What causes obesity?

Obesity is widely recognised as a chronic disease. It’s influenced by lots of factors, and many of them are out of your control ^{1 2 3 4}.

One cause of obesity is an imbalance between what food you eat and how much movement you get.

Long daily commutes, desk jobs and communities with less green space make it more difficult to get enough exercise⁵.

In our modern lives, there are more energy-dense foods available which are often higher in sugar and fat. These foods are often cheaper, easier to access and more convenient for people leading busy lives⁵.

Chemical sensors in our blood called hormones give us a signal when we’re hungry, so we eat, and when we’re full, so we stop⁶.

For people who are obese, these hormones don’t work as they should, meaning you have to eat more before you feel full⁶. These hormones make it harder for you to lose weight and keep it off⁷.

Your genes play a big role in whether you will develop obesity. Studies on twins who grew up in different homes found their genes had a bigger impact on whether they had a higher BMI⁸. In this study, they found environmental factors had little impact.

This may sound disheartening, but it doesn’t mean you should give up on losing weight. It just shows that obesity is not your fault.

There are certain cultural backgrounds that are more likely to develop obesity than others. In Australia, 3 in 4 Aboriginal or Torres Strait Islander adults are overweight or obese⁹.

There are many reasons for this, including a change in diet from more natural based foods to processed foods and increased likelihood of living in lower socioeconomic areas, rural and regional areas, which all have higher rates of obesity¹⁰.

Stress is a natural response to challenging situations. However, long-term stress can be a problem for your health.

When you’re stressed, cortisol levels rise in your blood, which increases your appetite. When you have higher cortisol levels, you’re more likely to choose less healthy foods¹¹ and then your body metabolises the food slower, leading to weight gain¹².

How long you sleep, and the quality of your sleep can also be a risk factor of obesity¹³.

Studies have found people who often get less sleep than they need have hormone changes that increase their appetite, leading to weight gain¹⁴.

Doing shift work at night has also been found to be a risk factor for obesity¹⁵.

Some medicines may affect your weight, particularly if you’re on them for a long time. Some medicines might make you feel hungrier, others might affect your body’s metabolism.

If you suspect your medicine is contributing to your weight gain, it’s important not to stop taking them. Talk to your doctor about what the best approach is in your situation.

Where you live can have a direct impact on your weight. Advertising, access to fresh fruit and vegetables and support from your government, workplace and community can affect the food choices you make and how much exercise you’re able to do⁵.

For example, in Australia, 38% of adults in the lowest socioeconomic areas were obese, compared to 24% in the highest.⁹

People living in rural and regional areas are also more likely to be overweight or obese compared to those in cities. Reasons for this include higher prices for fresh food, lower quality drinking water and less access to sporting grounds and places to exercise¹⁰.