Energy imbalances, some genetic or hormonal conditions, and certain medicines are known to cause overweight or obesity.^1b

The fundamental cause of obesity is an energy imbalance between calories consumed and calories used.^2a
Energy is measured in calories. When you take in more calories than you use, this creates an energy imbalance causing your body to store fat. This means your energy IN (food/drinks) does not equal your energy OUT (exercise).^1c,d

The body produces hormones that help maintain energy balances in the body. Conditions that affect these hormones can cause obesity.^1g These include:
Hypothyroidism. This condition is when a person has low levels of thyroid hormones. These low levels are associated with decreased metabolism and weight gain even when food intake is reduced. People with hypothyroidism also produce less body heat, have a lower body temperature and do not efficiently use stored fat for energy.^1h
Cushing’s syndrome. People with this condition have high levels of a hormone called cortisol. High cortisol levels make the body feel like it is under chronic stress. As a result, these people have an increase in appetite and the body stores more fat.¹ⁱ
Tumours. Some tumours near parts of the brain that control hunger can cause severe obesity.^1j

There are also medicines that can cause weight gain that leads to overweight and obesity, such as antipsychotics, antidepressants, antiepileptic drugs, and medicines used for diabetes.^1k
Talk to your doctor if you notice weight gain while you are using any one of these or other medicines. Do not stop taking the medicines without consulting your doctor first.^1k

Unhealthy lifestyle habits put people at higher risk of being overweight or obese. These include lack of physical activity, unhealthy eating patterns, not enough sleep and high amounts of stress.^1l
Unhealthy environments. Factors such as easy access to unhealthy fast foods, limited access to safe areas to exercise and play and exposure to chemicals can increase the risk for overweight and obesity.^1m
Age. The risk of unhealthy weight gain increases as you get older, however childhood obesity is also a serious problem.¹ⁿ
Race and Sex. Overweight and obesity can differ between race and between males and females. The body stores fat differently in men compared to women. Women tend to store less unhealthy fat in the stomach area than men do; and women with polycystic ovary syndrome (a condition that reduces fertility) are at greater risk for obesity.^1o,p
Genetics. Obesity can run in families – this means that genes associated with obesity/weight gain can be passed down in your DNA to your child. Eating too much or too little during pregnancy can affect how your child stores and uses fat later in life. Studies have also shown that obese fathers have DNA changes in their sperm that can be passed on to their children.^1q

Obesity may cause the following complications:^1v

• metabolic syndrome
• diabetes
• high cholesterol
• cardiovascular diseases (heart disease and stroke)
• breathing problems (sleep apnoea, asthma)
• back pain
• Osteoarthritis (a major cause of knee replacement surgery in patients who are obese for a long time)
• incontinence (weak bladder)
• low self-esteem or depression
• cancer

Treatment depends on the cause and how severe the condition is. Treatments include lifestyle changes, such as healthy eating and increased physical activity (exercise). There are also weight-loss medicines that can be prescribed, and surgery may be a treatment option.^1,4

Following a healthy eating plan with fewer calories taken in is usually the first step in trying to treat overweight and obesity.^4b When combined with healthy eating, regular physical activity will help you lose weight and stay at a healthy weight.^4c

Sugary drinks have no nutritional value. The average 500 ml fizzy drink contains around 10 spoons of sugar!^5b
Added sugar may be the unhealthiest ingredient in the modern diet^6a