People who carry genetic variations linked to obesity are more likely to be heavier now than individuals with the same variants who were born before the recent obesity epidemic, according to findings released on June 18. Liam Wright of University College London and colleagues reported these results in the journal PLOS Genetics.
Over the past five decades, obesity rates have risen sharply for both children and adults. Rates of extreme obesity have increased faster than overall increases in body mass index (BMI), which is an estimate of body fat based on a person's height and weight. This trend suggests that some individuals may be especially susceptible to environmental factors that encourage weight gain, such as greater availability of processed foods and lower levels of physical activity. One possible cause for this susceptibility is genetics.
To investigate this trend, researchers compared BMIs and the presence or absence of multiple genetic variations previously linked to obesity in people from four British birth cohorts born before or during the rise in obesity rates. The study included BMI data from early adolescence to adulthood for individuals born in 1946, 1958, 1970, and 2001 in Great Britain. Analyses showed that these genetic variations were more strongly linked with having a high BMI in the two more recent cohorts. The effect was even more pronounced as people became older and among those with higher BMI values. These findings suggest that people with a genetic predisposition to higher BMI are likely more susceptible than others to changes in their environment that encourage obesity.
The researchers said it remains unclear why there is a stronger association between genetics and BMI among younger cohorts, but suspect environmental changes—such as an increase in fast food restaurants and processed food—may enable greater expression of genetic variants associated with higher calorie consumption.
The authors concluded: "The obesity epidemic has increased BMI regardless of genotype, but it's those most genetically predisposed to high BMI that have been most affected." They said further work will be required to identify specific environmental factors responsible for strengthening the link between genetics and BMI.
