According to the Korean education ministry, which studied the physiques and exercise habits of almost 85,000 schoolchildren at 764 schools across the country last year, serious obesity has more than doubled since 2005, accounting for 1.6% of the students surveyed.
It found that sixth graders, ninth graders and seniors all gained weight compared to 10 years ago, and 15.6% of the subjects now weigh more than the average for their age group.
The average height of a sixth-grade boy is 151.4cm, 2.3 cm taller than a decade ago, and that of those in the ninth grade is 169.7 cm, 1.2 cm taller than 2005.
12th-grade boys have grown slightly shorter on average at 173.5 cm, compared to 173.6 cm in 2005. The average height of 12th grade girls is 160.9 cm, 0.1 cm shorter than in 2005.
Meanwhile, the number of youngsters who eat fast food increased among all age groups compared to 2014 and gets worse as they grow older.
The number who skip breakfast also increases as they get older, while the amount of vegetable and milk consumption falls.