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.
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