GLP-1 receptor agonists, including semaglutide and liraglutide, are increasingly recognised for their effects on body composition, particularly visceral fat—the metabolically active fat surrounding internal organs. Originally developed for type 2 diabetes management, these injectable medicines work by mimicking natural GLP-1 hormone, reducing appetite and caloric intake. Clinical studies demonstrate that GLP-1 medicines can reduce visceral adipose tissue as part of overall weight loss, offering potential benefits for cardiovascular and metabolic health. In the UK, access is governed by NICE guidance, with specific criteria for diabetes management and weight loss indications. This article examines the evidence, eligibility, expected outcomes, and safety considerations for GLP-1 therapy.

What Are GLP-1 Medicines and How Do They Work?

Glucagon-like peptide-1 (GLP-1) receptor agonists are a class of medicines originally developed for type 2 diabetes management but increasingly recognised for their effects on body composition, including visceral fat reduction. These injectable medicines mimic the action of naturally occurring GLP-1, a hormone released by the intestine in response to food intake.

The mechanism of action involves several physiological pathways. GLP-1 receptor agonists bind to GLP-1 receptors in the pancreas, enhancing glucose-dependent insulin secretion whilst suppressing glucagon release. Crucially, they also act on receptors in the brain—particularly in the hypothalamus and brainstem—to reduce appetite and increase satiety. This leads to decreased caloric intake, which is the primary driver of weight loss. Additionally, these medicines slow gastric emptying, prolonging the feeling of fullness after meals.

Currently licensed GLP-1 receptor agonists in the UK include semaglutide (Ozempic for diabetes, Wegovy for weight management), liraglutide (Victoza for diabetes, Saxenda for weight management), dulaglutide (Trulicity), and exenatide (Byetta, Bydureon). The newer dual-action agent tirzepatide (Mounjaro) targets both GLP-1 and GIP receptors and is licensed in the UK for type 2 diabetes management.

Regarding visceral fat specifically, clinical studies suggest that GLP-1 medicines can lead to reductions in visceral adipose tissue as part of overall weight loss. Visceral fat—the metabolically active fat surrounding internal organs—is strongly associated with cardiovascular disease, type 2 diabetes, and metabolic syndrome. The reduction in visceral fat appears to occur primarily through sustained caloric deficit, though research continues to elucidate whether there are additional direct metabolic effects on adipose tissue beyond weight loss alone.

Who Can Access GLP-1 Treatment in the UK?

Access to GLP-1 receptor agonists in the UK is governed by NICE guidance and NHS commissioning policies, which differ depending on whether the indication is diabetes management or weight loss.

For type 2 diabetes, NICE guideline NG28 recommends GLP-1 receptor agonists in specific circumstances, including:

• As part of triple therapy (with metformin and either a sulfonylurea or pioglitazone) when dual therapy with metformin and another oral drug has not achieved adequate glycaemic control

• As part of triple therapy with metformin and a sodium-glucose cotransporter 2 (SGLT2) inhibitor if certain criteria are met

• In combination with insulin, with or without other antidiabetic drugs

Treatment should be continued only if there is a beneficial metabolic response (reduction of at least 11 mmol/mol in HbA1c and weight loss of at least 3% at 6 months).

For weight management in adults without diabetes, NICE Technology Appraisals recommend:

• Liraglutide 3.0 mg (Saxenda): For adults with a BMI of at least 35 kg/m² (or at least 32.5 kg/m² in people from certain ethnic groups) and at least one weight-related comorbidity, who are referred to and receiving specialist weight management services. Treatment should be discontinued if weight loss is less than 5% after 12 weeks on the full 3.0 mg daily dose.

• Semaglutide 2.4 mg (Wegovy): For adults with at least one weight-related comorbidity and a BMI of at least 35 kg/m² (or at least 30 kg/m² in exceptional circumstances). Treatment should be discontinued if weight loss is less than 5% after 12 months.

Both weight management treatments should be prescribed within specialist weight management services alongside a reduced-calorie diet and increased physical activity. NHS availability is subject to local commissioning decisions and supply constraints. Patients should be under regular clinical review to monitor efficacy, tolerability, and cardiovascular risk factors.

Expected Results and Timeline for Visceral Fat Reduction

Clinical trial data provide evidence for the timeline and magnitude of weight loss with GLP-1 receptor agonists, though individual responses vary considerably.

In the landmark STEP trials evaluating semaglutide 2.4 mg (Wegovy), participants achieved mean weight loss of approximately 15% over 68 weeks. Similarly, the SCALE trials with liraglutide 3.0 mg showed average weight loss of 8–9% over 56 weeks. Imaging substudies have shown that visceral adipose tissue can decrease as part of this overall weight loss, though the proportion varies between individuals.

Expected timeline:

• Weeks 0–4: Dose escalation phase; modest weight loss (1–2 kg) primarily through appetite suppression and reduced caloric intake

• Months 2–6: Accelerated weight loss phase; visceral fat reduction may become measurable on imaging; improvements in metabolic markers (HbA1c, lipids, liver enzymes) often evident

• Months 6–12: Continued but decelerating weight loss; maximal effects typically achieved between 60–68 weeks

• Beyond 12 months: Weight maintenance phase; sustained visceral fat reduction requires ongoing treatment and lifestyle modification

Factors influencing response include baseline BMI, adherence to dietary changes, physical activity levels, genetic factors, and concurrent medications. Patients with higher initial visceral fat volumes may experience greater absolute reductions.

It is important to note that visceral fat cannot be directly measured without imaging techniques such as MRI or CT scanning, which are not routinely performed in clinical practice. Waist circumference reduction is a surrogate marker that may indicate visceral fat loss, along with improvements in metabolic parameters. The degree of visceral fat reduction varies between individuals, emphasising the importance of comprehensive lifestyle intervention alongside pharmacotherapy.

Safety Considerations and NHS Prescribing Guidelines

GLP-1 receptor agonists are generally well-tolerated, but prescribers and patients must be aware of common adverse effects and safety considerations outlined in MHRA guidance and product characteristics.

Common adverse effects (affecting >10% of patients) include:

• Gastrointestinal symptoms: nausea, vomiting, diarrhoea, constipation, and abdominal discomfort—usually transient and diminishing with continued use; dose escalation protocols minimise these effects

• Injection site reactions: erythema, pruritus, or mild discomfort at subcutaneous injection sites

Serious but less common risks include:

• Pancreatitis: patients should be counselled to seek immediate medical attention if experiencing severe, persistent abdominal pain radiating to the back. Treatment should be stopped if pancreatitis is suspected and not restarted if confirmed.

• Gallbladder disease: increased risk of cholelithiasis and cholecystitis associated with rapid weight loss

• Hypoglycaemia: risk is low with GLP-1 monotherapy but increases when combined with insulin or sulphonylureas; dose adjustment of concomitant medications may be necessary

• Thyroid concerns: animal studies showed thyroid C-cell tumours; UK SmPCs advise caution in patients with personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2

• Diabetic retinopathy complications: rapid glycaemic improvement may temporarily worsen retinopathy in patients with pre-existing disease

• Acute kidney injury: can occur secondary to dehydration from severe gastrointestinal side effects; renal function should be monitored if significant vomiting or diarrhoea occurs

Contraindications include pregnancy, while breastfeeding is not recommended. These medicines should be avoided in patients with severe gastrointestinal disease and previous serious hypersensitivity reactions.

NHS prescribing guidelines emphasise that GLP-1 medicines should be initiated and monitored by healthcare professionals experienced in their use. Patients should contact their GP if they experience persistent vomiting, severe abdominal pain, signs of dehydration, or symptoms of hypoglycaemia. Regular monitoring should include weight, BMI, waist circumference, blood pressure, HbA1c (in diabetic patients), and lipid profiles. Treatment should be discontinued if response criteria are not met or if intolerable adverse effects occur.

Patients and healthcare professionals are encouraged to report suspected adverse reactions via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk). Shared decision-making regarding realistic expectations, lifestyle modification requirements, and long-term treatment plans remains essential for optimal outcomes.

Frequently Asked Questions