• Genes - Research shows that obesity tends to run in families and genes (genetics) 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 need and how fat is stored around the body. There are also specific genetic conditions that can be inherited and increase the likelihood of weight gain and obesity, such as Prader-Willi syndrome.
• Environment - Most of the increase in obesity has happened in the last 50 years, which means that even though our genes haven't changed, our environment has. Today, we eat more high-calorie foods and are less active, which makes weight gain easier.
• Diet - The energy we get from food depends on the amounts and types of food we eat. Portion sizes are getting bigger, often for very little extra money, and there is increased use of convenient pre-packaged food, fast foods and soft drinks, which are often high in calories.
• Inactivity - In general, we are living more sedentary (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 reasons - There are some medical causes that could contribute to weight gain. These include problems with glands or hormones (like an underactive thyroid, known as hypothyroidism), lower sex hormones (such as during menopause). Certain medications can occasionally contribute to weight gain (such as anti-psychotic drugs, anti-epileptics and steroids).

How common is obesity?

Obesity is increasingly common worldwide and affects people of all ages. In the United Kingdom, a significant number of adults and children live with obesity, and this trend has been growing over recent years. This rise is seen in other parts of the world as well, partly because of changes in our lifestyles, including what we eat and how much we move.

Is obesity inherited?

Obesity can sometimes run in families, which means that some people might have genes that make them more likely to gain weight. However, the environment also plays a big role in whether someone becomes obese. Some people have genes that make it easier to gain weight, but lifestyle factors—like diet and physical activity—play a big part as well. Rarely, obesity may be caused by a specific genetic condition, especially if the weight gain starts very young and is more extreme.

Health problems connected to obesity

Obesity can cause serious health problems (referred to as obesity-related complications), which have a negative impact on quality of life and life expectancy (length of life).

Some of the main health issues connected to obesity include:

• Type 2 diabetes
• High cholesterol and blood pressure
• Heart disease and stroke
• Certain types of cancer
• Fatty liver
• Joint pain and movement issues
• Breathing problems during sleep (known as sleep apnoea)
• Fertility challenges
• Erectile dysfunction in men (problems with having an erection)
• Emotional challenges, like depression and social isolation

How is obesity managed?

Managing obesity can be challenging, and losing weight often requires long-term management. It's important to find an approach that fits well into daily life, and it can be helpful for a doctor, such as a General Practitioner (GP), to be involved.

Obesity is managed in a number of different ways:

• Dietary programmes – Eating fewer calories can help the body use stored fat for energy. In some cases, very low-calorie diets (VLCD) are recommended (calorie intake of 800 calories per day or fewer), but these should only be followed with a doctor’s supervision. VLCDs include the replacement of normal diet with meal substitutes. Such short-term interventions (usually around 12 weeks) are very effective at achieving weight loss and are followed by a food reintroduction phase.
• Exercise programmes – Exercise is vital to any weight management programme because it helps build muscle mass, increase metabolic activity and improve general health. Aerobic exercise (such as brisk walking or swimming) is of the greatest value for individuals who live with obesity. It is advised to aim for 30–60 minutes of continuous aerobic exercise several days a week. 
• Changing eating habits – Making gradual changes, like reducing snacks or focusing on healthier meals, can also help. Often, a health expert can provide support and guidance to make lasting changes.
• Medications –There exist several anti-obesity drugs available in the UK, which include Orlistat, Ozempic (Semaglutide) and Saxenda (Liraglutide). Orlistat is a capsule to be taken at mealtimes that blocks the action of enzymes (lipases) produced by an organ known as the pancreas. The role of these enzymes is to help the breakdown of fats in the gut, so that they can be absorbed. Therefore, Orlistat reduces the absorption of fat that comes from the diet (dietary). For the best results, it should be used alongside a healthy diet and regular exercise. Semaglutide and Liraglutide belong to a class of medications, known as Glucose Like Peptide-1 (GLP-1) agonists. These medications are usually given as an injection, either once daily or once weekly and they help in weight loss by making people feel fuller (satiated) and reducing appetite, which means less food intake overall.
• Surgery – For some people, surgery may be an option if other methods haven’t worked well. Weight-loss surgery, also called bariatric surgery, can be very effective for reducing weight and improving certain health problems related to obesity.

Common types of surgery are:

• Sleeve Gastrectomy: A large part of the stomach is removed, so the remaining stomach is smaller. This helps people feel full sooner and limits how much they can eat.
• Roux-en-Y Gastric Bypass (RYGB): This surgery makes the stomach smaller and bypasses part of the bowel (intestine). This means fewer calories are absorbed from food.

Surgery isn’t right for everyone, and a team of health professionals (known as multidisciplinary team, which consists of different experts, such as doctors specialising in obesity, surgeons, dieticians, psychologists) will help decide the best option. Bariatric surgery has also been shown to help reduce or even reverse health problems related to obesity, such as type 2 diabetes.