Dropping out of school and finding a job have both led to a decrease in physical activity, while becoming a mother has been linked to increased weight gain, conclude two reviews led by researchers at the University of Cambridge.
Many people tend to gain weight as they exit adolescence and into adulthood, and this is the age when obesity levels increase most rapidly. This weight gain is related to changes in diet and physical activity during the life events of early adulthood, including transition from school to secondary education and work, entering into new relationships and having children.
Researchers from the Center for Diet and Activity Research (CEDAR) in Cambridge wrote in Obesity Reviews about changes in exercise, diet and body weight as young adults move from education to work and age. To do this, they conducted systematic reviews and meta-analysis of existing scientific literature – these approaches allow them to compare and consolidate the results of a number of often conflicting studies to arrive at more robust conclusions.
Leave school
In the first of the two studies, the team looked at the evidence related to the transition from high school to higher education or employment and how it affects body weight, diet and physical activity. In total, they found 19 studies of 15-35 years of age, 17 of which evaluated changes in physical activity, three body weight and five dieting or eating behaviors.
The team found that dropping out of high school was associated with a seven-minute reduction per day of moderate-to-vigorous physical activity. The decrease was greater for men than for women (a decrease of 16.4 minutes per day for men compared to 6.7 minutes per day for women). More detailed analysis showed that the change is greatest when people enter university, with an overall rate of moderate to vigorous physical activity at 11.4 minutes per day.
Three studies reported body weight gains upon high school leaving, although there weren't enough studies to indicate average weight gain. Two studies suggested that diets deteriorate in quality upon high school leaving and one suggested the same upon leaving university.
Getting older
In the second study, the team looked at the impact of aging on weight, diet and physical activity. A meta-analysis of six studies found that the difference in body mass index (BMI) change between childless and aging was 17%:an average height woman (164 cm) who had no children came to about 7.5 kg in five to five six years, while a mother of the same height would gain an additional 1.3 kg. These correspond to an increase in BMI of 2.8 versus 3.3.
Only one study looked at the impact of fathering and found no difference in change.
There was little evidence of physical activity and diet. Most studies, including physical activity, showed greater parental decline than non-parents. The team found limited evidence for diet, which did not appear to differ between parents and non-parents.
“BMI rises for women above young adulthood, especially among mothers. However, new parents may also be particularly willing to change their behavior, as it can positively impact their children as well, rather than just improve their own health," said Dr. Kirsten Corder, also from CEDAR and the MRC Epidemiology Unit.
