The transition from adolescence to young adulthood is a particularly perilous one for our waistlines and our general health, as is made clear in two new systematic reviews published this week in the journal Obesity Reviews.
One review found that leaving high school is associated with a significant drop in physical activity, particularly for people who go off to college or university. The second review reports that becoming a parent is linked to a substantial gain of weight — for women.
“Children have a relatively protected environment, with healthy food and exercise encouraged within schools, but this evidence suggests that the pressures of university, employment and childcare drive changes in behaviour which are likely to be bad for long-term health,” said Eleanor Winpenny, the lead author of one of the studies and a behavioral epidemiologist at the University of Cambridge, in a released statement.
“This is a really important time when people are forming healthy or unhealthy habits that will continue through adult life,” she adds. “If we can pinpoint the factors in our adult lives which are driving unhealthy behaviours, we can then work to change them.”
For the first study, Winpenny and her colleagues conducted a meta-analysis of 19 previous studies that had examined how the transition from high school to college or a job affected people’s diet, physical activity and weight. The studies were all conducted in high-income countries (primarily in the United States and Australia), and most had been done within the past 20 years.
Seventeen of the studies looked specifically at changes in physical activity. When the data from those studies was pooled and analyzed, it showed that people decreased their moderate-to-vigorous physical activity by an average of seven minutes per day in the years immediately following high school. The drop was larger for men (16.4 minutes per day) than for women (6.7 minutes), and the biggest decrease was among young people who went off to college (11.4 minutes).
Those may seem like small amounts, but even a 6.7-minutes-per-day decline in physical activity adds up to 45 fewer minutes per week. Current physical activity guidelines recommend a minimum of 2.5 hours per week of moderate-intensity activity.
Winpenny and her colleagues found no further change in exercise habits after college, although people tended to get less physical activity once they started a job.
Two of the studies revealed that the quality of people’s diets tends to worsen (due primarily to a lower consumption of fruits and vegetables) after leaving high school — and again after leaving college.
Three studies showed an increase in body weight on leaving high school, but there wasn’t enough data to determine an average increase.
“The transition of leaving high school is an important time to support individuals to prevent decreases in physical activity and gains in body weight,” Winpenny and her colleagues conclude.
The second review looked at another transition during young adulthood — becoming a parent — and its impact on weight, diet and physical activity. Led by University of Cambridge epidemiologist Kirsten Corder, the review’s authors examined data from 11 previous studies from North America, Australia and Europe involving people aged 15 to 35.
The most striking finding came from the researchers’ meta-analysis of six of the studies — ones that followed women through young adulthood for an average of about five years. The change in body mass index (BMI) of the young women who became a parent during these studies was 17 percent higher than that of women who didn’t have children.
The researchers calculated that women of average height (5 feet 4 inches) in these studies gained an average of 16.5 pounds during five years, while women who became mothers gained an extra 2.8 pounds for an average total of 19.3 pounds.That was the equivalent of a 3.3 gain in BMI versus a 2.8 gain.
One study looked at how fatherhood affected men’s weight. It found no change.
The results regarding physical activity were less clear. Only two of the four studies that compared the exercise habits of new parents and non-parents reported that having a child led to a drop in physical activity. There was also only limited evidence of any kind of dietary differences between parents and non-parents.
Still, the weight gain observed in the meta-analysis among new moms is “alarming” and underscores “the need for obesity prevention for all young women, including mothers,” say the study’s authors.
“Interventions aimed at increasing parents’ activity levels and improving diet could have benefits all round,” says Corder in a released statement. “We need to take a look at the messages given to new parents by health practitioners as previous studies have suggested widespread confusion among new mothers about acceptable pregnancy-related weight gain.”
FMI: You’ll find both studies on the Obesity Reviews website.