General economic factors, ranging from unemployment to income, as well as the monetary or time costs of eating and physical activity account for 43 percent of the rise in obesity, according to a recent study published by the U.S. National Bureau of Economic Research, as the adult obesity rate in the United States has surged from 13 percent in 1960 to 35 percent in 2012.

　　"Supercenter/warehouse club expansion and increasing numbers of restaurants are the leading drivers of the results," the study concluded. "We show that supercenter/warehouse club density increases the probability of weight loss attempts, raising the possibility that cheap food from these retailers triggers self- control problems."

　　Study links growing obesity in Americans to big-box stores, restaurants

　　The study suggests that the rise of supercenters and warehouse clubs, like Walmart and Costco, may impact Americans' eating habits as they make calorie-rich food cheaper and more accessible, and save customers a lot of time.

　　"Food's gotten cheaper and more readily available, so we eat more of it. It's really simple," said Charles Courtemanche, co- author of the study and a health economist at Georgia State University, in an interview with National Public Radio (NPR). "At least a sizable portion of the rise in obesity can be characterized as response to economic incentives."

　　Obesity, defined as a body mass index (BMI) of at least 30, leads to adverse health conditions such as heart disease, diabetes, high blood pressures and stroke.

　　Obesity has become a major public health concern in the United States as the nation has one of the highest obesity rates in the world, according to the Organization for Economic Cooperation and Development (OECD).