According to the NHS, around 1 in every 4 adults in the UK are living with obesity, a term which describes the carrying of excess body fat. The most common measure of obesity is the body mass index (BMI). A BMI over 25 is considered overweight and over 30 is obese. 

Obesity comes with risks. In 2019, high BMIs caused some 5 million deaths related to non-communicable diseases like strokes, heart disease and cancers, the World Health Organisation (WHO) says.

But what causes obesity? It’s not as straightforward as you might think. 

What Are the Causes of Obesity?

Obesity carries a stigma. Many people see obesity as a personal and moral failure, rather than a health issue.

If you carry excess weight, it doesn’t mean you’re lazy or lack willpower. Despite the stigma, how much you weigh is not always within your control – although there might be things you can do to help shed excess weight.

In this article, we explain the four most common causes of obesity. And suggest ways you might be able to overcome challenges to lose weight and body fat:

  • Underlying health conditions
  • Certain medications
  • Consuming too many calories
  • Not getting enough exercise

Underlying Health Conditions

Certain health conditions have been found to cause weight gain, which can lead to obesity.

Common signs of an underactive thyroid gland include weight gain, as well as tiredness and feeling depressed. An underactive thyroid is usually treated with daily hormone replacement tablets, called levothyroxine, which raise thyroxine levels.

Weight gain is also one of the main signs of Cushing’s syndrome, which is caused by excess cortisol in the body. In fact, nearly all patients with the syndrome are obese. Symptoms include an increase in body fat on the chest and tummy, a build-up of fat on the back of your neck and shoulders and a red, puffy, and rounded face.

PCOS is an obesity-related condition in women. Obesity contributes towards the development of PCOS. The condition can also contribute to weight gain and make it harder to lose weight.

Speak to your GP if you think you have one of these health conditions.

Certain Medications

All medications have side effects. For some medications, weight gain is one of them. The medications most likely to cause weight gain include:

  • Steroids: Used to treat inflammatory conditions, including asthma, cancer and arthritis, steroids can cause weight gain. One survey of 2,167 long-term users found weight gain to be the most common self-reported side effect, affecting 70% of patients.

  • Diabetes Medication: Some diabetes treatments have been linked to weight gain. These include insulin and sulphonylureas (which stimulate the pancreas to produce more insulin).

  • Epilepsy Medication: Some anti-epileptic drugs are associated with weight gain. These include gabapentin, pregabalin, valproic acid, and vigabatrin.

  • Antidepressants: A study from King’s College London found that patients prescribed any of the 12 most commonly used antidepressants were 21% more likely to gain weight than those not taking the drugs. For patients of a ‘normal’ weight, the risk of moving to either the overweight or obese categories increased by 29%.

Adopting a healthier lifestyle can help minimise the risk of weight gain on some of these medications. Experts recommend patients taking antidepressants eat a healthy, balanced diet, quit smoking, reduce alcohol consumption and exercise regularly.

If you’re concerned about weight gain you’re experiencing on your medication, you can also talk to your doctor. They might be able to recommend alternative medication. Do not stop taking your medication without first consulting a healthcare professional as this could have serious effects on your health.

Consuming Too Many Calories

If you’re struggling to lose weight, it could be because you’re eating more calories than your body needs. When this happens, you don’t burn off that energy and your body stores it as fat.

In order to lose weight, the NHS recommends you reduce your calorie intake by approximately 600 calories per day. The recommended daily calorie allowance is 2,500 for men and 2,000 for women. So, to lose weight, the average man would consume 1,900 calories and the average woman would consume 1,400 calories.

But you may need to adjust the number of calories you eat, depending on your activity levels, body size and age to achieve a calorie deficit.

You can use weight loss treatments alongside lifestyle changes to help you reach your goals. Weight loss injections like Mounjaro and Wegovy suppress your appetite, helping you consume fewer calories. And pills like Orlistat and Alli support weight loss by stopping the body from absorbing 30% of fat from meals.

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Not Getting Enough Exercise

Physical activity will help you burn some of the calories you get from food while increasing your metabolic rate, helping you burn more calories.

The Department of Health and Social Care recommends adults over 19 do at least 150 minutes of moderate intensity exercise or at least 75 minutes of vigorous intensity exercise per week (or a combination of both).

Moderate intensity activity is activity where your breathing increases, but you’re still able to talk. This could include swimming, a brisk walk and cycling. Vigorous activity, where you find it hard to talk, could include running, taking the stairs and sports like tennis or football.

If you don’t think you’re getting enough exercise, but you’re short on time, there are ways to “sneak” it in. You could take the stairs instead of the lift or park in the furthest spot in the car park and walk.

And remember, something is better than nothing. So find an exercise you enjoy – like a free exercise video or a run around the park – and do as much as you have time for. Whether that’s 20 minutes or one hour.

Key Takeaways

  • Obesity increases the risk of non-communicable diseases like heart disease, stroke, and certain cancers. But it isn’t just caused by overeating, and it’s not a personal or moral failure. 
  • Conditions like hypothyroidism, Cushing’s syndrome, and PCOS can cause weight gain.
  • Certain medications, including steroids, diabetes treatments, epilepsy drugs, and antidepressants, can lead to weight gain as a side effect.
  • Consuming more calories than the body needs leads to fat storage, contributing to weight gain and obesity.
  • Not getting enough exercise lowers the number of calories you burn, making it easier to gain weight.

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References

World Health Organization (2020). Obesity. [online] WHO. Available at: https://www.who.int/health-topics/obesity.

Department of Health and Social Care (2023). Physical activity guidelines. [online] GOV.UK. Available at: https://www.gov.uk/government/collections/physical-activity-guidelines.

Liu, D., Ahmet, A., Ward, L., Krishnamoorthy, P., Mandelcorn, E.D., Leigh, R., Brown, J.P., Cohen, A. and Kim, H. (2013). A practical guide to the monitoring and management of the complications of systemic corticosteroid therapy. Allergy, Asthma & Clinical Immunology, [online] 9(1), p.30. doi:https://doi.org/10.1186/1710-1492-9-30.

www.kcl.ac.uk. (n.d.). King’s study finds link between antidepressant use and weight gain | Website archive | King’s College London. [online] Available at: https://www.kcl.ac.uk/archive/news/sphes/kings-study-finds-link-between-antidepressant-use-and-weight-gain.

Editor (2019). A number of widely prescribed diabetes medications have been linked with increased weight gain. [online] Diabetes. Available at:https://www.diabetes.co.uk/weight/weight-gain-on-medication.html.

Antel, J. and Hebebrand, J. (2011). Weight-Reducing Side Effects of the Antiepileptic Agents Topiramate and Zonisamide. Handbook of Experimental Pharmacology, pp.433–466. doi:https://doi.org/10.1007/978-3-642-24716-3_20.

Jallon, P. and Picard, F. (2001). Bodyweight Gain and Anticonvulsants. Drug Safety, 24(13), pp.969–978. doi:https://doi.org/10.2165/00002018-200124130-00004.

Jallon, P. and Picard, F. (2001). Bodyweight Gain and Anticonvulsants. Drug Safety, 24(13), pp.969–978. doi:https://doi.org/10.2165/00002018-200124130-00004.

NIH (2021). What causes obesity & overweight? [online] National Institute of Health. Available at: https://www.nichd.nih.gov/health/topics/obesity/conditioninfo/cause.