According to a new study the increase in desk jobs for the last 50 years may be the major cause for the risen obesity rate in United States.

Contemporary workers burn around 120 to 140 fewer calories per day at their job than workers in 1960s.

The study revealed less than 20% of jobs involve even moderate physical activity, compared to over 40% of jobs in the 1960s.

Men burn an average 142 less calories a day at work; women, 124.

The decrease in activity level is due to a significant plunge in the number of active jobs in manufacturing and farming and a boost in office jobs that are mostly sedentary.

The jobs requiring moderate physical activity have all but disappeared, says Timothy Church, the study's author and a director of preventive medicine research at the Pennington Biomedical Research Center in Baton Rouge.

Around one third of adults in the USA are obese, defined as 30 or more pounds over a normal weight. That is approximately 13% higher than in the early 1960s.

The author says this change in the work environment doesn't wholly explain the reason for rise in obesity, however, he believes that it has influenced the obesity rate in this country.

Barbara Rolls, professor of nutritional sciences at Pennsylvania State University, says obesity epidemic is not due to work environment change alone, but so many people are overeating a lot.

The recent study has also revealed the sedentary time has been closely linked to higher death rates.

In addition to the decrease in physical activity in the workplace, the study remarked that diet, lifestyle, and genetics may also play a major role in obesity.

Statistics show that around 30 percent of Americans are obese (BMI of 30 or above) and that the related cost of that obesity hit $270 billion. 

The study's findings appear online in PLoS (Public Library of Science) ONE.