Obesity is caused by a combination of genetics and lifestyle factors,
and therefore diet and exercise alone are not always sufficient for
weight loss3. The cause and management of obesity is still
greatly misunderstood, causing people living with obesity to feel as
though they are to blame, and they continue to face stigma, bias and
discrimination, all of which can have a significant impact on their
Obesity is a complex disease that can be caused by multiple factors.
Up to 70% of weight health can be linked to genetics and it can also
be influenced by physiological, psychological, environmental and
Our weight changes when energy intake is not equal to energy
expenditure. This is referred to as our ‘energy balance’, and is
influenced by many factors, some of which are outside of our control.
Biology: Up to 70% of the causes of obesity can be linked to
genetics, family history and ethnicity6. In some cases,
genetics can increase the risk of a person developing obesity by
20–30%6. Some medical conditions can cause people to gain
weight – for example, conditions affecting the endocrine system can
cause hormone imbalances that affect a person’s energy balance7.
Psychological wellbeing: some people eat more when they are
tired, angry8 or stressed7, or as a result of
some common medications, e.g. antidepressants7
As a result, it’s not surprising that two people who exercise and
eat equal amounts, will likely have different body shapes, and won’t
lose weight at the same momentum. Identical twins could have entirely
different eating habits and levels of exercise, but ultimately similar
body weights due to their near-matching genetic make-up.