Actress Koo Hye-sun, 41, revealed that she recently gained 8 kg back following an intense weight loss journey.
Writing on social media on the 16th, Koo shared, "After returning from the Himalayas, I went on air having gained 8 kg, and I feel sorry for looking chubby on MBN's Kim Ju-ha's Day & Night."
On the program, Koo explained what initially prompted her diet: "In 24 years of working in broadcasting, I received my first malicious comment calling me a 'pig.' The moment I saw that comment, I stopped eating—I cut out solid food entirely." In March, Koo had announced that her weight dropped from 60 kg to 46 kg.
However, the weight quickly returned following an extreme physical challenge. Koo recently completed a trek in the Himalayas, achieving her goal of reaching an altitude of 4,300 meters. "It was a forced march—walking 16 hours a day," she explained.
Yet despite the grueling effort, she gained 8 kg during the expedition. Explaining the rebound, Koo admitted, "You can't keep going if you don't eat. I thought to myself that since I was suffering so much in the Himalayas, I deserved a reward. So I ate all the rice there. I even snatched and ate the cookies and sugar cubes intended for the pack horses."
Standing 163 cm tall and weighing 54 kg, her body mass index (BMI) is approximately 20.3—placing her firmly on the leaner side of the normal weight range (18.5 to 24.9). Nevertheless, she appeared caught off guard by the rapid weight gain following such intense physical exertion. Her experience highlights a fundamental biological reality: weight loss is ultimately determined not by how much you exercise, but by the balance between energy consumed and energy expended.
Why Weight Rebounds After Dieting
Regaining weight after significant loss—commonly known as the "yo-yo effect"—is a frequent hurdle that stems from biological adaptation rather than a simple lack of willpower. When calories are drastically reduced, the body shifts into energy-preservation mode to replenish perceived deficits.
When calorie intake drops sharply, the metabolic rate slows down to conserve energy while hunger signals intensify. Rapid weight loss often reduces muscle mass alongside fat, lowering the body's basal metabolic rate. As a result, a person burns fewer calories at rest, making weight regain much easier even when consuming standard portion sizes.
In essence, the human body does not interpret rapid weight loss as a positive change. When weight drops below a long-held baseline, physiological mechanisms trigger energy storage as a survival response.
Energy Balance and the "Himalayan Paradox"
Koo’s experience of gaining weight despite walking 16 hours a day underscores a key principle of nutrition: body weight is governed less by exercise alone than by daily net energy balance.
Like a vehicle, the body consumes fuel (calories) through movement. However, if more fuel is added than burned, the excess is stored as fat. Even during extreme physical activity, weight will increase if caloric intake exceeds expenditure. In Koo’s case, the physical demands of high-altitude trekking triggered a massive increase in appetite, leading her to consume more energy than she burned.
Managing Post-Workout Appetite
Many people experience heightened appetite after physical activity, leading to "compensatory eating"—unconsciously consuming extra calories that equal or exceed what was burned. Studies indicate that increased appetite and reward eating are primary reasons why exercise alone often yields less weight loss than expected.
To prevent post-workout weight regain while maintaining physical activity, health experts recommend four practical eating strategies:
1. Avoid "reward eating" Reaching for high-calorie treats under the assumption that exercise canceled them out can quickly negate caloric deficits. The calories burned during 40 to 50 minutes of walking can easily be offset by a single sugary drink or snack.
2. Prioritize post-workout protein Consuming protein after exercise supports muscle repair and preserves lean muscle mass. Options like eggs, tofu, chicken breast, fish, and Greek yogurt promote satiety and prevent muscle loss.
3. Include complex carbohydrates Sustainable habits are far more effective than extreme restriction. Carbohydrates are essential after intense physical exertion, but complex options like brown rice, sweet potatoes, and fruit are preferable to refined sugars, white bread, or cookies.
4. Distinguish true hunger from psychological craving Immediate post-exercise hunger is often psychological or habit-driven rather than a true energy deficit. Drinking water first and consuming a balanced meal rich in protein and fiber helps determine if additional calories are truly needed.
