Changes in Weight Throughout the Life Span


In Childhood


BMI is used to determine weight status among children just as it is in adults. However, in children and adolescents, BMI cutoff points defining obesity are age-specific and sex-specific in a manner that is typically referred to as BMI-for- age.31


The CDC growth charts are commonly used to categorize children’s and


adolescents’ weight-for-age status into corresponding percentiles. Obesity in chil- dren and adolescents is defined as a BMI at the 95th percentile or greater. Weight- for-height tends to increase in late childhood before puberty. It then falls during puberty, as linear growth accelerates. Weight then rises again in late adolescence and the period of emerging adulthood. Using BMI-for-age criteria, obesity prev- alence rises with increasing age. Data from 2017–2018 show that the prevalence of obesity was 13.4% among 2- to 5-year-olds, 20.3% among 6- to 11-year-olds, and 21.2% among 12- to 19-year-olds. As is true for adults, the prevalence of obe- sity is higher among Hispanic children (25.6%) and non-Hispanic Black children (25.2%), as compared to non-Hispanic White children (16.1%) or non-Hispanic Asian children (8.7%).29


In Emerging Adulthood


Recent analyses have focused on the period of life from age 18 years to 25 years as a life stage for which obesity prevalence has been growing. This period, referred to as emerging adulthood, is characterized developmentally as a time of life when indi- viduals transition from school to work and develop lifelong lifestyle habits along with an adult identity. An analysis of NHANES data showed that, between 1976 and 2018, the average BMI among emerging adults increased from 23.1 to 27.7. The prevalence of obesity in this group increased from 6.2% in 1976–1982 to 32.7% in 2017–2018. In contrast, the prevalence of normal weight in this group decreased from 68.7% to 37.5% over the same time. A particularly sharp rise in the prevalence of obesity occurred between 2016 and 2018.32


Future studies should focus on the establishment of lifelong lifestyle habits in this group of young adults.


During Pregnancy Weight gain during pregnancy is normal and important for the development of the fetus. However, excessive weight gain can lead to adverse consequences for both birth parent and child that may extend beyond pregnancy. Individuals gain an average of 14.1 kg (31 lb) during pregnancy, although those with obesity gain less weight—those with class 1 obesity gain an average of 12.2 kg (27 lb); those with class 2 obesity, 10.3 kg (23 lb); and those with class 3 obesity, 8.2 kg (18 lb).33 In 2009, the National Academy of Medicine issued guidance on the appropriate degree of gestational weight gain. These recommendations were based on the risk of adverse health consequences to the baby and birth parent associated with exces- sive gestational weight gain. These guidelines suggested a range of appropriate ges- tational weight gain of 5 to 9 kg (11 to 20 lb) for individuals with obesity.34


In 2019,


the LifeCycle Project–Maternal Obesity and Childhood Outcomes Study Group conducted a meta-analysis of the relationship between gestational weight gain and infant and birth parent outcomes in people with obesity. They suggested that the appropriate level of gestational weight gain in those with class 1 obesity was 2 to 6 kg (4 to 13 lb); in those with class 2 obesity, it was less than 4 kg (9 lb); and in those with class 3 obesity, less than 6 kg (13 lb).35


A more recent retrospective 18 SECTION 1: Foundations of Treatment: The Human Element


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