Why am I overweight?

Why one person should be more overweight than another is a commonly asked question.

Unfortunately there is no easy answer. At its simplest level, obesity occurs when we take in more energy (in the form of calories) than we are expending, (by being active). Adding as little as an extra 50 calories more than recommended every day – about half a biscuit – and gaining just one to two extra kilos every year over ten years, could be enough to move you from a healthy weight range, to an overweight or obese one.

  • Many things may contribute to you being overweight.
  • More commonly, weight gain is due to the environment we live in and genes that influence our behaviour in that environment.
  • Rarely, some medical conditions such as hypothyroidism, Prada Willi syndrome, Cushing's syndrome or polycystic ovary syndrome (which can cause an imbalance of hormones) can contribute to weight gain.
  • Certain medications may also lead to weight gain.

The environment

We are all surrounded by tempting calorie dense foods, and we rely more on convenience foods. There are many labour saving devices, and we also spend more time watching television, which reduces opportunities for being active.


Genes account for 70% of why a person becomes overweight or obese, whilst our environment accounts for 30%.

We don't know the exact role that our genes have to play in obesity. It has been suggested that they may work by making some people less able to tell when they have eaten enough food or by making some people more responsive to the sight and smell of food and so eat more than they need to.

As we inherit our genes from our parents, this partly explains why weight gain is more common in some families than others.

The impact of genes means that if you are overweight or obese you may have to work harder to control the types and amounts of food that you are eating, in order to manage your weight.