Obesity is a state of excess body fat that presents a risk to one’s health.
Rather than measuring body fat directly to define obesity, the approach most frequently used is a measurement called Body Mass Index (BMI). BMI is calculated using measurements of your weight in kilograms and height in metres. It tells us whether a person’s weight is appropriate for their height. Depending on your BMI you may be classified as being underweight, healthy weight, overweight or obese (see table). A diagnosis of obesity is considered when the BMI is more than 30 Kg/m2. BMI is a helpful measurement because it predicts your risk of developing obesity related health problems. However, BMI has some limitations for instance it does not directly measure body fat and can inappropriately classify people who are very muscular as being overweight and obese.
Body Mass Index (BMI)
18.5 to 24.9 Kg/m2
25.0 to 29.9 Kg/m2
(Based on WHO classification)
Although BMI is the main tool used to define obesity it does not provide information about the location or distribution of excess fat on a person’s body. In some people, excess fat is evenly distributed around the body while in others they store most of their excess fat in the middle portion of their body (abdomen). Waist circumference (girth) is a very useful measurement that can describe fat distribution. This is important information because we know that storing excess fat in the middle portion of your body increases your risk of obesity related health problems when compared to storing it in other regions of the body.
In simple terms obesity develops when the number of calories (energy) we eat is greater than the number of calories that our body uses, when this happens the excess or unused energy is stored as fat. There are many factors that contribute to the imbalance between energy intake and energy output and it is usually a combination of these factors that lead to obesity. These include the following:
Genes - Research shows that obesity tends to run in families and studies with twins and adopted children have shown that genes play a key role in this. Genes can affect the amount and types of food that we prefer to eat, how much energy our bodies require and how fat is distributed around the body.
Environment - It is important to note that most of the increase in obesity rates has occurred over the last 50 years, during which time our genes have not changed significantly. This means that for most people, while their genes may drive their tendency to put on weight in a certain environment, it is the environment itself that has a greater influence, in particular changes in diet and activity levels.
Diet - The energy we put into our bodies is determined by the amounts and types of food that are available to eat. Portion sizes are getting bigger, usually at very little extra cost and there is increased use of convenient pre-packaged food, fast food and soft drinks, which are often high in calories.
Inactivity - In general, we are living more inactive lifestyles than we did in the past which means we burn fewer calories. The increased use of cars, changes in work practices and inactive pastimes, such as watching television and surfing the internet mean that people require fewer calories. Of course, an individual’s activity level can also be limited by factors that are beyond their control such and pain and other physical disabilities.
Medical problems - There are some infrequent medical causes for obesity, although these are uncommon. Some of these include glandular or hormonal problems (an underactive thyroid, known as hypothyroidism), reduced sex hormones (such as in the menopause), rare genetic causes (e.g. Prader-Willi syndrome) and some drugs (oral contraceptives, anti-psychotic drugs, anti-epileptics and steroids, and some diabetes medications).
The most obvious sign of obesity is when someone is carrying excess weight and has a BMI greater than 30 Kg/m2.
In the United Kingdom, the most recent estimates indicate that 29% of adults (~1 in 4) and 20% of children (~1 in 5) are obese. Obesity rates have increased significantly over recent decades, this increase is due to changes in our environment over that time. This in not just a problem in the UK and rates of obesity are high worldwide.
Differences in genes (DNA) between people can increase their risk of becoming obese. However, as previously mentioned, although genetic factors may drive an individual’s tendency to put on weight in a certain environment, it is the environment itself which has a greater influence. There are a number of rare cases of obesity that develop because of an abnormality in a specific gene, these individuals usually present as severe obesity that develops early in life.
There are many different strategies that are put forward to treat obesity and people can find it very difficult to lose weight. Losing weight is a long-term commitment and individuals need to find a strategy that works for them and that they can maintain over time. Before making any significant changes to lifestyle, it is advisable to visit the GP.
Obesity is treated in a number of different ways:
Many of the treatments for obesity involve having a healthy, balanced and active lifestyle, all of which impact positively on health
VLCD’s are generally well tolerated however, in addition to hunger, some people experience altered bowel habit, cramps and dizziness.
Orlistat may be associated with flatulence (wind) and abdominal discomfort. It may also change the consistency and frequency of bowel motions.
Bariatric surgery has a risk associated with it, between a 0.1% and 0.5% mortality rate, depending on the type of procedure undertaken. Patients are at risk of developing deficiencies in vitamin and minerals after the operation, these are usually prevented by monitoring and supplements, this is mostly seen with RYGB. In the case of sleeve gastrectomy patients may develop acid reflux after the surgery. Following either surgery, some patients can develop episodes of hypoglycaemia (low blood sugar) after meals or dumping syndrome which is the development of symptoms of nausea, sweating, diarrhoea or weakness after eating. All patients who undergo bariatric surgery require long-term follow-up.
Obesity is associated with a range of serious health problems, which have a negative impact on quality of life and life expectancy. These include conditions such as:
Metabolic and hormonal complications
Last reviewed: Jul 2019