It was a provocative（刺激的，挑拨的） prediction that due to the obesity epidemic Baby Boomers（婴儿潮一代） may outlive（比……活得长） their children. But a new study by the University of Michigan Health System on obesity trends shows Americans are getting heavier younger and carrying the extra weight for longer periods over their lifetime.

As a result, the study suggests the impact on chronic diseases and life expectancy（期望，期待） may be worse than previously thought. The findings will be published April 12 in the International Journal of Obesity.

In the Journal, researchers report that 20 percent of those born 1966-1985 were obese by ages 20-29. Among their parents, those born 1946-1955, that level of obesity was not reached until ages 30-39, not until ages 40-49 for individuals born between1936-1945, and obesity prevalence was even later – during the 50's – for those born between 1926-1935.

Further research is needed to understand the future effect the obesity trend will have on diabetes（糖尿病） rates and mortality.

"Many people have heard that Americans are getting heavier," says lead author Joyce Lee, M.D., M.P.H., a pediatric（小儿科的） endocrinologist（内分泌学家） at the U-M Mott Children's Hospital and assistant professor in the Department of Pediatrics and Communicable Diseases at the U-M Medical School. "But it's very important to understand who the obesity epidemic is affecting.

"Our research indicates that higher numbers of young and middle-age American adults are becoming obese at younger and younger ages," she says.

Evidence shows body mass index（身体质量指数） , a calculation of fat and weight, increases with age, and children who are obese are more likely to become obese adults.

The prediction, made in 2005, for a reduced life expectancy（平均寿命，预期寿命） in the 21st century, was based on obesity prevalence from the period 1988-1994, the mid-point of the obesity epidemic, and included much older adults, born 1885-1976, a generation that had much lower obesity rates over their lifetime.

Obesity is a well-known contributor to type 2 diabetes（糖尿病） , cardiovascular disease（心血管疾病） , disability and premature death（过早死亡） .

The federally funded U-M study shows obesity trends were worse for women and blacks, a bad sign for reversing racial disparities（不等，不同） in health, U-M authors say. Among 20-29-year-olds, born 1976-1985, 20 percent of whites were obese compared to 35 percent of blacks in that age group.

"What is particularly worrisome（令人烦恼的，麻烦的） is that obesity trends are worse for blacks compared to whites," Lee says. "Black Americans already experience a higher burden of obesity-related diseases and the obesity trends will likely magnify（放大，赞美） those racial disparities in health."