I. The Mechanisms of Action of GLP-1
For several years, GLP-1 analogues have been increasingly used in the management of patients with type II diabetes or obesity, with a growing number of molecules on the market. GLP-1, for Glucagon-Like Peptide-1, is a molecule naturally and continuously secreted by cells in the intestine, with secretion peaks following food intake. It has a pleiotropic action, i.e., on several organs with different effects¹, the most notable of which are:
- An inhibition of glucagon secretion and an increase in insulin secretion, promoting a decrease in blood sugar.
- A local inhibition of gastric emptying.
- An increase in satiety through an action on the brain’s hunger regulation centers.
The goal of therapy with GLP-1 analogues is to increase these three effects by stimulating its receptor on these different organs more significantly than in a normal physiological situation. This is particularly interesting for patients with type II diabetes to limit hyperglycemia and the associated deleterious effects of the pathology, but also for obese individuals for weight loss. Indeed, several studies have shown that the loss of body mass induced by GLP-1 analogues was 5.8 to 17.3%, over a duration of 56 to 72 weeks, compared to a placebo².
In obese patients, the goal of body mass loss is to decrease fat mass because it is the cause of a pro-inflammatory environment responsible for numerous clinical complications associated with the pathology³. This loss of body weight is induced by an increase in satiety and the inhibition of gastric emptying, leading to a reduction in food intake and thus in daily caloric intake. Consequently, this places the patient in a situation of caloric deficit responsible for a decrease in body mass. However, it has been observed that about 25 to 39% of this weight loss corresponded to non-fat mass and not fat mass⁴. This loss of non-fat mass, and therefore muscle mass, can be detrimental to the patient due to the onset of sarcopenic obesity, which can impair their ability to perform daily life activities and promote a sedentary lifestyle that is harmful to their health⁵.
Based on this observation, it is therefore necessary to monitor that the loss of body mass is indeed a loss of fat mass and to maintain muscle mass during the management process.
II. The Contribution of Bioelectrical Impedance Analysis in Management during GLP-1 Analogue Therapy
As explained in the previous paragraph, the goal of therapy with GLP-1 analogues is to decrease fat mass, but the observed decrease in muscle mass also leads health professionals to maintain the latter as much as possible during management.
In this context, it is necessary, in addition, to have an adapted nutritional management characterized in particular by a high protein intake and regular resistance physical activity, i.e., weight training/muscle strengthening. In addition to this, it is also relevant to evaluate body composition by bioelectrical impedance analysis (BIA), especially muscle mass and fat mass, in order to be able to adapt the management and also to control its effects. Indeed, the evaluation of muscle mass can make it possible to detect at-risk profiles, particularly with insufficient muscle mass, and to be vigilant during follow-up.
From a nutritional point of view, a daily intake greater than 1.6 g/kg (weight)/day helps to optimize hypertrophy and the maintenance of muscle mass during weight loss⁶. However, the very high body mass of patients makes it impossible to use this figure based on weight because the protein intake would be gigantic and difficult to adhere to. For example, a 160 kg patient would have to ingest about 256 g of protein per day, which is equivalent to 1.3 kg of meat/fish/tofu or 43 eggs, which is considerable and very difficult to envision. Thus, it is more interesting to base the intake on non-fat mass in order to provide the patient with an achievable daily goal, and therefore to recommend an intake of 1.4 to 2.0 g/kg (non-fat mass)/day. If we return to the previous case, taking into account a fat mass percentage of 50%, this gives a non-fat mass of 80 kg, leading to an intake of 128 g of protein, for an intake of 1.6 g/kg/day, which is achievable with a balanced diet to which supplementation can be added. Protein intake is crucial during management to maintain muscle mass so that the observed loss corresponds to a normal readjustment of it in relation to body weight⁷.
Furthermore, monitoring body composition allows for the detection of a rapid loss of muscle mass and/or a stagnation of fat mass, leading to an adjustment of the management, whether at the medication, nutritional, and/or behavioral level. Indeed, the long-term success of this type of therapy is strongly associated with the patient’s involvement² and a loss of motivation can limit the loss of fat mass. In this context, bioelectrical impedance analysis constitutes an interesting motivational lever to maintain patient involvement by showing them the evolution of their body composition. It can also be a way to dialogue with them to investigate whether changes in daily life could be the cause of a decrease in motivation and/or the effectiveness of the treatment.
Conclusion
Therapy with GLP-1 analogues constitutes an interesting therapeutic approach for fat mass loss in the context of obesity and for glycemic control in type II diabetes. However, it can be responsible for a very significant decrease in muscle mass, which is detrimental to the patient and can be countered by nutritional management and physical activity. In this context, bioelectrical impedance analysis is relevant for evaluating body composition with the aim of guiding and controlling the management, as well as for maintaining patient involvement.
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