Background: Data from the 1973-78 cohort of the ALSWH show that 60% of women who had a healthy weight at the start of the study in 1996 (age 18-23) maintained a healthy BMI over the subsequent 16 years, but that 40% transitioned to overweight or obesity. (Brown et al 2016). In 2013, a second cohort of 18-23 year olds was recruited (born 1989-95). Here we compare the rate of weight gain in the first four years of the 1989-95 cohort (2013-2017), with weight gain in the first four years of the 1973-78 cohort (1996-2000).
Methods: Data were from ALSWH participants who first completed surveys in 1996 or 2013, and again four years later (N= 16,066). All data were self-reported and high weight gain was defined as >2.5% per year.
Results: Average weight at baseline was almost 4kg heavier, the rate of weight gain was 1.7 times greater, and the prevalence of high weight gain (34.2% and 24%) was much higher, in the 1989-95 cohort than in the 1973-78 cohort. Factors associated with high weight gain in the 1989-95 cohort, but not in the 1973-78 cohort, included living in an outer regional area, having one child, being a former or current smoker, and high stress and depression. Based on average weight at age 21 and annual percentage weight gain, we estimate that women born in 1989-95 will, on average, be 16.7kg heavier at age 41 (93.2kg), than women in the 1973-78 cohort (76.5kg).
Conclusion: Without more effective weight gain prevention strategies we estimate that more than 50% of ‘millennial’ women will be in the obese BMI category in 20 years. This will have serious economic, health and societal consequences. More effective weight gain prevention initiatives are urgently required and should be targeted to those most at risk of high weight gain.