Causes of obesity

What causes Obesity?

Is it just a mismatch between how much we eat and exercise? ‘Obesity’ is a medical term used to describe an individual who is excessively overweight, and this is defined as a person with a Body mass index (BMI) score of more than 30…BMI is used so your weight can be correlated directly to your height to determine what is healthy for you. There are some limitations with using BMI scores as people who are muscular, with little fat, sometimes may also appear to have a higher BMI than expected.

When you eat, your body absorbs energy (calories) from your food and this energy is then used to fuel your day to day activities, such as a morning jog or your walk to work. However, when an imbalance is created where you eat more ‘energy’ than you burn off over time, your body stores the excess ‘energy’ or calories as fat.

If this imbalance between the amount of energy consumed versus used up is maintained, fat accumulation can become severe enough to start affecting your health and can cause serious health problems. So what’s causing this imbalance, and why is the UK currently in an ‘obesity epidemic’?


Some very rare genetic conditions can cause obesity along with multiple other symptoms. But how do genetics affect the majority of us? Well, some individuals may be more inclined to develop obesity due to their genetic makeup.

Research has found similarities between children’s weights and the weight of their parents. This suggests that obesity may run in the family as people with obese parents are more likely to develop obesity themselves, although this might not just be down to genetic factors, as the type of food eaten and behaviours around food are influenced significantly from an early age by our parents.

We’ve all heard about those people who don’t seem to put on weight and claim to have a high metabolism, and there may be some truth that genes help to eliminate excess calories in individuals.

Further work has pinpointed certain genetic factors that influence hunger and hence might predispose a person to an increased appetite therefore having a higher chance of developing obesity.

Genes may increase your susceptibility to the development of obesity but they are certainly not the main cause.

Lifestyle factors

The development of obesity is generally a slow process, dependent on your lifestyle habits. But what everyday choices contribute to the energy imbalance that leads to accumulation of fat, and ultimately obesity?

Poor Dietary Choices

  • Processed foods: These are high in sugars, refined carbohydrates which are quickly broken down into sugar and also have a high trans-fat content. Sugar is a cause of fat accumulation as if it does not need to be used immediately as a form of energy, it needs to be stored. Excess sugar in the body will lead to accumulation of fat to store this excess energy.
  • Overeating: Especially if you are eating lots of simple carbohydrates (i.e. ones that break down into sugar quickly)
  • Sugary drinks: Consuming high amounts of fruit juices or soft drinks
  • Comfort eating: Sometimes, we eat food to help deal with stress or other mental problems as it makes you feel better in the short term. It is due to the relationship between sugar releasing hormones and the body exerting a pleasure response as a result.
  • Alcohol: beer and other alcoholic drinks usually contain extra hidden calories that we don’t factor in.


You may have noticed above that it’s not just the intake of fat that is the cause of obesity, but it is the accumulation of excess energy that the body is unable to use. This is why sugar has been implicated as one of the biggest nutritional factors in causing obesity. The sugar that is absorbed and not used is put into storage into the body and the most efficient way for the body to store excess energy is in fatty tissue.

It’s not easy to change dietary habits, and sometimes people do not realize some of their good and bad habits. If you’re struggling to lose weight often it can be helpful to get further nutritional advice from a doctor, dietitian or a suitably qualified nutritional therapist.

Low Physical Activity

Many jobs in the modern world often lead to sitting at a desk of the majority of your day. People are increasingly relying on cars or public transport to get to and from work. We, as a nation and globally have developed lifestyle habits that do not use calories which include sitting on the sofa to watch TV, using our phones for entertainment or playing video games.

These common habits mean that many people spend the majority of their time being physically inactive, and hence not burning or using the calories they have eaten. By engaging in more physical activity we reduce our risk of not just obesity but also other diseases too such as type 2 diabetes.

You should aim to exercise a minimum of 2.5 hours (150 minutes) per week, not just to help prevent weight gain, but as part of maintaining a healthy lifestyle. Recent studies suggest the optimal exercise per week is actually 5 hours (300 minutes) per week, which of course may not be achievable, and certainly most of the UK isn’t achieving this amount of activity.

A variety of cardio and weight bearing exercise is ideal. If you have been struggling to lose weight, it may be worth seeking advice of a health professional or suitably qualified weight loss professionals including those who provide weight management classes or individual coaches. Often this helps to improve the exercise you’re doing and get the most out of the time you put in to exercise.

The Doctor Service fully recommends dietary and lifestyle methods as the main way to help manage weight loss, however supplements such as Orlistat may help. Other methods of weight loss that have been reported such as methods to attempt to increase metabolism of the body we do not advocate at all and could be putting your health at risk.

Gut Flora

The human gut is filled with trillions of microorganisms, referred to as the ‘Gut Flora’. They live inside our body, and there are many benefits of having these microorganisms. One of these benefits are that they help to process and extract energy from what we eat. The importance of the gut flora is still not fully understood, however, it is a critical component that determines our metabolism and weight.

Depending on what we eat, this alters the growth of different types of desirable microorganisms. Some may protect us from excessive weight gain by decreasing the number of calories absorbed in our gut. There is ongoing research into the use of probiotics to help with weight management but we cannot provide any further advice on this currently. This highlights the increased importance of maintaining a healthy diet as it both provides the correct nourishment for the body as well as promoting the growth of desirable microorganisms.


Sleep is extremely important but what’s it doing here? We know less about the side effects of decreased or poor quality sleep but studies have now linked poor quality sleep as a risk factor for obesity. Sleep is incredibly important as it sets a rhythm known as a biological clock. The body uses this clock to know when to release hormones and carry out bodily functions.

A lack of sleep has shown to disrupt levels of important hormones, such as leptin (‘the satiety hormone’), that may lead to increased hunger and appetite. Hence, putting the sleep deprived individual at an increased risk of developing obesity.


A relationship between stress, particularly chronic stress, and obesity has been found. Current studies, focusing on animals, have discovered the role of the HPA (hypothalamo-pituitary) axis is a system that allows the brain to control certain hormones. There is a role in these hormones in the development of obesity. Chronic stress disrupts the brains control over certain hormones, via the HPA axis, which consequentially may increase the risk of developing obesity.

Research is ongoing to define the exact role of the HPA axis in obesity so that it can begin to develop new obesity treatments.


Aside from improving your diet and increasing the amount you exercise (which are the first steps to treating obesity), there are also anti-obesity medications and treatments available.

Orlistat is an advocate of healthy living and lifestyle to help prevent and manage obesity. However, Orlistat (Xenical) has been found to help to reduce weight further alongside dietary and weight changes. The graph below shows how orlistat can help with weight loss – including keeping the weight off.

Orlistat is a prescribed drug that acts on your body by preventing fat absorption. Therefore, on eating foods your body will remove the fatty components of the foods as faeces. It helps you to make the dietary changes required, and is useful in the short term. Orlistat does not provide a cure to obesity but will help with weight loss.

In a review by the Journal of the American Dietetic Association in 2016, very-low-energy diets were associated with weight gain very quickly after achieving fast weight loss. Orlistat (Xenical) was much more effective with sustaining weight loss compared with diet and exercise alone.


In extreme cases of obesity or where other measures have failed, surgery may be an option. Bariatric surgery, also known as ‘weight loss surgery’, is a general term used to describe several subtypes of obesity surgery.

Depending on the patient the most appropriate procedure will be selected. Bariatric surgery works by either reducing the size of the stomach, so that you feel fuller after eating less food. Or by reducing your ability to absorb all your food so that some of the calories are excreted in your faeces.

Bariatric surgery is not without its drawbacks. You often need to be on lifelong follow up and extra vitamin supplements as your stomach may not be able to absorb as many nutrients as it was able to previously.

We at The Doctor Service strongly believe that most people should never require surgical intervention to manage obesity, and certainly not without significant long term lifestyle management first.


Obesity is a problem caused by negative lifestyle habits. In our modern urban environments, it can be easy to grow accustomed to these poor health choices and so it is important that we realise this and make the necessary changes to prevent them affecting our health.

Edited by Dr Kiran Sodha & The Doctor Service


  1. Sorensen TIA, Price RA, Stunkard AJ, Schulsinger F. Genetics of obesity in adult adoptees and their biological siblings. Br Med J 1989 1989;298(6666):87-90.
  2. Moore-Harrison T, Lightfoot JT. Driven to be inactive? The genetics of physical activity. Progress in molecular biology and translational science 2010 2010;94:271-290.
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