Fat around the tummy is known to increase the risk of several chronic health complications. A new study has found that the United States is now fighting a battle of bulge, with waistlines registering significant expansion in the past few years.

The study, conducted by researchers at the U.S. Centers for Disease Control and Prevention, Atlanta, states that average waistline for people living in the U.S. increased by 1in (2.5cm) between 1999 and 2012, BBC reported.

CDC states that another measure for obesity - the body mass index - remained more or less same during the same period. The study shows that the current standard of defining obesity might not be enough and clinicians need to account for belly fat.

Past research has shown that abdominal fat is the most dangerous type of fat out there and that it is associated with an increased risk of heart problems as well as a shorter lifespan.

Data for the study came from the National Health and Nutrition Examination Survey (NHANES). More than 32,816 men and non-pregnant women participated in the study. The researchers obtained information about participants' age and waist circumference.

In the study, abdominal obesity was defined as waist circumference greater than 34.6 inches (88 cm) in women and 40.2 inches (102 cm) in men.

The team found that waist circumference increased in both genders as well as in different ethnicities. Overall waist size expanded from 37.6 inches in 1999-2000 to 38.8 inches in 2011-2012. During this period, men's waist circumference increased by 0.8 inches, women's by 1.5 inch, non-Hispanic whites (1.2 inch), non­Hispanic blacks (1.6 inch). The greatest increase was seen in Mexican Americans whose waist grew by 1.8 inch, according to a news release.

Previous analysis of the same NHANES data had shown no significant increase in obesity. "In contrast, our analyses using data from the same surveys indicate that the prevalence of abdominal obesity is still increasing. The reasons for increases in waist circumference in excess of what would be expected from changes in BMI remain speculative, but several factors, including sleep deprivation, endocrine disruptors, and certain medications, have been proposed as potential explanations," the authors said in a news release.

"Our results support the routine measurement of waist circumference in clinical care consistent with current recommendations as a key step in initiating the prevention, control, and management of obesity among patients," they added.

The study is published in the Journal of the American Medical Association.

City University London scientists had recently said that maintaining a waist size that is less than half of the height can help increase lifespan.