The team from the University of North Carolina at Chapel Hill found genetic sites that affect human body’s size and shape, including height and obesity. The findings will help understand how genes can predispose certain individuals to obesity.

In the study, published in the journal Nature Genetics, researchers found 24 coding loci (or positions) — 15 common and nine rare — along chromosomes of individuals that predispose to higher waist-to-hip ratio.

Higher values of waist-to-hip ratio are associated with more incidence of diseases associated with obesity.

“For the first time, we were able to examine, on a large scale, how low-frequency and rare variants influence body fat distribution,” said North.

“A better understanding of the genetic underpinnings of body fat distribution may lead to better treatments for obesity and other downstream diseases obesity also impacts, for example Type-2 diabetes and heart disease,” suggested North.

Further analysis revealed pathways and gene sets that influenced not only metabolism but also regulation of body fat tissue, bone growth and adiponectin, a hormone that controls glucose levels and breaks down fat.

Performing functional studies across other organisms, the team also identified two genes that were associated with significant increase in triglyceride and body fat across species.

The research, published in the International Journal of Epidemiology, showed that the psychological impact of being overweight causes depression, rather than associated illnesses such as diabetes.

“Our research shows that being overweight doesn’t just increase the risks of chronic diseases such as cancer and cardiovascular disease; it can also lead to depression,” said study co-author Elina Hypponen, Professor at the University of South Australia.

For the study, the researchers looked at UK Biobank data from more than 48,000 people with depression, comparing them with a control group of more than 290,000 people born between 1938 and 1971, who provided medical and genetic information.

Hospital data and self-reporting were used to determine whether people had depression.

The team used a genetic research approach to explore the causal link between the two conditions.

They separated out the psychological component of obesity from the impact of obesity-related health problems, using genes associated with higher BMI but lower risk of diseases like diabetes.

“These genes were just as strongly associated with depression as those genes associated with higher BMI and diabetes. This suggests that being overweight causes depression both with and without related health issues – particularly in women,” Hypponen said.

“Our robust genetic analysis concludes that the psychological impact of being obese is likely to cause depression. This is important to help target efforts to reduce depression, which makes it much harder for people to adopt healthy lifestyle habits,” said Jess Tyrrell of the University of Exeter Medical School in Britain.