Final answer:
Weight gain during adolescence is considered normal and part of healthy development, although the rising trend in obesity among teenagers is a separate concern that poses health risks.
Step-by-step explanation:
Weight gain during adolescence is expected and healthful: True. During the adolescent years, the body goes through numerous physical changes, including increases in height, muscle mass, bone density, and body fat, particularly for girls. This growth in weight is a natural part of development, especially when considering that in boys the age at greatest speed (AGS) in weight lags behind the AGS in height by about three months, and in girls by about six months. Nevertheless, it's important to differentiate between healthy development and the distressing trend of obesity, which is characterized by having a body weight at least 20 percent higher than what is considered healthy for a certain height. The rate of obesity in teenagers has indeed tripled since 1980, causing concerns over potential health issues such as type 2 diabetes and heart disease, conditions linked with excessive weight gain.