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There has been an alarming rise in the number of obese people in the last few decades and the epidemic is turning into an unprecedented challenge for healthcare systems around the world.

However, apart from looking for ways to reduce weight or burn excessive fat, researchers have also been looking at the factors that contribute to obesity and the measures to prevent it. 

A debate on who gets fat and who does not has been reported by two experts in the British Medical Journal.

According to Timothy Frayling, Professor of Human Genetics at the University of Exeter, genetic factors are the main contributors to obesity in today's environment.

He says that previous studies conducted on twins and adopted children have suggested a strong influence of genetic component in the varying BMI, with an estimated 70% effect. Also, there are other studies that suggest that those carrying 2 copies of the obesity gene (the FTO gene) are heavier on average when compared to those carrying 2 copies of the protective version.

He added that another study conducted recently, involving  200,000 people, showed the strong effect of the FTO variant in sedentary people than in those who are physically active; however, studies of physical activity in schoolchildren suggest that education may not be as important as we think.

"Although DNA variations explain only a small percentage of the variation in body mass index, they provide proof of principle that genetic factors influence it over environmental factors," writes Frayling.

He concluded that genetic factors are major contributors to the BMI in a given population at a given time, and there is more and more evidence that these genetic factors may operate largely through appetite control.

"If true, plans based on changing our environment, such as banning the sale of supersized sugary drinks, may be more successful than plans to increase awareness through education," he adds.

On the other hand, John Wilding, Professor of Medicine at the University of Liverpool, blames environmental changes for increasing obesity.

Although he does acknowledge the role of genetics in the regulation of body weight, he argues that the sudden rise in the number of obese people in just last 30 years cannot be due to genetic changes. He adds that in the due course of time, there has been an overwhelming evidence that the environment has changed.

He points at the recent decrease in the prices of energy dense foods, growth and promotion of food industry, decline in physical activity due to changes in transport, technology and the built environment as key drivers for the obesity epidemic, Medical Xpress reported.

He says that although it's important to identify the genetic factors responsible for rare cases, but to deal with obesity as an epidemic, it is imperative to change the food and physical environment.

He calls for "a radical approach backed by strong legislation influencing food production and marketing, and ensuring the built environment and transport systems are designed to encourage active living."

"Obesity is a complex disorder with both genetic and environmental causes. The predominant driver is environmental, and changes to the environment will be essential if we are to tackle the current epidemic," he concluded.