Abstract: Semaglutide is a glucagon-like peptide-1 receptor agonist (GLP-1RA) that has revolutionized the pharmacological management of obesity. Originally developed for type 2 diabetes, it has demonstrated substantial efficacy in chronic weight management, achieving significant reductions in body weight. Beyond weight loss, semaglutide offers profound cardiometabolic benefits, including the reduction of major adverse cardiovascular events and improvements in heart failure and metabolic dysfunction-associated steatohepatitis. Its mechanism involves both central appetite regulation and peripheral metabolic effects. Despite its efficacy, challenges such as gastrointestinal adverse events, lean muscle mass loss, and weight regain upon discontinuation remain. Integrating semaglutide with Medical Nutrition Therapy (MNT) and lifestyle modifications is crucial for optimizing long-term outcomes and preserving metabolic health.
1. Introduction
Obesity is a major global health pandemic, often referred to as "globesity," and is associated with numerous chronic conditions, including type 2 diabetes (T2D), cardiovascular diseases (CVD), and osteoarthritis [2]. The management of obesity requires comprehensive strategies, and recently, second-generation anti-obesity medications (AOMs) have emerged as highly effective tools [3]. Semaglutide, a GLP-1RA, was approved by the FDA and EMA in 2021 as an adjunct to reduced calorie intake and increased physical activity for chronic weight management in adults with obesity (BMI ≥ 30 kg/m²) or overweight (BMI ≥ 27 kg/m²) with at least one weight-related comorbidity [1][2]. It represents a cornerstone of modern obesity pharmacotherapy, offering weight loss efficacy that significantly surpasses traditional lifestyle modifications alone [2][3].
2. Pharmacological Activity
The clinical efficacy of semaglutide 2.4 mg administered subcutaneously once-weekly has been extensively evaluated in the Semaglutide Treatment Effect in People with obesity (STEP) clinical trial program [2][3]. In the STEP 1 trial, participants achieved a mean weight reduction of approximately 14.9% to 16.9% over 68 weeks, compared to 2.4% with placebo [2][3]. The STEP 5 trial demonstrated that this weight loss is durable and maintained over 104 weeks [1][3]. Oral formulations of semaglutide have also shown significant weight reduction capabilities in T2D patients across the PIONEER trials [9].
Beyond weight loss, semaglutide exhibits pleiotropic benefits. The SELECT trial demonstrated a 20% reduction in the risk of major adverse cardiovascular events (MACE), including cardiovascular death, nonfatal myocardial infarction, and nonfatal stroke, in patients with overweight or obesity and pre-existing CVD [2][7]. Furthermore, semaglutide improves symptoms and physical limitations in obesity-related heart failure with preserved ejection fraction (HFpEF) [2][5]. It also shows disease-modifying potential in metabolic dysfunction-associated steatohepatitis (MASH) by promoting histological resolution of steatohepatitis [2][5], and reduces pain in knee osteoarthritis [5].
3. Molecular Mechanism of Action
Semaglutide mimics the endogenous incretin hormone GLP-1, which is naturally secreted by intestinal L-cells in response to food intake [2][3]. It exerts its effects through both central and peripheral pathways. Centrally, semaglutide accesses the brainstem, septal nucleus, and hypothalamus, directly and indirectly interacting with neural pathways involved in homeostatic (appetite, hunger, satiety) and hedonic (food preference, cravings) aspects of eating [1][2]. It activates GLP-1 receptors in the dorsal vagal complex, including the area postrema and nucleus tractus solitarius, which also play a role in nausea and emesis pathways [2].
Peripherally, semaglutide enhances glucose-dependent insulin secretion from pancreatic β-cells, suppresses glucagon release, and delays gastric emptying [1][2]. The delayed gastric emptying contributes to early satiety and fullness [2]. Additionally, semaglutide interacts with the gut microbiota; microbial metabolites like short-chain fatty acids (SCFAs) stimulate endogenous GLP-1 secretion, and semaglutide itself can modulate gut inflammation and correct high-fat diet-induced dysbiosis [2].
4. Structure-Activity Relationship (SAR)
Semaglutide is a long-acting human GLP-1 analogue that shares 94% structural homology with native GLP-1 [1][2]. Native GLP-1 has a very short half-life of approximately 2 to 3 minutes due to rapid degradation by the enzyme dipeptidyl peptidase-4 (DPP-4) [2][3]. To overcome this, semaglutide has been structurally modified by the addition of a hydrophilic spacer and a fatty acid side chain [2]. These modifications allow for reversible binding to albumin, which reduces renal clearance and protects the molecule from DPP-4 degradation [1][2]. Consequently, the half-life of semaglutide is significantly extended to approximately 155 to 184 hours (about 1 week), enabling convenient once-weekly subcutaneous administration [1][3].
5. Current Limitations
Despite its efficacy, semaglutide therapy faces several limitations. The most common adverse events (AEs) are gastrointestinal (GI) in nature, including nausea, vomiting, diarrhea, and constipation, which occur frequently during the dose-escalation phase and can lead to treatment discontinuation [1][2][4].
Another significant concern is the alteration of body composition. While semaglutide reduces fat mass, it also causes a substantial loss of lean body mass (LBM), which can account for approximately 25% of the total weight lost, raising the risk of sarcopenia and metabolic adaptation [2].
Furthermore, obesity is a chronic disease, and discontinuation of semaglutide leads to rapid weight regain. In the STEP 4 trial, participants who switched to a placebo after 20 weeks of treatment regained a significant portion of their lost weight, and cardiometabolic improvements reverted to baseline [3][6]. Other limitations include high out-of-pocket costs, variable insurance coverage, and rare but notable risks of gallbladder-related disorders (cholelithiasis) and acute pancreatitis [1][2][3].
6. Future Perspectives
To address current limitations and enhance efficacy, future strategies are focusing on combination therapies and multidisciplinary care. Combining semaglutide with other hormonal agents, such as the amylin analogue cagrilintide (CagriSema), has shown additive effects on weight control in early trials by targeting different brain regions involved in satiety [1][3].
Integrating pharmacotherapy with Medical Nutrition Therapy (MNT) is critical. Structured dietary approaches, such as the Mediterranean Diet (MD) or Very-Low-Energy Ketogenic Therapy (VLEKT), combined with adequate protein intake and resistance training, are proposed to preserve muscle mass, mitigate GI side effects, and support long-term adherence [2]. Precision medicine will also play a role, tailoring treatments based on sex-specific responses, hormonal interactions, and gut microbiota profiles to optimize therapeutic outcomes [2][4].
