Obesity is a complex health condition influenced by genetics, lifestyle, metabolism, and the environment. Yes, genes can significantly influence a person’s susceptibility to obesity, but they do not determine body weight entirely. Understanding this relationship helps explain why some people gain weight more easily than others, even when their eating habits and physical activity levels appear similar.

How do genes influence body weight?
Genes provide instructions for making proteins that regulate different functions in the body. Several genes influence appetite, hunger, satiety (the feeling of fullness after eating), energy expenditure, fat storage, and the body’s response to food.
For example, some genetic variations may influence how strongly a person experiences hunger or how quickly they feel satisfied after eating. Other variations may affect how the brain responds to food-related signals or how the body regulates energy balance.
Research suggests that genetic factors account for approximately 40–70% of the variation in BMI between individuals in some populations. This is called heritability. Importantly, it does not mean that 40–70% of an individual’s obesity is caused by genes. Heritability describes differences across a population and can vary depending on the population and its environment.

Is obesity inherited from parents?
Genetic susceptibility can be inherited from one or both parents. A child whose parents have obesity may have a higher likelihood of developing obesity because they may inherit genetic variants associated with increased susceptibility.
However, children also share environmental influences with their parents, including dietary habits, physical activity patterns, sleep routines, and food availability. Therefore, a family history of obesity does not automatically mean that a child will develop the condition.

Can lifestyle overcome genetic susceptibility?
Genetic susceptibility does not mean that obesity is inevitable. Healthy dietary patterns, regular physical activity, sufficient sleep, behavioural support, and appropriate medical care can help improve health outcomes.
However, people respond differently to lifestyle interventions because of differences in appetite regulation, metabolism, medications, medical conditions, and other factors. Some individuals may require additional support, including specialist obesity care or medication.

Is obesity always caused by a single gene?
No. Most obesity is considered polygenic and multifactorial. Polygenic obesity results from the combined effects of many genetic variants, each usually contributing a small amount of risk. Multifactorial obesity develops through interactions between genetic susceptibility and environmental or behavioural factors.
A smaller proportion of cases are associated with a single-gene condition or a genetic syndrome. These may be suspected when severe obesity begins during infancy or early childhood, particularly when accompanied by intense hunger or other clinical features.

Why is genetic counselling important?
Genetic counselling helps individuals and families understand inherited susceptibility without unnecessary guilt or fear. A genetic counsellor can review family history, explain the difference between common genetic risk and rare genetic conditions, and discuss whether genetic testing is appropriate.