What’s Her Secret?

Kim (35, female) retained her youthful figure well up until her mid-20s.

After marriage and her first pregnancy, her 20 kilograms of added weight still has seven more post-birth kilograms to go. After her second child, she gained three kilograms, and for some unknown reason, she gains about a kilogram every year.

Whenever she sees her high school friend Lee, she gets bitter. They’re both mothers to two children, but Lee has remained more or less the same as her pre-marriage years. Kim wonders, “She doesn’t exercise, so what’s her secret?”

Yoon Geon-ho from the Catholic University of Korea College of Medicine says, “This kind of disparity occurs because there was a difference in so-called body ‘quality’ in their teenage or pre-teen years. It’s not only the outward health that matters, but the ‘body quality’ that is accumulated over a lifetime.”

Yoon’s research team conducted body mass index (BMI) and hormone research on 451 high school students in Seoul and Jeju and say that “city girls are more likely to become rapidly obese in their adult years compared to country girls. They may be the same weight, but their muscle and fat ratios are radically different.”

According to the research, the average BMI of urban and suburban girls was 21.3 and 21.8 respectively, showing no great difference. In fact, overweight girls with BMIs of over 25 accounted for nearly 13 percent in suburban areas, as opposed to the 5.0 percent in cities. But the hormone that increases with body fat was much higher for the city students than the country students. This means that although the outward appearance of two physically fit students may be the same, the urban student may have less muscle mass and more body fat.

Yoon says, “It’s because urban girls exercise less and eat a lot of fast food. If muscle mass is smaller, than the metabolism is lower, so loosening up on your daily regimen will take a heavier toll.”

For male students in the urban areas, their “body quality” was lower than the country boys in all aspects. Their average body mass of 23.8 was significantly higher than the 21.3 of suburban students, and obese students with BMIs of over 25 were 31 percent for city boys and 6.6 percent for country boys. Their fat hormones were also higher.

Yoon warns, “The students in the city had higher blood sugar and cholesterol levels. They may be normal in their teenage years, but 10 years later, the obesity and body fat will catch up to them through diabetes and coronary heart disease.”

Na-Yeon Lee larosa@donga.com