Comedian Kim Shin-young recently candidly shared her honest feelings about the yo-yo effect. On the May 5th broadcast of MBC FM4U's "Noon's Hope Song, Kim Shin-young," she said, "According to the solar terms, Gyeongchip has arrived, and my appetite is back," adding, "For me, Gyeongchip seems to have started around November." She continued, "Many people know this, but it has come back. Now I feel at ease. I have to eat everything I want."

Kim Shin-young appeared on JTBC's variety show "Knowing Bros" on April 28th and caused a big sensation by confessing to the yo-yo effect. She said, "I don't know why I gained weight. People say that if you lose weight and maintain it for about 10 years, no matter how much you eat, it won't return like before, but that's not true. It comes back immediately," adding, "There is no emotional change at all. I just thought I endured too much and decided to eat a little." She added, "I fell for chocolate cake. I eat seven packs of ramen. During my prime in 2003 when I used to eat 64 servings of thinly sliced pork belly, there was still a Shin-young left, which surprised me."

Comedian Hong Yoon-hwa, who is also experiencing the yo-yo effect alongside Kim Shin-young, is gaining attention. On May 3rd, she revealed on the YouTube channel "Nimam Naemam," "I lost a total of 40 kg after starting my diet, but now I have gained a little back." She explained, "It took nine months," and added, "At my peak, I was only the size of a compact car." Hong Yoon-hwa explained her reason for dieting, saying, "I'm still not slim, and many people ask, 'What exactly did you lose?' But at that time, I was really bigger than that tree, and I felt like if I gained that much weight, I would really die."

Kim Shin-young previously attracted attention for losing 44 kg. She revealed, "The doctor said that if I continued like this, I might not be here in 10 years," disclosing the health threats she faced. She said, "I am still maintaining abstinence from alcohol, but my weight has recently increased again. I don't know exactly why I gained weight," sharing the reality of the yo-yo effect. Kim Shin-young emphasized, "There is no special emotional change. I just thought I should live eating delicious food. I felt I had endured too much, so I started eating little by little."

The yo-yo effect is the phenomenon where weight increases again after weight loss, caused by the body's biological resistance to return to its original state for survival. When weight decreases, the leptin hormone that suppresses appetite decreases, and the ghrelin hormone that induces hunger increases. These changes are known to persist for more than a year after the end of a diet. According to research by a team led by Priya Sumisran, a professor at Melbourne Medical School in Australia, even one year after initial weight loss, the blood levels of appetite-related mediators that induce weight gain do not return to pre-weight loss levels.

Furthermore, when weight is lost through excessive dietary restriction called "extreme dieting," the body lowers the basal metabolic rate to conserve energy. At this time, if one eats as before dieting, the excess energy is stored as fat due to the lowered metabolism. Rapid short-term weight loss first breaks down muscle rather than fat to produce energy, and as muscle decreases, the ability to burn calories drops, turning the body into one that gains weight more easily.

Recent studies have also revealed that fat cells remember past obesity states, a phenomenon called "obesity memory," which causes the yo-yo effect. The research team explained that fat cells exposed to obesity change the way gene switches are turned on and off, remembering the past obese state. This genetic memory remains in fat cells for months to years even after weight loss and slimming, and these cells absorb and store fat much faster than normal cells when food is consumed again.

To reduce the yo-yo effect, lifestyle improvements such as increasing basal metabolic rate through strength training and increasing physical activity are necessary. Also, daily monitoring of weight and waist circumference, along with sufficient sleep and stress relief, are important to prevent false hunger triggers.

Kim Shin-young's confession about the yo-yo effect resonated with many. After the broadcast, comments poured in saying, "More like Kim Shin-young," with praise such as "She returned with style along with the weight," "Feels like the king's return," and "She came back as Kim Shin-young after gaining weight." On the show, Kim Shin-young said, "Hello, it's the returned Shin-young," showing a positive acceptance of her changes. These reactions reaffirmed Kim Shin-young's presence and charm.