Obesity has become a global public health crisis, attracting significant attention due to its association with metabolic syndrome, cardiovascular diseases, type 2 diabetes, and various cancers. Bariatric-metabolic surgery, as a long-term effective method for weight management, can significantly reduce visceral and subcutaneous fat, improving metabolic health. However, it is also crucial to recognize the postoperative decline in muscle mass and bone density, which can lead to a series of related issues, adversely affecting patients' physical health and quality of life. Given this complex clinical reality, research on postoperative body composition changes becomes particularly important. Here, the authors systematically summarize the characteristics of body composition changes at different stages after bariatric-metabolic surgery, delves into the clinical significance of body composition loss, and provides a forward-looking perspective on the future development of this field, aiming to develop more scientific and reasonable postoperative management strategies for clinical practice.