Obesity - Causes 

Causes of obesity 

Obesity is generally caused by eating too much and moving too little.

If you consume high amounts of energy from your diet, particularly from fat and sugars, but do not burn off the energy through exercise and physical activity, much of the surplus energy is then stored by the body as fat.


The energy value of food is measured in units called calories. The average physically active man needs about 2,500 calories a day to maintain a healthy weight, and the average physically active woman needs about 2,000 a day.

This may sound high, but it can be easy to reach this limit if you eat certain types of food. For example, eating a large takeaway hamburger, fries and a milkshake can total 1,500 calories – and that's just one meal.

Another problem is that many people are not physically active, so lots of the calories they consume end up being stored in the body as fat.

Poor diet

Obesity does not happen overnight. It develops gradually over time, as a result of poor diet and lifestyle choices, such as:

  • eating large amounts of processed or fast food that is high in fat and sugar
  • drinking too much alcohol – alcohol contains a lot of calories, and people who drink heavily are often overweight
  • eating out a lot – you may be tempted to also have a starter or dessert in a restaurant, and the food can be higher in fat and sugar
  • eating larger portions than you need – you may be encouraged to eat too much if your friends or relatives are also eating large portions
  • drinking too many sugary drinks – including soft drinks and fruit juice
  • comfort eating – if you feel depressed or have low self-esteem, you may eat to make yourself feel better

Unhealthy eating habits tend to run in families, as you learn bad eating habits from your parents when you are young and continue them into adulthood.

Lack of physical activity

Lack of physical activity is another important factor related to obesity. Many people have jobs that involve sitting at a desk for most of the day. They also rely on their cars, rather than walking or cycling.

When people relax, they tend to watch TV, browse the internet or play computer games, and rarely take regular exercise.

If you are not active enough, you do not use the energy provided by the food you eat, and the extra energy you consume is stored by the body as fat.

The Department of Health recommends adults do at least 150 minutes of moderate-intensity aerobic activity, such as cycling or fast walking, every week. This doesn’t need to be done in one go, but can be broken into smaller periods. For example, you could exercise for 30 minutes a day for five days.

If you are obese and trying to lose weight, you may need to do more exercise than this. It may help to start off slowly and gradually increase the amount of exercise you do each week.

Read more about the physical activity guidelines for adults.


Some people claim there is no point in trying to lose weight because "it runs in my family" or "it's in my genes".

While there are some rare genetic conditions that can cause obesity, such as Prader-Willi syndrome, there is no reason why most people cannot lose weight.

It may be true that certain genetic traits inherited from your parents – such as having a large appetite – may make losing weight more difficult, but it certainly doesn't make it impossible.

In many cases, obesity is more to do with environmental factors, such as poor eating habits learned during childhood.

Medical reasons

In some cases, underlying medical conditions may contribute to weight gain. These include:

  • an underactive thyroid gland (hypothyroidism) – where your thyroid gland does not produce enough hormones
  • Cushing's syndrome – a rare disorder that causes the over-production of steroid hormones

However, if conditions such as these are properly diagnosed and treated they should pose less of a barrier to weight loss.

Certain medicines, including some corticosteroids, medications for epilepsy and diabetes, and some medications used to treat mental illness – including antidepressants and medicines for schizophrenia – can contribute to weight gain. Weight gain can also sometimes be a side effect of stopping smoking.

Page last reviewed: 03/06/2014

Next review due: 03/06/2016


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The 6 comments posted are personal views. Any information they give has not been checked and may not be accurate.

J0hn0000 said on 20 June 2014

Eating healthily can actually be cheaper than eating fast food / junk - lentil soup costs almost nothing and is delicious, potatoes , pasta potatoes and vegetables are not expensive and small amounts of meat are easy and healthy - making your own burger from basic mince is about the same as mass produced ones.. It's a complete apologist smokescreen that healthy eating is more expensive . Sorry to have to say this.. It's lack of will and willingness to change eating habits.

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khairat said on 17 May 2014

Great post, i found more great content about obesity risks at: http://cheapeasymeals.hubpages.com/hub/Health-Diseases-Related-to-Obesity-and-Overweight

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Mike Ospab said on 10 January 2014

Hi, eating a healthy diet and engaging in exercise are two things that need not be a significant burden on the wallet. Fresh fruits and vegetables are cheap in supermarkets and on high street markets, and a diet rich in these ingredients goes a long way towards becoming a healthy one. Sourcing your calories from primarily carbohydrates (these are the human body's preferred source of energy, as these are metabolised or stored as glycogen - a stored form of carbohydrate - long before fats, proteins, and alcohols are; the body will seek to burn off carbohydrates before trying to turn them into fat, as this is the most efficient method available to the body, even if it's only to produce dietary thermogenesis, the warming of the outer body). As for exercise: attending a gym is not mandatory. Engaging in simply physical activities even like just walking a couple of miles a day, or doing fifteen minutes worth of star jumps in your home, will promote the oxidisation of stored body fat. Please understand that your health is your responsibility, and not that of the government. As already stated, healthy fresh food is cheap and exercise is free.

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jennyrobson85 said on 21 May 2013

even if i wanted to eat healthy and do exercise its so expensive that this isn't really an option for me. the nhs and the government expect you to lose weight but they could make it a lot easier by making healthy food, gym memberships etc cheaper.

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paul parmenter said on 26 January 2013

Shame that what is supposed to be s public service advertisement by a body that is funded by taxpayers, should stoop to cheap and totally gratuitous misandry - depicting the man as stupid and the woman as superior. Presumably the NHS has done so in order to fall in line with so many ads that do exactly the same. Or maybe the NHS just doesn't have the imagination to break out of that abysmal and insulting stereotyping.

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2305 said on 30 October 2012

You state that coc can cause wt gain but if the link for coc is followed it say there is no evidence that the pill causes wt gain!

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