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Morbid obesity causes, complications, and effective treatments available

You're far from alone if you're struggling to lose weight.

Written by
Vivienne Pearson
Medically reviewed by
Dr Matthew Vickers
Last updated
April 29, 2024
min read
Morbid obesity causes, complications, and effective treatments available
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Morbid obesity is diagnosed to patients with a Body Mass Index (BMI) of >40. While not always easy to address, treating morbid obesity is possible with safe medical intervention.

Two-thirds of Australian adults are overweight or obese, so it's safe to say you're far from alone if you too are struggling to lose weight.

Obesity, and weight in general, is not merely an Australian problem. The World Health Organisation reports that obesity is on the rise across the globe, including in the developing world, and just about everywhere, impacts are felt on a societal level, with health systems struggling as more of us develop obesity-related conditions.

This risk is especially high for people who meet the criteria for being morbidly obese, as the excess weight can prompt additional medical conditions that are generally harder, though not impossible, to treat.

The good news is body fat can be lessened, and with weight loss, these health risks can go away. Through a combination of diet, exercise and medical assistance, it is certainly possible to lose weight, keep it off, and rewrite lifestyle habits for long-term health.

Read on to find out more about what morbid obesity is, what complications can arise, and what treatment options are available.

What is morbid obesity?

Morbid obesity is a condition diagnosed in people with a body mass index (BMI) of 40 or higher. Morbid obesity is also sometimes referred to as clinically severe obesity or class 3 obesity.

In simple terms, a person is considered obese when they have a high percentage of body fat, usually as a result of their body storing unused calories as fat when these are not used for energy expenditure.

What causes morbid obesity?

Obesity and morbid obesity are the result of having too much stored fat in the body. For many people, severe obesity is the eventual result of eating more calories than the body can physically use up as energy.

The calories we consume are used to keep every part of the body functioning — from the digestive system to the legs that walk us to work. But when we consume more calories than our body can use up, this extra energy ends up stored as fat. It's these extra fat stores that result in obesity.

As for why this actually happens, the reasons can be simple or quite complex.

Lifestyle factors

As a society, our lifestyles as a whole have become more sedentary. Desk-based and other inactive jobs like truck or Uber-driving can make it challenging to get the recommended amounts of physical activity.

What are those recommendations? Firstly, 2-5 hours of moderate activity a week, like walking, swimming, golfing or even mowing the lawn. Then, add in 1.5-2.5 hours of intense activity, like team sports or jogging.

Our access to nutritionally-deficient, high-fat foods has also increased with fast food becoming more and more accessible in comparison to nurtient-rich meals.

Genetic and environmental factors

The genetic lottery can also deal you a challenging hand, with recent evidence finding genetics can play up to an 80% role in the way our body's approach weight.

And, there's no doubt that it's harder to maintain healthy eating habits while dealing with other environmental factors, such as stress, mental illness, poor sleep quality, and physical injuries or illness.

Hormonal imbalances or prescribed medication can contribute to, or directly cause, weight gain.

Diagnosing morbid obesity

Morbid obesity is diagnosed by medical professionals when your body mass index (BMI) is over 40.

To calculate your BMI the simple way, you can an online calculator like this one from the Heart Foundation or reference the BMI ranges below and their obesity classifications:

  • <19 Underweight
  • 19-25 Ideal BMI
  • 25-30 Overweight
  • 30-35 Obese (Class I)
  • 35-40 Severely Obese (Class II)
  • >40 Morbidly Obese (Class III)

If you're keen to understand the algorithm, here's an explanation:

BMI = Your weight (in kilograms) divided by the square of your height (in metres).

So, if you are 180cm tall (1.8m) and weigh 100kg, the calculation would be:

100 / (divided by) 1.8²

= 100 / 1.8x1.8

= 100 / 3.24

= 30.86.

Your BMI is 30.86.

This BMI would put a person into the official range for obesity (the term for a BMI between 30 and 34.9).

If you are the same height (180 cm) and instead weigh 132kg, your BMI would be 40.7, meaning you would be considered 'morbidly obese'.


BMI is a helpful measurement and a fine first step, but it's not perfect. Assessing the impact of your weight is not a one-size-fits-all undertaking.

For a start, your weight is only an estimation of your amount of body fat. A body-builder is an example of someone who will be heavy (due to all that muscle) and therefore will have a high BMI, but only have a small amount of body fat.

The body mass index measurement also isn't very sensitive to natural variations across people of different ages or ethnicities.

Other tests that might be helpful include:

Waist circumference: Research shows that men are at greater risk of health problems if their waist measures more than 94 centimetres around.

Skinfold test: A doctor can gauge your body fat percentage by taking measurements of your skin when 'pinched' between callipers. Or, they can use a test that uses bioelectrical signals.

Medical tests: Other markers of weight-related health are blood pressure, blood sugar and cholesterol levels.

Morbid obesity complications

Morbid obesity affects many of the systems and function in our bodies, from blood flow and breathing to sleep and sex. It follows then that having a body mass index of over 35 puts people at risk of a range of other health concerns.

These other health concerns may start as a complication of excess weight but are real conditions in themselves, negatively affecting quality of life. Some of these conditions come with real mortality risk, reducing life expectancy.

Here are some of the health issues that can result from severe obesity:

Type 2 diabetes

Almost 1 million Australians report having type 2 diabetes, according to the Australian Institute of Health and Welfare, and a further 2 million have prediabetes and are at a high-risk of developing diabetes.

Being overweight or obese increases the chances of developing significantly because when the body has excess weight, our cells become less sensitive to insulin, which is a hormone released from the pancreas. This can lead to insulin resistance, resulting in diabetes.

Sleep apnoea

Sleep apnoea is a condition related to snoring that causes people to stop breathing hundreds of times a night. Sleep apnea results in poor sleep quality and all the negative effects of being sleep deprived (brain fog, drowsiness, poor concentration).

Sleep apnoea is a result of obesity, and it's caused by excess fat carried in the neck, which contributes to the airway collapsing as you breathe.

Cardiovascular disease

Excess weight puts pressure on the body's system that carries blood around the body. People who are morbidly obese are at greater risk of high blood pressure, heart disease and stroke.

Cardiovascular disease or CVD is a major cause of death in Australia, responsible for causing one in four deaths, according to the Heart Foundation. On average, 118 Australians die from CVD each day, and CVD costs the Australian healthcare system $5 billion a year.

Musculoskeletal problems and pain

Carrying extra weight makes it hard for your body's muscles and joints to function at their full ability. Some obese patients experience significant pain as a result, and this is then exacerbated by decreased mobility in their limbs and undertaking less physical activity than is recommended.

This can make it hard to develop good exercise habits and undertake vigorous exercise needed for losing weight.


Known as OA, osteoarthritis is the gradual loss of cartilage in the joints along with inflammation, causing restricted movement and pain. It's a relatively common disorder, especially in older patients' hands, knees and hips, likely caused as a result of the body being unable to repair tissues in the joints as it usually does.

Excess weight increases the risk of osteoarthritis due to the strain it puts on weight-bearing joints like the back, knees, hips and ankles.

Greater impact of disease such as COVID-19

There is evidence to suggest that severe obesity can put you at a higher risk of hospitalisation from viruses like COVID-19. The upside of this whole-body effect of severe obesity is that, as you lose weight, you'll start to see real benefits in every aspect of your body and life.

Seemingly untreatable pain can disappear once your skeleton and muscles no longer have to support as much weight. A restful night will be back on the agenda once excess fat in the neck is no longer obstructing your airway during sleep. And your mood and confidence will also be on the rise.

Treating morbid obesity

The treatment for morbid obesity is losing weight, but any good medical practitioner will understand that this can be really challenging for people living with morbid obesity.

While diet and exercise are often put forward as the first approach for losing weight, for people with obesity or morbid obesity, it's not always the most practical, especially when patients have struggled to lose weight multiple times over a number of years.

If that's the case, a doctor should really be taking a look into what's causing the weight gain and work to find a viable solution that helps a patient get to a healthy weight range and stay there.

First, a healthcare practitioner should assess and treat any underlying or consequential health concerns, as well as help the patient set realistic goals for weight loss. Intervention from other specialty areas of medicine can also be helpful for addressing weight gain in a holistic way.

Dietitians can help you learn which foods to eat more, and less of.

Psychologists can also help you make cognitive and behavioural changes, and help you learn stress management techniques for alternatives to eating in times of pressure.

A personal trainer or physiotherapist will be able to help you build more activity into your life and start stronger exercise in a way that is safe and hopefully enjoyable.

A health coach can be an ideal person to assist you with all aspects of your weight loss journey, and keep you motivated to reach your goals.

Morbid obesity treatments

When lifestyle changes don't cut it, medical assistance can go a really long way for helping people successfully lose weight, and keep it off for good.

With a trusted medical professional, you may wish to consider medical intervention.

Weight loss program

Specialist-designed weight loss treatments, health coaching and meal replacement shakes can all help you reach your weight loss goals in a more sustainable and encouraging way.

That's why Pilot's Metabolic Reset Program incorporates all of these treatments into one effective weight loss program. Our program gives you access to clinically-proven treatments that target the body’s metabolic patterns as well as health coaching and one-on-one goal setting with an Australian practitioner so you have all of the tools to improve your health.

Weight loss surgery

Weight loss surgery is never a first-line plan, but 'bariatric surgery', like gastric banding (which changes the stomach's size) or gastric bypass surgery (which changes how food is digested) can be a positive intervention for some patients with severe obesity.

Your doctor can also help work out whether other medical issues are causing or contributing to obesity. At the time time, health professionals can make sure any obesity-related health conditions are being treated and managed.

The difference between being obese and morbidly obese

Obesity is defined as someone who has a body mass index (BMI) between 30 and 34.9. The category of morbid obesity is when the person's BMI is above 40.

Regardless of where on this index a patient fits in, losing weight in order to fall within a healthy BMI range is possible with the right level of safe medical intervention.

Photo credit: Getty Images

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