Genes play a significant role in determining a person’s weight and susceptibility to obesity, accounting for 40 to 70 percent of the variation in BMI within a population. According to obesity researcher Christoffer Clemmensen from the University of Copenhagen, many people are unaware of the substantial influence of genetics on weight.

A recent study published in Nature Medicine further explores this connection, with researchers developing an algorithm to predict a child’s likelihood of having a high BMI as an adult based on genetic data. Ruth Loos, the study’s lead author and professor of precision health at the University of Copenhagen, confirms the 40 to 70 percent estimate, noting slight variations across different studies.

While genetics have the strongest influence during youth, lifestyle factors become increasingly important with age. Genetics will account for a larger portion than otherwise, if everyone in a population has essentially the same lifestyle and eats the same diet.

Clemmensen highlights a societal difficulty in acknowledging the significant role of genetics in individual weight. He suggests this reluctance may stem from the close relationship people have with eating and the perception of control associated with food choices. However, he emphasizes that biological mechanisms can unconsciously drive individuals with increased genetic sensitivity towards behaviors like snacking on energy-rich foods.

The body has a potent biological defense against weight loss. Clemmensen points to the body’s strong biological defense against weight loss, making it exceptionally difficult to lose weight.

Research has identified over 1,000 gene variations associated with obesity, with the “FTO” gene having the most significant impact. Carrying a specific risk variant of the FTO gene can result in an average weight increase of 1.5 to 3 kilograms.

Despite these discoveries, a gap remains in understanding the full genetic contribution to weight, as known gene variants currently explain only 18 percent of the variation in BMI. Researchers believe there may be thousands of undiscovered gene variants with smaller individual effects that collectively contribute to weight.