The nation's obesity prevalence increased from 13 percent to 32 percent between the 1960s and 2004, said researchers from the Johns Hopkins Bloomberg School of Public Health Center for Human Nutrition.
"The obesity rate in the United States has increased at an alarming rate over the past three decades. We set out to estimate the average annual increase in prevalence as well as the variation between population groups to predict the future situation regarding obesity and overweight among US adults and children," said Youfa Wang, lead author of the study.
"Obesity is a public health crisis. If the rate of obesity and overweight continues at this pace, by 2015, 75 percent of adults and nearly 24 percent of US children and adolescents will be overweight or obese."
According to the meta-analysis, which included a review of 20 journal papers, reports and online data, the prevalence of obesity and overweight has increased at an average rate of 0.3-0.8 percentage points across different socio-demographic groups over the past three decades.
Some minority and low socioeconomic status groups are disproportionately affected by obesity, said the researchers. Such groups include non-Hispanic black women and children, Mexican-American women and children, low socioeconomic status black men and white women and children, Native Americans and Pacific Islanders.
In order to examine the disparities in obesity, the researchers used data from four national surveys - NHANES, BRFSS, Youth Risk Behavior Surveillance System and National Longitudinal Survey of Adolescent.
The meta-analysis, which was published online in May, in advance of the 2007 issue of the journal Epidemiologic Reviews, found that 66 percent of adults were overweight or obese in 2003-2004. Some 16 percent of children and adolescents were overweight and 34 percent were at risk of becoming overweight in 2003-2004.
The study defined adult overweight and obesity using body mass index cutoffs of 25 and 30, respectively. The researchers said it is inaccurate to use the term 'obese' when referring to children and adolescents because the Centers for Disease Control and Prevention uses 'overweight' to refer to the highest body mass index for children and adolescents. As a result, the study classifies children at risk for overweight as being in the 85th and 95th percentiles of body mass index.
The study also found that women 20-34 years old had the fastest increase rate of obesity and overweight. White children and adolescents had the lowest prevalence of overweight and being at risk of overweight compared with their black and Mexican counterparts.
Some 80 percent of black women aged 40 years or over are overweight, while 50 percent are obese, said the study. Asians were found to have lower obesity prevalence when compared to other ethnic groups. However, Asians born in the United States are four times more likely to be obese than their foreign-born counterparts.
In addition, the study noted that less educated people have a higher prevalence of obesity than their counterparts, with the exception of black women. States in the southeast have higher prevalence than states on the West Coast, the Midwest and the Northeast.
"Our analysis showed patterns of obesity or overweight for various groups of Americans. All groups consistently increased in obesity or overweight prevalence, but the increase varied by group, making this public health issue complex. More research needs to be completed to look into the underlying causes," said May Beydoun, coauthor of the study.
"Obesity is likely to continue to increase, and if nothing is done, it will soon become the leading preventable cause of death in the United States."
