Severe obesity is becoming more common around the world, and in many families several members live with excess weight. Society often puts obesity down to an unhealthy lifestyle, but the science tells a fuller story, because genes play a major part too. Poor diet and too little activity do contribute, yet they are not the whole picture. Obesity comes from a mix of biology and environment.
The inherited tendency to gain weight
Twin studies suggest that genes account for around 60% to 80% of the differences in body weight between people. Adopted children tend to resemble their biological parents in BMI far more than their adoptive families. Even identical twins raised in separate households end up with remarkably similar body weights, which shows just how strong the genetic influence is. Researchers now know that genes affect how full you feel, how your body handles and stores fat, how much energy you burn at rest, and even how strong your urge to move is.
How genes contribute to obesity
Family studies back this up, showing that a genetic predisposition raises the risk of obesity. For example, a child with two parents who have obesity faces a much higher risk of becoming overweight, even when they grow up with healthy eating and regular activity. Scientists have already identified many genetic variants linked to weight regulation. In a small number of children with severe obesity that starts very early, a fault in a single gene disrupts the brain’s hunger and fullness signals, which drives weight gain from a very young age.
Genes alone do not determine your future
A genetic predisposition does not make obesity inevitable. Genes may set the stage, but things like diet, physical activity, environment and daily habits have a strong say in whether someone actually develops severe obesity. In other words, genes explain the risk, but lifestyle shapes the outcome.
The balance between genetics and lifestyle
You cannot change your genes, but you can influence how they affect your health. Healthy eating, regular activity and lasting changes to your habits can all help offset a genetic tendency towards obesity. Your genes may make the journey harder, but they do not take away your ability to improve your health and manage your weight.
