Several studies released on Tuesday show women are most vulnerable to putting on pounds at puberty, after pregnancy and after menopause, giving doctors new information to help reduce obesity among females.

The prevalence of obesity in North American women has almost doubled in the last 20 years, and while many factors were cited in presentations at a conference on obesity in Long Beach, Calif., south of Los Angeles, a lot of research showed women putting on the most weight during those three life-changing periods.

"It could easily be the number of times you go for Happy Meals," one researcher said, citing similar patterns of weight gain for new fathers as well as mothers. "But there may be a physiological component for women."

Experts at the annual meeting of the North American Association for the Study of Obesity in Long Beach, Calif. said identifying key stages and causes of weight gain is critical for developing prevention programmes to stop or slow the trend.

"We are trying to look across hormonal transitions in a woman's life. All three of these stages are associated with changes in fat deposition and distribution," said Aviva Must, associate professor of the Department of Family Medicine and Community Health at Tufts University School of Medicine in Boston and the lead investigator on the puberty studies.

Must presented results from two studies suggesting that early menarche (the onset of menstrual cycling) in young girls sets the stage for obesity later in life.

"It has long been known that kids who are overweight will mature earlier than their age-matched peers. There is an epidemic of childhood obesity and puberty has been identified as a potentially critical period in the development of obesity," Must said.

She added that if early menarche were established as a critical risk period, obesity prevention and treatment strategies, such as more exercise, could be better targeted.

Must said data from the Tufts studies indicates some impact from early menarche on obesity later in life, but the strongest correlation is between childhood obesity and weight gain as an adult.

Other data presented by researchers from the University of Alabama at Birmingham showed that weight retention following pregnancy may be a factor in the obesity of young women.

They found that while most women experience a modest weight gain after pregnancy, obese women are at risk for substantial weight gain. In addition, they found that African American women are at greater risk than Caucasian women.

"Weight gain after pregnancy may reflect changes in lifestyle behaviours rather than physiological changes associated with giving birth. My guess is it's a little bit of both," said Delia Smith West, associate professor of Medicine at the Alabama university.

The five-year observational study found that women who had given birth gained an average of around 20 pounds (9 kg), compared with an average of 11 pounds (5 kg) for childless women.

"Obesity prevention programmes that focus on changes in diet and physical activity patterns offer promise for reducing weight retention after pregnancy. We don't want women dieting the entire time they are pregnant," West said.

Weight gain during menopause may also be significantly prevented by long-term changes in dietary intake and increased physical activity, according to findings of the Women's Healthy Lifestyle Project, a five-year, randomized clinical trial, funded by the National Institutes of Health.

"Weight change in the older woman may be more strongly associated with ageing than with menopause. However, post-menopausal women have higher levels of body fat and central adiposity than other women the same age," study presenter Laurey Simkin-Silverman, assistant professor of Epidemiology and Psychiatry and Health Services Administration at the University of Pittsburgh, said in a statement.

The Women's Healthy Lifestyle Project studied 535 pre-menopausal women who were randomly assigned either to a group that was given a low-fat, reduced-calorie diet and physical activity, or to an assessment-only control group.

Four and a half years into the study, twice as many women in the intervention group were at or slightly below their original weight compared with the control group, which had progressively gained weight (an average of 5.2 pounds (2.4 kg) over the course of the study.

Overall, the study demonstrated that both physical activity and reducing saturated fat in the diet are key to preventing weight gain, the researchers said.

(From China Daily)