Obesity and Metabolic Syndrome: Causes, Health Risks and Treatment

Obesity and Metabolic Syndrome: Causes, Health Risks and Treatment

Obesity is one of the defining health challenges of the 21st century. Obesity and overweight affect large numbers of adults worldwide. In China, overweight and obesity now affect approximately 50% of adults — a dramatic shift from the low prevalence of just two decades ago.

Obesity is not a lifestyle choice or a failure of willpower — it is a chronic, relapsing medical condition driven by complex interactions between genetics, environment, hormonal signalling, gut microbiome, sleep, and socioeconomic factors. It is a major risk factor for type 2 diabetes, cardiovascular disease, several cancers, non-alcoholic fatty liver disease (NAFLD), obstructive sleep apnoea, and osteoarthritis.

Effective treatment options include GLP-1 receptor agonists and dual agonists alongside nutrition and physical activity support. The expected weight loss depends on the specific medicine and individual response.

Defining Obesity

Body Mass Index (BMI)

BMI = weight (kg) ÷ height² (m²)

BMI (kg/m²)	Category
<18.5	Underweight
18.5–24.9	Healthy weight
25.0–29.9	Overweight
30.0–34.9	Obesity class I
35.0–39.9	Obesity class II
≥40.0	Obesity class III (severe)

BMI and risk in Asian populations: Metabolic risk may occur at lower BMI, and risk varies between populations. The WHO expert consultation identified BMI 23 and 27.5 kg/m² as additional public-health action points, rather than universal replacement definitions of overweight and obesity for all Asian populations. Assessment should use the applicable local guidance and individual clinical risk.

Central (Abdominal) Obesity

BMI does not distinguish fat distribution. Visceral adiposity — fat deposited within and around abdominal organs — is metabolically active and more harmful than subcutaneous fat. Measured by waist circumference:

• Men: waist ≥94 cm (Europe) / ≥90 cm (Asia): increased risk; ≥102 cm: high risk
• Women: waist ≥80 cm (Europe) / ≥80 cm (Asia): increased risk; ≥88 cm: high risk

Visceral fat produces pro-inflammatory adipokines, fatty acids, and cytokines that drive insulin resistance, dyslipidaemia, hypertension, and endothelial dysfunction — the foundations of cardiovascular risk.

The Metabolic Syndrome

Metabolic syndrome is a cluster of cardiometabolic risk factors that commonly occur together, driven by central obesity and insulin resistance. Diagnosis requires ≥3 of the following (IDF/AHA criteria):

Component	Threshold
Waist circumference	≥90 cm (men) / ≥80 cm (women) in Asians
Fasting glucose	≥5.6 mmol/L (or on diabetes medication)
Triglycerides	≥1.7 mmol/L (or on medication)
HDL cholesterol	<1.0 mmol/L men / <1.3 mmol/L women (or on medication)
Blood pressure	≥130/85 mmHg (or on antihypertensive medication)

Metabolic syndrome affects approximately 25–30% of adults globally and confers a 2× increased risk of cardiovascular events and a 5× increased risk of type 2 diabetes.

Health Consequences of Obesity

Metabolic

• Type 2 diabetes — 80% of T2DM patients are overweight or obese; adipose tissue-derived free fatty acids and inflammatory adipokines impair insulin signalling in liver, muscle, and fat
• Non-alcoholic fatty liver disease (NAFLD/MASLD) — excess fat accumulation in the liver; present in approximately 25% of the general population and 75–90% of obese individuals; can progress to non-alcoholic steatohepatitis (NASH/MASH) → cirrhosis → hepatocellular carcinoma
• Polycystic ovary syndrome (PCOS) — obesity worsens insulin resistance and androgen excess; weight loss alone can restore ovulation in many women with PCOS

Cardiovascular

• Hypertension — each 5 kg weight gain raises systolic BP by approximately 2–3 mmHg
• Dyslipidaemia — elevated triglycerides and LDL, reduced HDL
• Coronary artery disease — 2–3× increased risk
• Atrial fibrillation — obesity is an important modifiable risk factor for AF
• Heart failure — obesity cardiomyopathy; increased cardiac workload

Cancer

Higher amounts of body fat are associated with increased risk of several cancers. Examples include endometrial, post-menopausal breast and colorectal cancers, oesophageal adenocarcinoma and gastric cardia cancer. These associations are specific to tumour type and site; they do not mean that obesity causes every cancer in these organs. Proposed mechanisms include chronic inflammation, hyperinsulinaemia, sex hormone excess and adipokine signalling.

Respiratory

• Obstructive sleep apnoea (OSA) — present in 40–70% of obese individuals; intermittent nocturnal hypoxia raises cardiovascular risk
• Obesity hypoventilation syndrome — obesity with sleep-disordered breathing and persistently elevated blood carbon dioxide while awake during the day, after other causes of inadequate ventilation have been excluded; it can cause serious respiratory complications
• Asthma — obesity worsens airway inflammation and mechanical loading

Musculoskeletal

• Osteoarthritis of weight-bearing joints (knees, hips) — each 1 kg weight gain increases knee load by approximately 4 kg per step
• Gout — hyperuricaemia from increased purine turnover

Psychosocial

• Depression and anxiety (bidirectional relationship with obesity)
• Stigmatisation and discrimination
• Reduced quality of life across all domains

Treatment

Effective obesity management requires a multimodal approach combining lifestyle, behavioural support, pharmacotherapy, and surgery where indicated.

Lifestyle Intervention

Dietary modification:

• A clinician or dietitian can help agree a suitable calorie deficit and monitor progress; weight loss varies.
• Dietary approaches should be individualised, with attention to nutritional adequacy and long-term adherence.
• Low-energy and very-low-energy total diet replacement programmes require clinical support and supervision, nutritional completeness and a plan for returning to a wider range of foods. Medicines, including diabetes medicines, need clinical review before starting and adjustment when indicated. Suitability, weight loss and diabetes outcomes vary; do not start a restrictive programme or change medicines without the treating team.

Physical activity:

• 150–300 minutes/week moderate aerobic exercise (walking, cycling, swimming)
• Resistance training preserves lean mass during weight loss
• Exercise alone produces modest weight loss (3–5 kg) but substantially improves cardiovascular fitness, metabolic risk factors, and mental health independent of weight

Behavioural therapy:

• Cognitive behavioural therapy (CBT) addressing eating patterns, emotional eating, and self-regulatory skills
• Commercial and NHS behavioural programmes: sustained behaviour change requires structured support, not information alone

Pharmacotherapy

Until recently, approved weight-loss medications had modest efficacy (5–7% body weight loss). The GLP-1 receptor agonist class has transformed this landscape.

GLP-1 receptor agonists:

Semaglutide (Wegovy) — 2.4 mg weekly subcutaneous injection:

• The STEP trials: average 14.9% body weight loss at 68 weeks vs 2.4% with placebo (STEP 1)
• Reduces cardiovascular events in obese adults with established CVD (SELECT trial: 20% reduction in MACE)
• Now approved for chronic weight management (Wegovy) separately from diabetes (Ozempic)

Liraglutide (Saxenda) — 3 mg daily injection: ~8% body weight loss; approved for weight management.

Dual GIP/GLP-1 agonists:

Tirzepatide (Mounjaro/Zepbound):

• Activates both GIP and GLP-1 receptors — superior to semaglutide in head-to-head trials (SURMOUNT-5: 20.2% vs 13.7% weight loss)
• SURMOUNT-1: up to 22.5% body weight loss at 72 weeks
• FDA approved for chronic weight management (Zepbound) and T2DM (Mounjaro)

These medicines may be used long term when benefits outweigh adverse effects. Continuing, changing or stopping treatment should be discussed with the prescribing clinician; weight regain is common after stopping, but the amount varies between individuals.

Orlistat — lipase inhibitor reducing fat absorption by 30%; modest weight loss (3 kg above placebo); GI side effects limit use.

Bariatric and Metabolic Surgery

Eligibility for metabolic or bariatric surgery depends on current guidelines, BMI, metabolic disease, previous treatment and specialist assessment. Some guidelines use lower BMI thresholds for Asian patients; BMI alone does not determine suitability. A specialist team should discuss the available procedures, potential benefits and risks:

Sleeve gastrectomy — most common procedure globally; approximately 75% of excess weight lost at 2 years; reduces gastric volume by ~80%, reduces ghrelin (hunger hormone); technically simpler; lower complication rate; not reversible.

Roux-en-Y gastric bypass (RYGB) — gold standard metabolic surgery; bypasses stomach and proximal small bowel; 75–80% excess weight lost; can improve T2DM control and may lead to remission, which is not assured; procedure selection requires individual assessment; more complex; dumping syndrome risk; nutritional monitoring required lifelong.

One anastomosis gastric bypass (OAGB / mini-bypass) — gaining popularity; good efficacy; technically simpler than RYGB.

Adjustable gastric band — largely abandoned due to inferior efficacy and high reoperation rate.

Outcomes of bariatric surgery:

• T2DM remission: 60–80% (gastric bypass); 50–60% (sleeve gastrectomy)
• Hypertension remission: 60–75%
• OSA resolution: 80–85%
• Significant reduction in cardiovascular events and all-cause mortality in long-term studies
• Lifelong nutritional supplementation required (vitamin B12, iron, calcium, vitamin D)

Obesity and Metabolic Disease Care in China

China's metabolic disease and bariatric surgery centres offer:

• Comprehensive obesity assessment: BMI, body composition (DEXA or bioimpedance), metabolic panel (glucose, insulin, HbA1c, lipids, liver enzymes, uric acid), sleep study for OSA, and cardiac risk assessment
• GLP-1 medication access: semaglutide (Ozempic/Wegovy), tirzepatide (Mounjaro), and liraglutide available through specialist clinics; structured titration and monitoring
• High-volume bariatric surgery: sleeve gastrectomy, Roux-en-Y gastric bypass, and OAGB performed by experienced bariatric surgeons; laparoscopic approach standard; comprehensive pre-operative assessment and post-operative support
• Multidisciplinary metabolic team: bariatric surgeon, endocrinologist, dietitian, psychologist, and anaesthetist in a structured pre-operative programme
• Cost: care in China is generally less expensive than UK private treatment, but the hospital prices each case individually — ask us for the written quote before you commit.
• Full English care navigation from initial assessment through surgery and long-term follow-up

Contact a PriumCare care navigator to arrange an obesity medicine consultation, bariatric surgery assessment, or GLP-1 medication review.

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Medical content based on MSD Manuals and international obesity management guidelines. Evidence reviewed 2025.

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Targeted editorial source check — 26 October 2026: Only the BMI action-point distinction and obesity hypoventilation description were checked against the WHO expert consultation and ATS clinical practice guideline. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date.

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Targeted editorial source check — 26 October 2026: The dietary-supervision, surgical-eligibility and cancer-risk passages were checked against NICE dietary recommendations, ASMBS/IFSO guidance and NCI cancer-risk information. This is not a whole-article medical review and does not determine an individual treatment plan.

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Targeted editorial source check — 26 October 2026: Only the global adult-count wording and its summary, disease-risk rankings, the class-wide weight-loss estimate, medication continuation and weight regain after stopping, and the gastric-bypass remission ranking were checked against WHO obesity information, AHA atrial-fibrillation guidance, NIDDK medication information, U.S. liraglutide prescribing information, NIDDK surgical-options information and a long-term metabolic-surgery trial. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date.