Obesity does not just happen overnight - it develops gradually from poor diet and lifestyle choices and, to some extent, from your genes.
Lifestyle choices
Lifestyle choices are an important factor in influencing your weight. Eating more calories than you need may be down to poor food choices - for example, eating high fat, processed, or fast food - rather than filling up on fruit, vegetables and unrefined carbohydrates, such as wholemeal bread and brown rice. Alcohol also contains a lot of calories, and heavy drinkers are often overweight.
Bad eating habits also tend to run in families - rather than inheriting a slow metabolism, the habits learned from your parents can be an important factor. Childhood obesity is a strong indicator of weight-related health problems in later life, showing that learned unhealthy lifestyle choices continue into adulthood.
Lack of physical activity
Lack of physical activity is another important factor that is related to obesity. Many of us have jobs that involve sitting at a desk for most of the day, and we rely heavily on our cars to get around. When it is time to relax, we tend to watch TV, or play computer games, and rarely take any regular exercise. If we are not active enough to use up the energy provided by food, the extra calories are stored as fat instead.
Some people tend to stay the same weight for years without much effort, whereas others find they put on weight quickly if they are not careful. This could be due in part to your genes - scientists have discovered certain genes that make you feel hungrier, or make it take longer for you to feel full.
Medical reasons
In less than one out of every 100 cases, there is a medical reason for obesity. Conditions such as Cushing's syndrome (over-production of steroid hormones in the body) and an under-active thyroid gland are rare causes of weight gain.
Certain medicines, including some steroids and antidepressants, can contribute to weight gain. Also, taking the contraceptive pill and quitting smoking may increase your appetite.
