# Obesity Medicine: A Lifespan Approach

## Overview
Obesity is a chronic, relapsing, multifactorial disease affecting both children and adults with increasing prevalence worldwide. Pediatric obesity prevalence in the US: ~20% of children aged 2-19 years; adult prevalence: ~42%. Developmental origins of obesity begin in utero and early childhood, making the Med-Peds perspective uniquely valuable. Management requires a comprehensive approach integrating behavioral, pharmacologic, and surgical interventions across the lifespan.

## Definitions and Classification

### Pediatric (Ages 2-18)
**Overweight**: BMI 85th-94th percentile for age and sex. **Obesity**: BMI >= 95th percentile. **Severe obesity**: BMI >= 120% of 95th percentile or BMI >= 35 (whichever is lower) BMI z-scores used for tracking in research; percentiles used clinically. Under age 2: weight-for-length charts; no BMI-based definitions.

### Adult (Age >= 18)
**Overweight**: BMI 25-29.9 kg/m2. **Obesity Class I**: BMI 30-34.9. **Obesity Class II**: BMI 35-39.9. **Obesity Class III**: BMI >= 40. BMI does not account for muscle mass, body composition, or fat distribution. Waist circumference adds cardiovascular risk information (>102 cm men, >88 cm women)

## Developmental Origins and Risk Factors

### Early Life Programming
Maternal obesity, gestational diabetes, and excessive gestational weight gain increase offspring obesity risk. Rapid infant weight gain ("catch-up growth") in the first 2 years is a strong predictor. Breastfeeding is modestly protective. Adiposity rebound: normally occurs at age 5-6; early rebound (before age 5) predicts later obesity.

### Genetic and Epigenetic Factors
Heritability of BMI estimated at 40-70%. Monogenic obesity: rare but important (leptin deficiency, MC4R mutations, POMC deficiency, Bardet-Biedl syndrome) Syndromic obesity: Prader-Willi, Albright hereditary osteodystrophy, Beckwith-Wiedemann. Polygenic risk: >900 common variants with small individual effects. Epigenetic modifications from early environmental exposures (nutrition, stress, toxins)

### Environmental and Behavioral Factors
Energy-dense food environment, sugar-sweetened beverages. Sedentary behavior, screen time (AAP recommends <1 hour/day for ages 2-5, consistent limits for older children) Sleep deprivation (associated with obesity in both children and adults) Adverse childhood experiences (ACEs) and chronic stress. Socioeconomic disparities: obesity disproportionately affects low-income and minority populations. Food insecurity paradoxically associated with obesity.

<image>Infographic showing the developmental trajectory of obesity risk factors from prenatal period through adulthood including critical windows of intervention</image>

## Screening and Assessment

### Pediatric Screening
BMI calculated and plotted at every well-child visit starting at age 2. Growth chart trajectory more informative than single measurements. Screen for comorbidities when BMI >= 85th percentile: fasting lipids, glucose, ALT, blood pressure. Evaluate for secondary causes if obesity is early-onset (<5 years), severe, or accompanied by developmental delay, short stature, or dysmorphic features.

### Adult Screening
BMI at every primary care visit. Waist circumference measurement when BMI 25-35. Metabolic syndrome screening: fasting glucose/A1c, lipid panel, blood pressure. Screen for OSA (STOP-BANG), NAFLD (ALT), PCOS in women, hypogonadism in men. Assess for eating disorders (binge eating disorder is common and underdiagnosed)

### Motivational Interviewing Across Ages
Non-judgmental, patient-centered communication essential. Avoid stigmatizing language: use "unhealthy weight" rather than "fat" or "obese" when speaking to patients. With children: engage parents as agents of change without blaming. With adolescents: build autonomy, explore readiness for change, address body image. With adults: explore ambivalence, set collaborative goals, use reflective listening.

## Behavioral and Lifestyle Interventions

### Pediatric Approach
Family-based behavioral therapy is the cornerstone (evidence strongest for ages 6-12) Structured programs with 26+ contact hours show best outcomes. AAP 2023 guidelines emphasize intensive health behavior and lifestyle treatment (IHBLT) as first-line. Dietary focus: reduce sugar-sweetened beverages, increase fruits/vegetables, family meals, portion control. Physical activity: 60 min/day moderate-vigorous for children >= 6 years. Screen time limits and sleep hygiene.

### Adult Approach
Comprehensive lifestyle intervention: 500-750 kcal/day deficit, 150-300 min/week moderate activity. Behavioral strategies: self-monitoring, stimulus control, cognitive restructuring. Structured programs (e.g., DPP-based) with regular follow-up. Dietary patterns: Mediterranean, DASH, low-carbohydrate, and intermittent fasting all show similar modest weight loss. 5-10% weight loss produces clinically meaningful improvements in metabolic parameters.

<image>Staged approach to obesity management in pediatrics showing escalation from prevention counseling through intensive behavioral therapy, pharmacotherapy, and bariatric surgery based on BMI severity and age</image>

## Pharmacotherapy

### Pediatric Pharmacotherapy (Ages 12+)

| Agent | Approved Age | Weight Loss | Key Notes |
|-------|-------------|-------------|-----------|
| Semaglutide (Wegovy) | ≥12 years | ~16% body weight | STEP TEENS trial |
| Liraglutide (Saxenda) | ≥12 years | ~5% BMI reduction | GLP-1 RA, daily injection |
| Phentermine | ≥16 years | Variable | Short-term only (max 12 weeks) |
| Orlistat | ≥12 years | Modest | GI side effects limit use |
| Setmelanotide | ≥6 years | Variable | Only for monogenic obesity (POMC, PCSK1, LEPR) |

**Semaglutide (Wegovy)**: FDA-approved for ages >= 12 with obesity; ~16% body weight reduction in STEP TEENS trial. **Liraglutide (Saxenda)**: FDA-approved for ages >= 12; ~5% BMI reduction. **Phentermine**: FDA-approved for ages >= 16 (short-term, max 12 weeks) **Orlistat**: FDA-approved for ages >= 12; limited efficacy and GI side effects limit use. **Setmelanotide**: for rare monogenic obesity (POMC, PCSK1, LEPR deficiency); ages >= 6. AAP 2023 guidelines recommend offering pharmacotherapy to children >= 12 with obesity alongside behavioral intervention.

### Adult Pharmacotherapy
**Semaglutide 2.4 mg weekly**: ~15-17% weight loss; also cardiovascular benefit (SELECT trial) **Tirzepatide (Zepbound)**: dual GIP/GLP-1 agonist; ~20-22% weight loss in SURMOUNT trials. **Phentermine-topiramate ER**: ~10% weight loss; contraindicated in pregnancy (topiramate teratogenicity) **Naltrexone-bupropion**: ~5-6% weight loss; avoid in seizure disorders, eating disorders. **Orlistat**: ~3-5% weight loss; GI side effects, fat-soluble vitamin malabsorption. Weight regain is expected after medication discontinuation — chronic treatment paradigm. Cost and insurance coverage remain major barriers.

### Special Considerations
GLP-1 agonists: nausea/vomiting most common side effect; rare risk of pancreatitis, gallbladder disease. Thyroid C-cell tumor signal in rodents (not confirmed in humans); avoid in MEN2 or medullary thyroid cancer history. Adolescents on GLP-1 agonists need monitoring of growth, nutritional adequacy, and psychological impact. Contraception counseling for adolescent females (GLP-1 agonists may reduce oral contraceptive efficacy)

## Bariatric and Metabolic Surgery

### Pediatric Bariatric Surgery
AAP and ASMBS recommend evaluating adolescents >= 13 with severe obesity (BMI >= 40 or >= 35 with comorbidities) for metabolic surgery. **Sleeve gastrectomy**: most commonly performed in adolescents; ~25-30% total weight loss. **Roux-en-Y gastric bypass**: greater weight loss and diabetes remission but higher complication rate. Teen-LABS data: durable weight loss at 5-8 years, significant improvement in comorbidities. Nutritional monitoring critical: iron, B12, calcium, vitamin D, folate. Psychosocial screening mandatory; patients need lifelong follow-up.

### Adult Bariatric Surgery
Indications: BMI >= 40 or BMI >= 35 with comorbidities (2022 ASMBS/IFSO guidelines lowered to BMI >= 35 or >= 30 with comorbidities) Sleeve gastrectomy surpassed RYGB as most common procedure. T2DM remission rates: 60-80% at 5 years. Mortality benefit demonstrated in long-term cohort studies. Consider in patients who have not achieved adequate weight loss with behavioral and pharmacologic therapy.

<image>Anatomical diagrams comparing sleeve gastrectomy and Roux-en-Y gastric bypass with key physiologic effects including gut hormone changes, caloric restriction, and malabsorption</image>

## Comorbidity Management

### Metabolic Complications
Type 2 diabetes: increasingly diagnosed in adolescents (TODAY trial showed aggressive beta-cell decline in youth) Dyslipidemia: lifestyle first; statins for high-risk pediatric patients >= 10 years. Hypertension: percentile-based in children; treat if stage 2 or stage 1 with target organ damage. NAFLD/MASLD: weight loss is the primary treatment; no approved pharmacotherapy in children.

### Other Comorbidities
Obstructive sleep apnea: screen with polysomnography; CPAP or weight loss. PCOS in adolescent and adult females. Slipped capital femoral epiphysis and Blount disease in obese children. Depression and anxiety: bidirectional relationship with obesity. Weight stigma and bullying contribute to psychological morbidity.

## Clinical Pearls
BMI percentiles plateau at higher values; a child at the 99th percentile can gain substantial weight without a change in percentile — use percent of the 95th percentile or absolute BMI for severe obesity tracking. Early-onset severe obesity (before age 5) with hyperphagia warrants genetic testing (leptin, MC4R, Prader-Willi) Weight regain after GLP-1 agonist discontinuation is the rule, not the exception — counsel patients about chronic disease management. Bariatric surgery in adolescents has comparable or better outcomes than in adults; delay may worsen comorbidities. Screen all obese children for NAFLD with ALT starting at age 9-11 (or earlier if risk factors present) The language used to discuss weight profoundly affects patient engagement; "person-first" language is recommended.

<image>Flowchart for evaluation of obesity in a child including when to suspect secondary or syndromic causes versus exogenous obesity based on growth pattern, developmental history, and physical examination findings</image>

## References
- Hampl SE, Hassink SG, Skinner AC, et al. Clinical Practice Guideline for the Evaluation and Treatment of Children and Adolescents with Obesity. Pediatrics. 2023;151(2):e2022060640.
- Weghuber D, Barrett T, Barrientos-Perez M, et al. Once-Weekly Semaglutide in Adolescents with Obesity. N Engl J Med. 2022;387(24):2245-2257.
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205-216.
- Inge TH, Courcoulas AP, Jenkins TM, et al. Five-Year Outcomes of Gastric Bypass in Adolescents as Compared with Adults. N Engl J Med. 2019;380(22):2136-2145.
- Lister NB, Baur LA, Felix JF, et al. Child and Adolescent Obesity. Nat Rev Dis Primers. 2023;9(1):24.