equals about 25 grams for women and 38 grams for men. Why is it so important to eat fiber-rich food? It helps control your body weight, appetite, as well as detoxification of your body. It also controls cholesterol levels and triglycerides. Fiber-rich food acts as an antioxidant.

#11 – Insufficient intake of water

Water is life. Don’t forget that scientists have proven that insufficient intake of water, combined with other causes, can reinforce and accelerate your path towards obesity (15).

Always remember that you should drink 8 glasses of water a day. The amount depends on the season, your health condition, exercising vs sedentary lifestyle, etc. However, the golden rule says eight glasses of water (around 2 liters) and we say – stick to it!

#12 – Alcohol and carbonated drinks consumption

If you are drinking socially or occasionally, don’t surprise when you notice some extra belly fat. Alcohol is actually full of calories (16)! Therefore, don’t drink alcohol at all or minimize alcohol consumption as much as you can.

The same goes for carbonated and sweetened drinks which are real calorie bombs. Moreover, these drinks negatively affect your general health, especially liver and kidneys. Stay away from them.

#13 – Lots of salt

Regardless of how many calories you intake during the day, if you consume too much salt, you can get fat and even obese, in the end. Salt negatively affects our body and changes the way the body absorbs fat (17).

In addition, salt increases your appetite. Have you ever noticed that you feel the urge to eat more even after a good meal? Next time, pay attention to the amount of salt. It might be the reason.

#14 – Lack of sleep

Lack of sleep is linked to obesity. The main culprit is not visiting the fridge during the night but in the metabolic disorder. Lack of sleep increases the ability of our body to store fat (18).

Sleep disorders and lack of sleep affect our normal, regular body rhythm, increasing the risk of a wide range of health problems, from heart disease to diabetes. Therefore, sleeping is not good only for energy savings and body regeneration, but also for the proper rhythm of many other functions.

Lack of sleep greatly affects the tendency to become obese. Lack of sleep leads to increased excretion of the hormone that controls the appetite and sense of satiety.

#15 – Certain medications (antidepressants)

It is known that drugs from the antidepressant group can cause changes in our metabolism and affect our body weight. While some antidepressants may cause an increase in our appetite and cause obesity, other types of antidepressants have a major influence on weight loss because they reduce appetite. This is why you must always consult your doctor if you notice weight gain or loss while on antidepressants.

Moreover, we can observe the vice versa effects. Namely, obesity can affect the course of treatment with certain antidepressant medications (19). This is why most doctors will suggest weight loss if you need to start treatment with antidepressants.

In addition to antidepressants, there are a number of other medicines that can increase your body weight. Those mostly include diabetes medicines, psychosis medicines, mood stabilizing drugs, corticosteroids, etc.

#16 – Stress

Stress significantly affects weight gain and weight loss. Normally, our body controls the amount of stress hormone known as cortisol.

Cortisol is a hormone that is formed in the adrenal glands. When you are under stress, it is released into the bloodstream. In addition to suppressing inflammation and regulating blood pressure, cortisol helps to maintain blood sugar levels.

The release of cortisol activates receptors found in visceral fat tissue surrounding our organs, which explains the connection between stress, cortisol, and weight gain/loss.

You should try to stay away from stress and constant exposure to stressful situations can overstimulate the hormone release, changing the way your body works and leading to obesity (20).

#17 – Excess weight gained during pregnancy

If you are planning to stay pregnant, it is very important to care about your health before pregnancy. If a woman has some excess weight from previous pregnancies or before new/first pregnancy or gains a lot of weight during pregnancy, this can increase the chances of the child’s obesity in the future.

Each pound during the pre-pregnancy period increases the risk for obesity of the baby by 4.5 percent. Similarly, children of mothers who have gained lots of weight during pregnancy have a 50 percent chance of being obese in the future. Moreover, it can lead to different health issues of the new-born (21).

Therefore, if you have some extra weight, it is a good idea to try to lose some weight before staying pregnant.

Causes of Obesity in Adults

Anyone who lacks physical activity and has unhealthy eating habits belongs to a risk group. Lack of physical activity contributes to gaining weight, and obesity makes it more difficult to move. This is a vicious circle.

World Health Organization treats obesity as a global epidemic and health problem because more and more countries accept unhealthy Western habits.

Those habits also include some other risk factors for obesity in adults. Mainly, medical specialists point out that alcohol intake, high levels of stress on a daily basis, as well as eating so-called “junk food” are among the most significant risk factors for the development of obesity (22).

Causes of Obesity in Children

Fatty cells are multiplied during two periods of growth and development: early youth and adolescence. Excessive eating in these periods increases the number of fatty cells, which is also partially genetically determined. Some of us are already born with an excess of these fatty cells.

Certainly, the role played by the parents and their general health are very important. If the parent of a three-year-old child is obese, the child (though skinny at the age of three) has a 30% chance to become obese in the future.

After adolescence, the mass of fatty cells increases, not their number, but their mass. Therefore, weight loss in adulthood decreases the size of the fat cells, again, not their number. Therefore, weight loss is much more difficult for adults who were fat in their childhood when the cells were multiplied.

In conclusion, causes of obesity in children include lack of physical activity, improper diet, excessive calorie intake, and irregular general activity and sleeping routine (23).

Risk Groups

Now when we know more on the key causes of obesity, both in adults and children, we want to talk more about risk groups and the big picture of obesity (24).

Former smokers belong to one of the risk groups for the development of obesity. The trend of weight gain always follows those who leave smoking, if they don’t turn to a completely healthy lifestyle. If they continue with other bad habits, such as eating junk food, poor nutrition, drinking carbonated drinks and other drinks containing sugar, etc., they will gain lots of weight and tend to become obese.

Nicotine accelerates metabolism, while smoking cessation, even with the same amount of eaten food, can lead to weight gain that can be significant. An important fact is that weight control is not a valid excuse for smoking. We want to point out that in the periods when people were not smoking cigarettes, there were no obesity problems either.

Workers in the night shifts (between 4 PM and 8 AM) are the second risk group. They tend to eat more and have longer vacations with sleeping during the day, which changes the way our body works and spends energy. It also causes metabolism changes and disorders. These workers are also more prone to fatigue, stress, poor sleep, etc. All of these conditions may lead to increased weight gain and obesity.

The Bottom Line

In conclusion, we can say that excessive intake of calories in combination with lack of physical activity is the obesity cause #1. It is followed by genetic predispositions, hormonal disbalance, and certain disorders and diseases.

We must not underestimate the psychosocial effects, as well as the cultural background and influence. There are also specific risk groups that are more prone to the development of obesity than other people. Those include former smokers, those who consume alcohol, as well as workers in the night shifts and people under constant stress.


(1) https://www.who.int/en/news-room/fact-sheets/detail/obesity-and-overweight
(2) https://www.ncbi.nlm.nih.gov/pubmed/28489290?dopt=Abstract&holding=npg
(3) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4890841/
(4) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4910307/
(5) https://www.ncbi.nlm.nih.gov/pubmed/23016014
(6) https://onlinelibrary.wiley.com/doi/10.1002/j.1550-8528.1995.tb00208.x
(7) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5496172/
(8) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4647643/
(9) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5644947/
(10) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2815288/
(11) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2861983/
(12) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6196377/
(13) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4310153/
(14) https://pdfs.semanticscholar.org/6f55/c9a14cd0eea03c913c20e30d6e2656bca035.pdf
(15) https://jandonline.org/article/S2212-2672(14)01505-6/fulltext
(16) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4338356/
(17) https://www.ncbi.nlm.nih.gov/pubmed/26238447
(18) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3632337/
(19) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4730324/
(20) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3428710/
(21) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2621047/
(22) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4981805/
(23) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4408699/
(24) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4859313/

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