Recent photos of Lee Su-hyun of AKMU (a sibling duo) have been released, bringing renewed attention to her process of losing approximately 30㎏.
Amid this, expectations also emerged that simply following morning fasted exercise would make weight loss faster.
Are using more fat during exercise and losing more body fat actually the same thing?
3-Line Summary
1. Lee Su-hyun’s fasted cardio drew attention
2. The proportion of fat used during exercise may increase
3. It is difficult to conclude weight loss based solely on whether one is fasting
The Sequence of Weight Loss That One Photo Does Not Show
On the 1st, Lee Su-hyun uploaded several photos of her summer daily life to social media (SNS). Photos showing her wearing items including a floral blouse and jeans drew attention to how her clothing fit differently after losing weight. However, current weight, the speed of weight loss, and health status cannot be determined from photos alone. This is because a photo conveys how someone looked at one point in time, not the entire weight-loss process.
According to a report by the Dong-A Ilbo, Lee Su-hyun previously said that she had lost approximately 30㎏ from her highest weight. The same report described how she changed her eating habits and gradually increased her activity level after going through a period when her weight had increased significantly. Even if fasted cardio is highlighted in recent photos, that exercise alone was not the starting point of the weight loss that has been reported.
Lee Su-hyun previously said that she binge-ate to the point of ordering delivery food every day during a difficult period, and that her weight also rose rapidly. Afterward, during the first year, she reportedly reduced delivery food and ate healthy meals, losing approximately 10㎏ without any particular exercise. Beginning exercise in earnest came at the next stage.
After starting exercise, she reportedly adapted to a vegetable-centered diet prepared by a trainer and, during a period of living in training camp, combined swimming, badminton, and running in a fasted state at 7 a.m. She also reportedly added more exercise when her activity level was insufficient and switched to dancing when she became bored, continuing to stay active. Fasted cardio was one scene in this flow, not an answer that can single-handedly explain the loss of 30㎏.
Lee Su-hyun said, in essence, that she did not want people to view her method in fragments and simply follow it. It is important that the process had a particular timing and sequence that she herself mentioned. If one takes out only the exercise from the final stage, when the results became noticeable, it is easy to overlook the preceding changes in eating habits and the time her body took to adapt.
The Scope of the Claim That More Fat Is Used While Fasting
Fasted cardio generally refers to doing aerobic exercise such as walking, running, or swimming before breakfast, after not eating overnight. When fasting, insulin levels are lower than after a meal, and the amount of carbohydrates available for the body to use is relatively smaller. As a result, the proportion of fat used as an energy source during exercise may increase.
The research review introduced by the Dong-A Ilbo also explains that the amount of fat oxidation during exercise may increase with aerobic exercise performed before eating. This finding concerns which fuel was used more during the exercise itself. If the expression “burn more fat” is immediately changed into “lose more body fat,” changes occurring during exercise and long-term weight-loss results become conflated as though they mean the same thing.
In a study comparing women who performed aerobic exercise while restricting calories, both the fasted-exercise group and the post-meal exercise group lost weight and body fat, but there was reportedly no significant difference between the two groups. An analysis of a 2025 randomized clinical trial involving one-time exercise in healthy adults also introduced the conclusion that fasted exercise cannot necessarily be considered better than post-meal exercise for blood sugar or fat metabolism.
Conversely, a research review has also found that eating before exercise may help performance when exercising for a long time or at a high intensity. Even if someone begins exercising while fasted, if a drop in energy forces them to reduce the duration or intensity, it is difficult to call that exercise more efficient based only on the proportion of fat used. Exercise performance is also a condition that should be considered together in the weight-loss process.
Lee Su-hyun’s Changes That Stand Out Before “Fasting”
What stands out in Lee Su-hyun’s case is the sequence of changes, rather than whether she was fasting. There was first a period in which she reduced delivery food and continued eating healthy meals, followed by additions to the amount and types of exercise. The fact that she mixed badminton and dancing into swimming and running, rather than insisting only on swimming and running, can also be understood as a way to continue being active.
When losing weight, it is easy to choose either fasting or exercising after eating as though one of them were the only correct answer. However, both the research presented in the reports and Lee Su-hyun’s process point to the importance of overall daily intake and expenditure, as well as continuing exercise consistently. Fasted exercise is simply one available option; it has not been established as a method that promises faster weight loss for everyone.
In particular, if dizziness or severe fatigue occurs while exercising in a fasted state, it is not something to push through. The report suggested lowering the exercise intensity in such cases or switching to exercise after eating. Changes in a photo may provide motivation, but they are not grounds to take priority over the body’s signals.
The biggest point of caution in the attention surrounding this case is allowing the single word “fasted” to come to represent Lee Su-hyun’s entire process. The reported details include dietary adjustments, gradual increases in exercise volume, and changes in exercise methods. If the goal is body-fat loss, it is more important to first consider an eating and activity pattern that can be sustained than to focus on one exercise time.
References
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