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.

A man at his laptop at work wondering what causes obesity

Food intake and exercise

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.

Type of food

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.

Appetite signals and hormones

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

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.

Your cultural background

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 management

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.

Quality and quantity of sleep

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.

Prescription medications

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.

Environmental factors

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.

The negative impact of obesity
1 RACGP. Obesity prevention and management position statement 2019. Available at https://www.racgp.org.au/FSDEDEV/media/documents/RACGP/Position%20statements/Obesity-prevention-and-management.pdf, accessed December 2021.

2 Caterson I, et al. Gaps to bridge: Misalignment between perception, reality and actions in obesity, Diabetes Obes Metab 2019; 21(8): 1914–24. https://pubmed.ncbi.nlm.nih.gov/31032548/

3 National Health and Medical Research Council (2013). Clinical practice guidelines for the management of overweight and obesity in adults, adolescents and children in Australia. Available at https://www.nhmrc.gov.au/about-us/publications/clinical-practice-guidelines-management-overweight-and-obesity, accessed September 2019.

4 Casazza K, et al. Myths, Presumptions, and Facts about Obesity.N Engl J Med 2013; 368:446-454 https://www.nejm.org/doi/full/10.1056/NEJMsa1208051

5 World Health Organisation Obesity and Overweight Fact Sheet, 9 June 2021 Available at https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight. December 2021.

6 Klok, M.D., Jakobsdottir, S. and Drent, M.L. (2007), The role of leptin and ghrelin in the regulation of food intake and body weight in humans: a review. Obesity Reviews, 8: 21-34. https://doi.org/10.1111/j.1467-789X.2006.00270.x

7 Sumithran P, Prendergast L, Delbridge E et al Long-Term Persistence of Hormonal Adaptations to Weight Loss N Engl J Med 2011; 365:1597-1604 DOI: 10.1056/NEJMoa1105816 https://www.nejm.org/doi/full/10.1056/nejmoa1105816

8 Stunkard AJ, Harris JR, Pedersen NL, McClearn GE. The body-mass index of twins who have been reared apart. N Engl J Med. 1990;322(21):1483-1487. doi:10.1056/NEJM199005243222102 https://www.nejm.org/doi/full/10.1056/nejm199005243222102

9 Australian Institute of Health and Welfare (2020) Overweight and obesity: an interactive insight., AIHW, Australian Government, accessed 15 December 2021 https://www.aihw.gov.au/reports/overweight-obesity/overweight-and-obesity-an-interactive-insight/contents/what-is-overweight-and-obesity

10 Australian Government Department of Health Factors that Affect Weight Fact Sheet, 29 July 2021. Available from https://www.health.gov.au/health-topics/overweight-and-obesity/factors-that-affect-weight. Accessed December 2021

11 Zellner DA, Loaiza S, Gonzalez Z, et al. Food selection changes under stress. Physiol Behav. 2006;87(4):789-793. doi:10.1016/j.physbeh.2006.01.014 https://pubmed.ncbi.nlm.nih.gov/16519909/

12 Kiecolt-Glaser JK, Habash DL, Fagundes CP, et al. Daily stressors, past depression, and metabolic responses to high-fat meals: a novel path to obesity. Biol Psychiatry. 2015;77(7):653-660. doi:10.1016/j.biopsych.2014.05.018 https://www.biologicalpsychiatryjournal.com/article/S0006-3223%2814%2900385-0/fulltext

13 Beccuti G, Pannain S. Sleep and obesity. Curr Opin Clin Nutr Metab Care. 2011;14(4):402-412. doi:10.1097/MCO.0b013e3283479109 https://pubmed.ncbi.nlm.nih.gov/21659802/

14 Taheri S, Lin L, Austin D, Young T, Mignot E. Short sleep duration is associated with reduced leptin, elevated ghrelin, and increased body mass index. PLoS Med. 2004;1(3):e62. doi:10.1371/journal.pmed.0010062 https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.0010062

15 Brum, M.C.B., Dantas Filho, F.F., Schnorr, C.C. et al.Night shift work, short sleep and obesity. Diabetol Metab Syndr12, 13 (2020). https://doi.org/10.1186/s13098-020-0524-9