THURSDAY, July 21 , 2011 (HealthDay News) -- The epidemic of excess weight gain and obesity among young Americans began about 15 years ago, a new study finds.
"Our research documents the emergence of the obesity epidemic among adolescents in the later half of the 1990s, and among young adults in 2000," said Hedwig Lee, who led the study while at the University of North Carolina at Chapel Hill. She is now an assistant professor of sociology at the University of Washington in Seattle.
"The jury is still out about all the possible causes for the increasing weight gain among adolescents . . . as well as for the entire population," said Lee.
However, she cited a number of possible factors, including a rise in time spent in front of computer or TV screens and longer time spent in post-secondary education, "transitioning" to adulthood. According to Lee, poor diet and couch-potato lifestyles rise when young people leave the parental home and go out on their own, before starting their own families.
The research focused on a measure called the body mass index, or BMI, which calculates a relationship between weight and height.
As BMI grows, so do concerns arise about obesity-related illnesses, including heart disease, diabetes, some cancers, stroke, liver disease, gall bladder disease, osteoarthritis and fertility problems, Lee said.
According to the U.S. Centers for Disease Control and Prevention, about one-third of Americans are now either overweight or obese, with slightly more women than men affected.
The study of about 100,000 adolescents and young adults used four large national databases tracking the BMIs of 12- to 26-year-olds from 1959 to 2002.
The results showed that BMIs increased "sharply in the adolescent ages beginning in the 1990s, and among young adults around 2000," especially among black females. Overall, BMI increases started earlier and rose faster for females versus males, according to the study, which was published online this month in the Journal of Adolescent Health.
BMI scores of 18.5 to 24.9 fall within a "healthy range," while those between 25 to 29.9 are classified as overweight. A BMI of 30 or more is considered obese.
According to the study, the BMI of the average 18-year-old from 1959 to 1980 stayed relatively stable at 22. However, it had risen to 23 by 1990, and to about 25 by 2000, the researchers found. That would translate into a weight gain from an average of 149 pounds to an average of 166 pounds for a 5-foot 9-inch, 18-year-old male. An average 5-foot 5-inch female's weight increased from 132 to 147 pounds.
Trends were shown only for blacks and whites because racial categories for other ethnic groups were not part of all the data sets. Data for these groups were included as part of the total picture.
According to one expert on nutrition and weight, the study documents how a problem that used to begin in middle-age is now affecting young adults.
"It used to be middle-age creep," said Lona Sandon, assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center. "It's scary because the earlier weight gains mean earlier onset of chronic illness such as hypertension (or high blood pressure) in the 20s instead of 40s."
While it is unclear why black girls, especially, began gaining more weight more quickly, Sandon noted that black female adults are also heavier, on average, than other women. Poor access to health care may be a bigger issue for black women, she said.
"If you don't have access to health care, you're not going to focus on your health," she said.
Intervention is important before weight gain become entrenched, Sandon stressed. She believes that educational efforts need to focus on younger children. Schools also can change the types of food and drinks they serve, she added.
For adults, workplaces need to become "exercise friendly" because that's where adults spend most of their time, Sandon explained. "We need to remove the barriers" that keep people from exercising and eating healthy foods, she said.
To learn more about teens and weight trends, visit the U.S. Centers for Disease Control and Prevention.