A new study published in PLOS Genetics has found that people carrying genetic variants associated with obesity gain more weight today than individuals with the same genetic variants who were born before the onset of the modern obesity epidemic.

Researchers from University College London analyzed data from four British birth cohorts consisting of people born in 1946, 1958, 1970, and 2001. The study included body mass index (BMI) measurements collected from adolescence through adulthood, as well as information on several genetic variants previously linked to an increased risk of obesity.

The findings revealed an important pattern: the association between obesity-related genetic variants and higher BMI was weaker in earlier generations and became significantly stronger in more recent cohorts. The effect was particularly pronounced with increasing age and among individuals with higher BMI levels.

In other words, these genetic predispositions have always existed, but their influence appears to be stronger today than it was among people carrying the same DNA variants several decades ago.

The researchers attribute this change to shifts in the environment. Over recent decades, the availability of calorie-dense foods, processed products, and fast food has increased dramatically, while average levels of physical activity have declined. In this environment, genetic tendencies toward higher calorie consumption and weight gain may be expressed more strongly.

The authors stress that this does not mean the genes themselves have become “stronger.” Rather, the conditions in which those genes operate have changed. The same genetic profile can produce different outcomes depending on the surrounding environment.

The researchers note that this effect is especially evident among people with a high genetic predisposition to elevated BMI. These individuals appear to be the most responsive to changes in the food environment and lifestyle factors.

At the same time, the scientists emphasize that the precise mechanisms behind the amplified effect remain unclear. One hypothesis is that the modern food environment, characterized by widespread availability of ultra-processed foods, enhances behavioral and metabolic pathways linked to calorie intake.

The authors conclude that the modern obesity epidemic is neither solely a matter of genetics nor solely a consequence of lifestyle. Rather, it results from the interaction between the two: “the obesity epidemic increased BMI regardless of genotype, but those with the greatest genetic susceptibility were affected the most.”