Obesity, causes, symptoms, risk factors and complications

Doctor measuring a man's hip-to-waist ratio

According to the World Health Organization, more than 340 million children and teenagers between the ages of 5 and 19 were obese in 2016. Also, as of 2016, over 650 million adults aged 18 and older were obese.

A larger number of the world's population live in countries where obesity and being overweight kill people more than being underweight.

While many people find it challenging to control their body size, there are things one can do to reduce the risk of being obese. Adopting certain lifestyle and dietary changes helps prevent excessive weight gain or obesity.

What is obesity?

Obesity or overweight is the excess or abnormal accumulation of fat such that it can pose a serious health risk.

Being overweight is usually caused by extra body fat. However, there are cases where the overweight is due to extra muscle, increased bone density, or even water. In case of obesity, it is usually due to excess body fat.

But how do you know if you are obese?

Using the Body Mass Index, you can tell if you are underweight, overweight, or have a normal body weight. The body mass index (BMI) measures your body size using your body weight and height.

The higher your BMI, the higher your risk of developing complications as a result of being overweight or obese. According to the Centres for Disease Control and Prevention (CDC), obesity in adults is defined as having a BMI of 30 or more.

This means to find out your weight, you have to calculate your BMI, after which you use the BMI table, which shows how obesity is classified, to check which category your weight falls into.

Many studies have linked obesity with an increased risk of developing certain life-threatening diseases like heart disease, high blood pressure, cancer, and type 2 diabetes.

Obesity classification

Using the BMI result, obesity can be classified in adults, as shown in the table below.

How obesity is classified



18.5 or under


18.5 to <25.0

Normal weight

25.0 to <30.0


30.0 to <35.0

Class 1 obesity

35.0 to <40.0

Class 2 obesity

40.0 or over

Class 3 obesity (mobid or extreme obesity)

The BMI limitation

For now, the BMI is the standard way of measuring body weight; however, it is notable to add that this weight metric has its limitations.

It doesn't take into consideration certain factors that can affect BMI and body fat, such as gender, age, muscle mass, and even ethnicity.

The CDC took note of this and said: "Factors such as age, sex, ethnicity, and muscle mass can influence the relationship between BMI and body fat."

In addition, BMI has been unable to differentiate between excess fat, bone mass, or muscle. It also doesn't show how fat is distributed in individuals.

However, despite these limitations, BMI has offered a great way to measure body size and is widely used today to classify obesity.

Causes of obesity

The major cause of obesity is eating more calories than the body burns daily. Accumulating calories can cause weight gain, ultimately leading to obesity.

However, while consuming too many calories and a sedentary lifestyle are the major causes of obesity, there are other causes that might be beyond your control.

Other causes of or risk factors for obesity are:

  • Genes: Genetic factors can affect how the body metabolizes food and converts it to energy. It also affects how fat is stored and thus can be linked with obesity.
  • Pregnancy: During pregnancy, women usually gain additional weight. This weight gained during pregnancy is usually difficult to lose and might likely lead to obesity. Pregnancy is one of the reasons why it is harder for women to lose weight.
  • Insufficient sleep: Some studies have linked insufficient sleep to weight gain. When you don't get enough sleep, it can cause hormone changes, which can induce hunger and craving for high-calorie foods.
  • Certain medical conditions: Some medical conditions can cause weight gain, which can lead to obesity. Examples of diseases that can predispose to obesity include polycystic ovarian syndrome (PCOS), Cushing syndrome, osteoarthritis, and hypothyroidism.
  • Old age: When you get older, you start losing muscle mass. You experience a slower metabolic rate and tend to be less active. These factors make it easier for people to gain weight as they grow older.

Symptoms of obesity

The first thing you notice about an obese person is their excessive body fat or large body size. Aside from the obvious sign of obesity, which you notice in the person's appearance, there are some symptoms obese people may experience.

Some common symptoms of obesity include:

  • Shortness of breath
  • Snoring
  • Sweating
  • Trouble sleeping
  • Fatigue
  • Pain
  • Inability to carry out some simple physical activities
  • Pain (particularly in the joints and back region)
  • Psychological and emotional impacts such as depression and low self-esteem
  • Eating disorders

Complications of obesity

Obesity goes beyond weight gain. Excessive body fat puts a strain on the bones and can cause harm to the internal organs. It can induce inflammatory reactions, which might be a risk factor for cancer.

Research on obesity complications has shown that it can cause some serious health problems or worsen them. Some health complications of obesity include:

  • Type 2 diabetes
  • High blood pressure
  • Heart diseases
  • Stroke
  • Fatty liver disease
  • High cholesterol
  • Arthritis
  • Certain cancers, e.g., endometrial, breast, and colon
  • Sleep apnoea

How to prevent obesity

There are some lifestyle changes and mindful practices that can help with obesity. Even though there has been an increase in obesity and related diseases in the last few decades, it is a relief to know that there are things you can do to prevent obesity or excessive weight gain.

The two major ways to prevent obesity are by making dietary changes to incorporate the right food choices and adopting a physically active lifestyle.

In order to maintain a healthy weight, you don't make only short-term dietary changes. You would need to fully adopt a lifestyle that includes eating healthy and being actively involved in physical activities.

Certain dietary plans, such as ketogenic, low-carb, paleo, vegan, and even intermittent fasting, have shown promise in weight management and loss.

However, you should know that there is no perfect diet for everyone. What works for someone else might not work for you. Thus, it would be best to choose a diet and lifestyle that is ideal for you.

An ideal dietary plan should be one that works effectively for you and that you can stick to in the long term.

Below are some simple things you can start doing now to prevent obesity:

  • Avoid eating processed foods containing lots of refined sugar and salt, e.g., pastries, baked foods, fries, chips, and soda.
  • Avoid consuming unhealthy fats (saturated and trans fat); instead, stick with unsaturated fats, which are more healthy.
  • Get physically active. Develop a workout routine that involves exercising at least thrice a week and stick to the routine.
  • Make sure you get enough sleep.
  • Relax more often. Stress has been linked with obesity as it increases cortisol levels (a stress hormone), which can ultimately lead to weight gain.
  • If you are concerned about weight-related health issues, it will help to pay regular visits to your doctor.