Mechanisms of action of GLP-1 and metabolic effects
The use of GLP-1 analogues has developed widely in recent years in the management of type II diabetes and obesity. GLP-1 (Glucagon-Like Peptide-1) is an intestinal hormone secreted physiologically by enteroendocrine cells, with a postprandial increase. This hormone exerts a pleiotropic action involving several organs and systems 1.
Its main effects are well established: stimulation of insulin secretion, inhibition of glucagon, slowing of gastric emptying, and increased satiety via a central action. GLP-1 analogues amplify these mechanisms by prolonging receptor activation, allowing for improved glycemic control and a significant reduction in body mass.
Clinical data show weight loss ranging from 5.8 to 17.3% over periods of 56 to 72 weeks 2. In obese patients, this loss primarily targets the reduction of fat mass, which is implicated in a chronic inflammatory state associated with numerous metabolic complications 3.
However, this weight loss is not exclusively linked to fat mass. Studies indicate that approximately 25 to 39% of the loss corresponds to fat-free mass, including muscle mass 4. This muscle decrease can lead to impaired functional capacities, a reduction in basal metabolism, and promote sarcopenic obesity 5.
Sarcopenic obesity: a point of vigilance in GLP-1 treatments
In this context, the concept of sarcopenic obesity takes on particular importance. It is defined by the association of excess fat mass and a decrease in muscle mass and/or function, and currently constitutes a recognized clinical entity according to the joint consensus of ESPEN and EASO 8.
One of the major challenges lies in the fact that this condition can progress silently, particularly during rapid weight loss, as can be observed under treatment with GLP-1 analogues.
In this framework, the use of relative indicators becomes particularly relevant. The SMM/W (Skeletal Muscle Mass / Weight) ratio allows for the evaluation of the proportion of muscle mass in relation to total weight. A decrease in this ratio reflects an alteration in body quality, even in the presence of overall weight loss.
Thus, in a patient treated with GLP-1, weight loss associated with a decrease in SMM/W may reflect a disproportionate muscle loss and point towards a progression to sarcopenic obesity. Conversely, the stability or improvement of this ratio demonstrates qualitative weight loss, centered on fat mass.
The integration of this type of indicator therefore makes it possible to refine the clinical evaluation and guide management more precisely.
Clinical implications of muscle loss
Muscle mass loss constitutes a major challenge in the management of patients treated with GLP-1. It directly impacts energy expenditure, insulin sensitivity, and physical capacity. In the long term, it can promote weight regain and reduce the benefits of the treatment.
The simple measurement of weight does not allow for the identification of these modifications. Two patients can present similar weight loss with very different physiological evolutions. It therefore becomes necessary to integrate body composition analysis into the monitoring.
Contribution of bioimpedance
Bioimpedance allows for a detailed evaluation of body composition. It distinguishes fat mass, muscle mass, and fluid compartments. It thus constitutes a key tool for analyzing the quality of weight loss.
In particular, it allows for the identification of at-risk profiles, such as patients with low initial muscle mass, and the monitoring of changes in body compartments during treatment.
Nutritional adaptation and physical activity
Management must include an adapted nutritional strategy, particularly sufficient protein intake. Recommendations suggest an intake of 1.4 to 2.0 g/kg of fat-free mass per day in order to preserve muscle mass 6.
Physical activity, particularly muscle strengthening, is also essential to limit muscle loss and improve long-term results.
Longitudinal monitoring and patient involvement
Regular monitoring of body composition allows for the early detection of deviations, such as excessive muscle loss or stagnation of fat mass. It allows therapeutic strategies to be adjusted on an individualized basis.
Bioimpedance also constitutes a motivational lever for the patient, making visible the changes that are imperceptible on the scale. It thus promotes adherence to treatment 2.
Conclusion
GLP-1 analogues represent a major advance in the management of obesity and type II diabetes. However, their efficacy must be evaluated beyond weight, by integrating body composition.
Taking into account the risk of sarcopenic obesity, particularly via indicators like SMM/W, reinforces the value of structured monitoring.
Bioimpedance thus establishes itself as an essential tool to guide, adapt, and secure management, ensuring qualitative weight loss.
Bibliography
- Drucker DJ. Mechanisms of Action of GLP-1. Cell Metab. 2018. ↑
- Mozaffarian D et al. Nutritional priorities to support GLP-1 therapy. Am J Clin Nutr. 2025. ↑ a b
- Heymsfield SB, Wadden TA. Obesity mechanisms. N Engl J Med. 2017. ↑
- Prado CM et al. Muscle loss and weight loss. Lancet Diabetes Endocrinol. 2024. ↑
- Donini LM et al. Sarcopenic obesity definition. Obes Facts. 2022. ↑
- Morton RW et al. Protein supplementation. Br J Sports Med. 2018. ↑
- Lytvyak E et al. GLP-1 obesity study. Obesities. 2025.
- Donini LM, Busetto L, Bischoff SC, et al. ESPEN and EASO Consensus Statement. Obes Facts. 2022;15(3):321–335. ↑
