Animedix

Obesity (E66.9)

Advancements in the mechanistic understanding of obesity have shifted the field from a simplistic energy-imbalance paradigm to a systems-level model integrating hypothalamic nutrient sensing, adipose tissue immunometabolism, gut–brain incretin signaling, and peripheral organ cross-talk. Central melanocortin circuitry—particularly POMC/CART and AgRP/NPY neurons within the arcuate nucleus—has emerged as a core regulatory hub, with downstream MC4R signaling validated genetically and pharmacologically as a critical node. Peripheral hormonal signals including GLP-1, GIP, amylin, PYY, leptin, and insulin converge on these networks, refining appetite, satiety, and energy expenditure. The therapeutic landscape has been transformed by incretin-based pharmacology, exemplified by GLP-1 receptor agonists such as Semaglutide and dual GIP/GLP-1 agonists like Tirzepatide, which demonstrate unprecedented weight reduction via synergistic central and peripheral mechanisms. Next-generation approaches include triple agonists (GLP-1/GIP/glucagon), amylin analogs, MC4R agonists for monogenic obesity, mitochondrial uncoupling modulation, beige/brown adipocyte thermogenesis targets (e.g., UCP1 regulation), FGF21 analogs, and gene-based interventions addressing leptin–melanocortin pathway defects. Increasing recognition of adipose tissue macrophage polarization, inflammasome activation, and fibrosis has also positioned immunometabolic pathways as modifiable nodes. Precision medicine efforts now incorporate polygenic risk scores, metabolomic phenotyping, and microbiome signatures to stratify responders, reflecting a shift toward pathway-guided and temporally tuned interventions rather than uniform caloric restriction strategies.

Causes

The etiology of obesity is multifactorial, arising from the interaction of genetic susceptibility, epigenetic programming, neuroendocrine regulation, environmental exposure, and socio-behavioral factors. Genome-wide association studies have identified polygenic contributions—most prominently variants in FTO and melanocortin pathway genes (e.g., MC4R)—that influence appetite regulation, energy expenditure, and reward circuitry. Rare monogenic forms, such as leptin or POMC deficiency, underscore the central role of hypothalamic signaling in body weight homeostasis. Epigenetic modifications driven by in utero nutrition, early-life stress, and chronic overnutrition alter transcriptional regulation of adipogenesis, mitochondrial function, and inflammatory pathways, contributing to long-term metabolic set-point shifts. Environmentally, hyper-palatable ultra-processed foods, circadian disruption, sleep deprivation, endocrine-disrupting chemicals, and sedentary behavior perturb homeostatic feedback loops between adipose tissue, liver, skeletal muscle, pancreas, and the central nervous system. Additionally, alterations in the gut microbiome influence caloric extraction, bile acid signaling, and incretin secretion, further modulating host metabolism. Increasingly, obesity is conceptualized not simply as excess adiposity, but as a dysregulated energy-partitioning state driven by gene–environment interaction across neuroendocrine and immunometabolic axes.

Pathophysiology

The pathophysiology of obesity reflects a chronic dysregulation of energy sensing, storage, and expenditure across neuroendocrine, metabolic, and inflammatory systems. At the central level, hypothalamic circuits—particularly POMC and AgRP neurons within the arcuate nucleus—become resistant to anorexigenic signals such as leptin and insulin, shifting the defended body-weight “set point” upward. Persistent hypernutrition promotes adipocyte hypertrophy and hyperplasia, leading to hypoxia within expanding adipose depots, activation of HIF-1α signaling, and recruitment of pro-inflammatory M1 macrophages. This drives chronic low-grade inflammation through NF-κB, JNK, and inflammasome pathways, impairing insulin receptor signaling via serine phosphorylation of IRS proteins and promoting systemic insulin resistance. Lipid overflow into liver, skeletal muscle, and pancreas results in ectopic fat deposition, mitochondrial dysfunction, and lipotoxicity, contributing to nonalcoholic fatty liver disease and β-cell stress. Dysregulated incretin signaling (GLP-1, GIP), altered bile acid receptor activation (FXR, TGR5), and gut microbiome shifts further perturb metabolic homeostasis. Simultaneously, sympathetic tone and brown adipose thermogenesis decline, reducing energy expenditure. Thus, obesity represents a maladaptive, self-reinforcing network of central leptin resistance, peripheral insulin resistance, adipose inflammation, and impaired metabolic flexibility rather than a simple imbalance between caloric intake and output.

Clinical features

The clinical features of obesity extend beyond excess body weight and reflect its multisystem metabolic and inflammatory consequences. Anthropometrically, patients present with elevated body mass index (BMI ≥30 kg/m²), increased waist circumference indicating visceral adiposity, and often progressive weight gain resistant to lifestyle intervention due to altered metabolic set points. Cardiometabolic manifestations include insulin resistance, impaired fasting glucose or type 2 diabetes, dyslipidemia (elevated triglycerides, reduced HDL), and hypertension, collectively constituting metabolic syndrome. Hepatic steatosis, obstructive sleep apnea, osteoarthritis (particularly knees and hips), gastroesophageal reflux disease, and polycystic ovary syndrome are common comorbidities. Patients may also experience dyspnea on exertion, reduced exercise tolerance, fatigue, and chronic low-grade inflammation. Psychosocial sequelae—depression, anxiety, and weight-related stigma—are prevalent and may exacerbate maladaptive eating behaviors. On examination, findings can include acanthosis nigricans (a marker of hyperinsulinemia), central adiposity, and signs of cardiovascular strain. Clinically, obesity is best conceptualized not merely as increased adipose mass, but as a chronic, relapsing, systemic metabolic disease with broad endocrine, cardiovascular, hepatic, musculoskeletal, and neurobehavioral manifestations.

Diagnosis

The diagnosis of obesity is primarily clinical and anthropometric but increasingly incorporates metabolic phenotyping to characterize disease severity and complication burden. The foundational metric remains body mass index (BMI), with obesity defined as ≥30 kg/m² (class I: 30–34.9; class II: 35–39.9; class III: ≥40). However, BMI alone does not capture fat distribution or metabolic risk; therefore, waist circumference and waist-to-height ratio are used to assess visceral adiposity, which more strongly correlates with cardiometabolic risk. Advanced evaluation includes assessment for obesity-related complications such as type 2 diabetes, dyslipidemia, hypertension, metabolic dysfunction–associated steatotic liver disease (MASLD), obstructive sleep apnea, and cardiovascular disease. Laboratory testing typically includes fasting glucose or HbA1c, lipid profile, liver enzymes, and sometimes fasting insulin or HOMA-IR for metabolic characterization. In selected cases, body composition analysis (DEXA, bioimpedance), resting energy expenditure testing, or genetic testing for monogenic obesity syndromes may be appropriate. Contemporary frameworks such as the Edmonton Obesity Staging System (EOSS) further stratify patients based on metabolic, functional, and psychological impact rather than weight alone, reflecting a shift toward complication-centric and precision-oriented diagnosis.

Mechanism of action videos

Biological pathways

  • cGMP-PKG signaling pathway
  • Variant SLC6A14 may confer susceptibility towards obesity
  • Thermogenesis
  • Serotonergic synapse
  • Regulation of lipolysis in adipocytes
  • Calcium signaling pathway
  • Primary bile acid biosynthesis
  • PPAR signaling pathway
  • Oxidative phosphorylation
  • Neuroactive ligand-receptor interaction
  • Neuroactive ligand signaling
  • JAK-STAT signaling pathway
  • Insulin signaling pathway
  • IL1 and megakaryocytes in obesity
  • Growth hormone synthesis, secretion and action
  • Glycerolipid metabolism
  • Glutamatergic synapse
  • Incretin synthesis, secretion, and inactivation
  • GABAergic synapse
  • Fatty acid degradation
  • FTO obesity variant mechanism
  • Dopaminergic synapse
  • Defective ACTH causes obesity and POMCD
  • Citrate cycle (TCA cycle)
  • Cholinergic synapse
  • Arachidonic acid metabolism
  • Adipocytokine signaling pathway
  • Adrenoceptors
  • Adrenaline signalling through Alpha-2 adrenergic receptor
  • Amine ligand-binding receptors
  • GPCR ligand binding
  • Adipogenesis
  • Class A/1 (Rhodopsin-like receptors)
  • Synthesis, secretion, and inactivation of Glucagon-like Peptide-1 (GLP-1)
  • GPCR downstream signalling
  • G alpha (s) signalling events
  • Signaling by GPCR
  • Peptide hormone metabolism
  • Transcriptional Regulation by MECP2
  • MECP2 regulates transcription factors

Clinical trials

  • Tirzepatide With Progestin Intrauterine Device to Treat Endometrial Hyperplasia and Grade 1 Endometrial Cancer in Overweight and Obese Women
  • A Phase 3 Randomized, Double-blind, Placebo-controlled Study to Evaluate the Impact of Maridebart Cafraglutide on Cardiovascular Outcomes in Participants With Atherosclerotic Cardiovascular Disease and Overweight or Obesity
  • A Randomized, Double-blind, Placebo-controlled, Dose-escalation Phase I Study on the Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of SHR-2906 Injection in Healthy Subjects With a Single Dose and in Obese Patients With Multiple Doses
  • A Phase 3 Randomized, Double-blind, Placebo-controlled Study to Evaluate the Efficacy, Safety, and Tolerability of Maridebart Cafraglutide in Adult Participants With Obstructive Sleep Apnea Not on Positive Airway Pressure Therapy and Living With Overweight or Obesity (MARITIME-OSA-2)
  • A Phase 3 Study to Investigate the Efficacy and Safety of Orforglipron Once Daily in Participants Who Have Obesity or Overweight and Osteoarthritis of the Knee: A Multicenter, Randomized, Double-Blind, Parallel-Arm, Placebo-Controlled Trial
  • A Master Protocol to Investigate the Efficacy and Safety of Orforglipron Tablet Once Daily Compared With Placebo in Female Participants With Stress Urinary Incontinence Who Have Obesity or Overweight
  • Phase II Trial of the Combination of Alpha-lipoic Acid and Mirabegron in Women and in Men With Obesity
  • Prospective Cohort Study to Evaluate the Efficacy, Safety, and Tolerability of Tirzepatide in Real-World Conditions in Persons With Obesity Without Diabetes and Type 2 Diabetes Mellitus With or Without Obesity in Paraguay.
  • A Master Protocol for a Randomized, Controlled, Clinical Trial of Multiple Interventions for Chronic Weight Management in Adult Participants With Obesity or Overweight
  • A Phase 1/2, Randomized, Double-blind, Placebo-controlled 2-part Study of the Safety, Tolerability, Efficacy, Pharmacokinetics, and Pharmacodynamics of Single Dose ALN-4324 in Overweight to Obese Adult Healthy Volunteers and Multiple Dose ALN-4324 in Overweight to Obese Patients With Type 2 Diabetes Mellitus (T2DM)
  • Efficacy and Safety of NNC0487-0111 s.c. Once-weekly in Participants With Overweight or Obesity, and Knee Osteoarthritis (AMAZE 5)
  • A Phase 3 Randomized, Double-Blind, Placebo-Controlled Study to Investigate the Efficacy and Safety of Once Weekly Eloralintide in Adult Participants With Persistent Obesity or Overweight Treated With a Weekly Incretin, With and Without Type 2 Diabetes
  • A Phase 4, Prospective, Open-Label, Single Arm Study to Assess the Effectiveness of Tirzepatide After Initiation of Ixekizumab in Adult Participants With Moderate-to-Severe Plaque Psoriasis and Obesity or Overweight in Clinical Practice
  • A Phase 3 Randomized, Double-Blind, Placebo-Controlled Study to Investigate the Efficacy and Safety of Once Weekly Eloralintide in Adult Participants With Obesity or Overweight, Without Type 2 Diabetes
  • A Phase 3 Randomized, Double-blind, Placebo-controlled Study to Evaluate the Efficacy and Safety of Maridebart Cafraglutide on Mortality and Morbidity in Participants Living With Heart Failure With Preserved or Mildly Reduced Ejection Fraction and Obesity (MARITIME-HF)
  • A Phase 1/2, Randomized, Double-blind, Placebo-controlled, Study of the Safety, Tolerability, Efficacy, Pharmacokinetics, and Pharmacodynamics of ALN-2232 as Monotherapy and Co-initiated With Tirzepatide in Adult Participants With Obesity
  • A Phase 3 Randomized, Double-Blind, Placebo-Controlled Study to Investigate the Efficacy and Safety of Once Weekly Eloralintide in Adult Participants With Obesity or Overweight, and Type 2 Diabetes
  • A Study Investigating the Pharmacokinetic Properties, Safety and Tolerability of NNC0487-0111 in Participants With Various Degrees of Hepatic Impairment and Participants With Normal Hepatic Function
  • A Phase 3 Randomized, Double-blind, Placebo-controlled Study to Evaluate the Efficacy, Safety, and Tolerability of Maridebart Cafraglutide in Adult Participants With Obstructive Sleep Apnea on Positive Airway Pressure Therapy and Living With Overweight or Obesity
  • Preoperative Tirzepatide for Bariatric Surgery
  • A Master Protocol for Phase 3 Randomized, Double-Blind, Placebo-Controlled Studies to Investigate the Efficacy and Safety of Once Weekly Eloralintide in Adult Participants With Osteoarthritis Knee Pain, and Obesity or Overweight (ENLIGHTEN-4)
  • A Master Protocol for Phase 3 Randomized, Double-Blind, Placebo-Controlled Studies to Investigate the Efficacy and Safety of Once Weekly Eloralintide in Adult Participants With Moderate to Severe Obstructive Sleep Apnea, and Obesity or Overweight
  • A Phase 3b Study to Investigate the Efficacy and Safety of Different Retatrutide Dose Escalation Schemes in Participants Without Type 2 Diabetes Who Have Obesity or Overweight: A Randomized, Controlled, Double-Blind Trial
  • A Phase 2, Parallel-Group, Double-Blind, Placebo-Controlled Study to Investigate Weight Reduction With Macupatide and Eloralintide, Alone or in Combination, in Adult Participants With Obesity or Overweight and With Type 2 Diabetes
  • A Phase 2, Multicenter, Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Efficacy and Safety of Oral KAI-7535 in Adult Participants Living With Obesity or Overweight With at Least 1 Weight-Related Comorbidity
  • Efficacy and Safety of Ixekizumab or Ixekizumab Concomitantly Administered With Tirzepatide in Adult Participants With Active Psoriatic Arthritis and Obesity or Overweight: A Phase 3b, Randomized, Multicenter, Open-Label Study (TOGETHER-PsA)
  • A Phase 1b Study to Assess the Safety, Tolerability, Pharmacokinetics, Immunogenicity, and Pharmacodynamics of Multiple Subcutaneous Doses of ABBV-295 in Adult Subjects With Obesity
  • Efficacy and Safety of NNC0487-0111 s.c. Once-weekly in Participants With Obesity (AMAZE 1)
  • A Phase 2, Parallel-Group, Double-Blind Study to Investigate Weight Management With LY3549492 Once Daily Compared With Placebo in Adult Participants With Obesity or Overweight
  • SHAPE-ENDO (Strategic Hormonal Approach & Prehabilitation in Endometrial Cancer): A Low-Intervention, Single-Arm, Non-Randomized Clinical Trial of Multimodal Metabolic and Surgical Optimization in Patients With Atypical Endometrial Hyperplasia or Early-Stage Endometrial Cancer and BMI ≥40 kg/m²
  • A Randomized, Double-blind, Placebo-controlled Phase 2 Trial to Assess Efficacy, Safety, and Tolerability of RO7204239 in Combination With Tirzepatide in Participants With Obesity or Overweight With At Least One Weight-related Comorbidity
  • Efficacy and Safety of Tirzepatide Once Weekly Versus Placebo for the Treatment of Obesity and Weight-Related Comorbidities in Adolescents: A Randomized, Double-Blind, Placebo- Controlled Trial (SURMOUNT-ADOLESCENTS-2)
  • A Phase 3, Multicenter, Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Study Evaluating the Efficacy and Safety of Tirzepatide Once Weekly Compared to Placebo in Adult Participants With Type 1 Diabetes and Obesity or Overweight
  • A Phase 3, Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Efficacy and Safety of KAI-9531 Administered Once Weekly in Participants Living With Obesity or Overweight and Diabetes
  • A Randomized, Double-Blind, Placebo-Controlled Phase 2 Study to Evaluate the Safety and Efficacy of Pitolisant in Patients With Prader-Willi Syndrome, Followed by an Open Label Extension
  • A Phase I/II, Randomised, Single-blind, Placebo-controlled, Multiple-ascending-dose Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of AZD9550 Monotherapy and Co-administration of AZD9550 and AZD6234 in Participants Living With Obesity and Overweight With or Without Type 2 Diabetes Mellitus
  • A Phase I, Randomized, Double-blind, Placebo-Controlled Study to Evaluate the Safety, Tolerability, Pharmacokinetics, Pharmacodynamics and Immunogenicity of Subcutaneous Administration of Single Ascending Doses of HRS-5817 in Obese Participants
  • An Open-label, Fixed-sequence Study to Assess the Effect of Elecoglipron on the Pharmacokinetics of Rosuvastatin and Atorvastatin in Healthy Participants
  • An Active-comparator-controlled, Open-label, Parallel Group Study to Evaluate the Effect of Survodutide on Energy Expenditure and Fatty Acid Oxidation in Subjects With Obesity
  • Multicentre Double-blind Randomized Clinical Trial Assessing Efficacy and Safety of Exenatide in the Treatment of Hypothalamic Obesity After Craniopharyngioma Therapy

Therapeutic area: Metabolic