Prevention of loose skin after weight loss and common misconceptions about localized fat accumulation: The possibility of "targeted weight loss" based on the principles of fat cell metabolism.

Excessive skin not only affects appearance, but sagging skin is also prone to infection and even ulceration, negatively impacting health. In some cases of severe obesity, surgical removal of excess loose skin is necessary after exercise-based weight loss. Severe cases of excess skin cannot be improved by simple exercise or topical skincare products and often require surgical removal. This is not only expensive but also traumatic, causing greater suffering for obese patients. The resulting surgical scars are often unacceptable; therefore, it is crucial to minimize skin laxity during the exercise-based weight loss process.

Excessive skin laxity can be prevented in advance. In the early stages of exercise-based weight loss, obese individuals are advised to massage their abdomen for at least 30 minutes each night before bed to promote skin contraction and prevent sagging after weight loss. The massage should be gentle and the pressure even. A lubricant can be applied to the massaged area. Slowing down the rate of weight loss is also a way to avoid sagging abdominal skin. The thighs and buttocks are generally less prone to sagging skin because their circumference decreases more slowly than the abdominal circumference during exercise-based weight loss.

However, the rate of decrease in upper arm circumference is similar to that of abdominal circumference. Therefore, after exercise-induced weight loss, the upper arms are also prone to skin laxity, requiring appropriate skin massage. In addition, alternating hot and cold baths and appropriately increasing local strength training to increase muscle volume can reduce or prevent excess skin. Using medications that increase skin elasticity and promote collagen growth may aid recovery to some extent. Localized obesity refers to obesity caused by excessive fat accumulation in a specific part of the body, most commonly in the abdomen, buttocks, and thighs. The main causes of localized obesity are overnutrition, endocrine disorders, metabolic dysfunction, and especially lack of physical activity.

Some believe that the only effective way to achieve localized weight loss is through surgery, such as liposuction and fat removal. Since the 1980s, localized liposuction has become popular, offering advantages over traditional liposuction, including less trauma and less scarring. However, it also carries significant risks. Post-operative complications include sensory impairment, bruising, hematoma, edema, infection, and even life-threatening fat embolism. Unless absolutely necessary, invasive treatments are not recommended for obese patients. While humans typically have 1 to 3 billion fat cells, obese individuals can have as many as 10 billion.

Dietary fat is stored in fat cells as triglycerides. Overeating, especially during childhood and adolescence, not only causes fat cells to expand in size but also increases in number. After weight loss, fat cells only shrink in size, not in number, and these shrunken fat cells still retain the ability to expand. In other words, weight loss cannot reduce the number of fat cells. For obese patients, liposuction can remove some fat cells. While liposuction can reduce the number of fat cells, it doesn't mean that the remaining fat cells won't continue to expand.

Moderate-intensity, long-duration aerobic exercise is an effective way to reduce obesity. However, is spot reduction effective? The answer is no. This is a major misconception about exercise for weight loss. There are two main reasons for this: spot reduction consumes less energy, easily leads to fatigue, and cannot be sustained. Effective weight loss exercise needs to last for at least 30 minutes. For example, sit-ups are difficult to maintain for long periods, and the energy source during exercise is not primarily fat, making it impossible to achieve good fat loss results, let alone reduce localized fat. Practice has shown that easy and enjoyable full-body moderate-intensity aerobic exercise is the correct way to lose weight. If it's too strenuous, it means the body isn't utilizing fat oxidation for energy and cannot produce significant weight loss results.

The main energy source for fat is fatty acids in the blood. When exercise is needed, fatty acids are extracted from the blood and oxidized to provide energy. It's not about "targeting specific areas for fat loss," but rather that fat from areas with ample blood supply is first transported into the bloodstream and then delivered to the working muscles to provide energy. For example, when exercising the waist, the abdominal muscles don't just use abdominal fat for energy; they mobilize fat from throughout the body as an energy source. In this sense, there is no such thing as spot reduction through exercise.