Weight Gain Algorithm

Safety

Red Flags — Endocrine Emergency, Malignancy & Cardiac Oedema

Done

Rapid weight gain + bilateral pitting ankle and leg oedema + orthopnoea + paroxysmal nocturnal dyspnoea + elevated JVP New or decompensated heart failure. → 999 if acutely breathless at rest. New presentation: NT-proBNP + ECG. NT-proBNP >2000 ng/L → specialist assessment and echocardiography within 2 weeks; 400–2000 ng/L → within 6 weeks (NICE NG106; local heart failure pathway).

Weight gain + generalised oedema + very low albumin + heavy proteinuria (frothy urine) + lipids elevated Suspected nephrotic syndrome. → Urgent assessment: urine ACR/PCR, serum albumin, renal function, lipids, BP and oedema; discuss urgently with nephrology — same day if severe oedema, acute kidney injury, thrombosis, infection or unstable. Heavy proteinuria alone does not establish the full syndrome. Renal biopsy may be required but is not automatic — it depends on age, presentation, renal function, serology and suspected cause.

Weight gain (predominantly truncal) + violaceous striae >1 cm + proximal muscle weakness + easy bruising + hypertension + hyperglycaemia Possible Cushing's syndrome. → First review all exogenous glucocorticoid exposure (oral, inhaled, topical, intra-articular, epidural and steroid-containing preparations). Then select one appropriate first-line test according to the local endocrine pathway and discuss abnormal results with endocrinology (false positives are common). Do not screen for uncomplicated obesity or weight gain.

Weight gain + severe bradycardia + cold intolerance + periorbital oedema + myxoedematous facies + reduced consciousness Myxoedema coma (severe hypothyroidism with altered consciousness). → 999/A&E and critical-care assessment. Hospital: IV hydrocortisone before or with thyroid hormone when adrenal insufficiency has not been excluded; IV levothyroxine, with liothyronine only in selected cases on specialist/critical-care advice; treat hypothermia, hypoglycaemia, hyponatraemia, infection and precipitating causes.

Abdominal swelling rather than fat gain: ascites, or a pelvic or abdominal mass (not obviously uterine fibroids) Possible ovarian or other intra-abdominal cancer. → In a woman, gynaecological cancer referral on the suspected cancer pathway without waiting for CA125 (NICE NG12, updated April 2026); ascites in anyone → urgent ultrasound, liver tests and albumin. Persistent or frequent bloating, early satiety or pelvic pain in a woman (especially aged 50 or over) → CA125 and ultrasound per NG12 (see the bloating algorithm).

Significant weight gain after starting new medications (antipsychotics, corticosteroids, insulin, sodium valproate, lithium, mirtazapine, thiazolidinediones) Drug-induced weight gain. → Medication review. Discuss weight-neutral alternatives with the prescriber — antipsychotic and mood-stabiliser changes are psychiatry-led. Monitor HbA1c, lipids, BP.

Weight gain + hypertension + diabetes + severe OSA + polycythaemia (raised haematocrit) in obese patient Obesity-related metabolic syndrome with multiple end-organ complications. → Treat each condition; cardiovascular risk assessment; weight-management medicines or bariatric assessment according to NICE eligibility and local commissioning.

Cushing's syndrome is the most frequently missed endocrine cause of weight gain in primary care — the characteristic fat distribution (truncal/central obesity with thin extremities, 'buffalo hump' of upper back, 'moon face' from supraclavicular and temporal fat pads), combined with proximal myopathy (difficulty rising from a chair without using arms), violaceous striae (wide, >1 cm, purple-red — unlike the white striae of simple obesity), easy bruising, and hypertension forms the classic Cushingoid phenotype. Exogenous corticosteroid use is by far the most common cause of Cushing's syndrome in the UK — any patient taking prednisolone, inhaled high-dose corticosteroids (particularly in combination), or topical potent steroids over large areas can develop iatrogenic Cushing's. The GP's first step: a thorough steroid exposure history (all routes — oral, inhaled, intranasal, topical, intra-articular injections). Endogenous Cushing's (ACTH-dependent — pituitary adenoma Cushing's disease, or ectopic ACTH from small cell lung cancer; ACTH-independent — adrenal adenoma or carcinoma) should be tested for only when discriminatory features are present, using one first-line test per the local endocrine pathway; discuss abnormal results with endocrinology, as false positives are common.

Diagnose

Causes of Weight Gain — Systematic Classification

Done

Lifestyle and environmental (most common)

Caloric excess relative to expenditure: ultra-processed food (high palatability, low satiety, high energy density), sedentary behaviour, reduced physical activity, sleep deprivation (increases ghrelin + reduces leptin → increased hunger), social and environmental food cues, food insecurity (cheap calorie-dense food). These factors interact with genetic predisposition. Weight gain is rarely simply "lack of willpower" — it reflects complex neurobiological, environmental, and socioeconomic drivers.

Endocrine causes

Hypothyroidism: weight gain typically modest (mainly fluid retention), often accompanied by fatigue, constipation, cold intolerance, dry skin, bradycardia, hoarse voice. TSH is the first-line test (add free T4 if pituitary disease is possible); do not attribute obesity to hypothyroidism without biochemical evidence. PCOS: insulin resistance, hyperandrogenaemia, central obesity — adult diagnosis needs 2 of: clinical/biochemical hyperandrogenism, ovulatory dysfunction, polycystic ovaries on ultrasound or raised AMH (after excluding differentials). LH/FSH not routinely required; total testosterone (± SHBG/free testosterone), HbA1c or glucose; DHEAS only if androgen excess is marked or atypical. Cushing's syndrome: exogenous (most common) or endogenous — check all steroid exposure routes. Insulinoma (rare): episodic hypoglycaemia → compensatory eating. Hypothalamic obesity (rare — after pituitary surgery, craniopharyngioma, radiotherapy).

Drug-induced weight gain

Weight gain is common with: antipsychotics (olanzapine/clozapine most potent; risperidone; quetiapine moderate), mood stabilisers (lithium, sodium valproate, carbamazepine), antidepressants (mirtazapine, TCAs, paroxetine, amitriptyline), corticosteroids (all routes), insulin (anabolic + promotes fat storage), sulfonylureas (glibenclamide, gliclazide — increase appetite), thiazolidinediones (pioglitazone — fluid retention + fat redistribution), antihistamines (chlorphenamine, cyproheptadine — H1 antagonism → appetite increase), gabapentin/pregabalin (fluid retention + increased appetite).

Other causes

Fluid retention: heart failure (see above), nephrotic syndrome, liver failure (ascites + peripheral oedema), CKD, venous insufficiency, lymphoedema, pregnancy. Smoking cessation: weight gain is common after stopping (metabolic rate + oral behaviour + improved taste). Cessation of previously prescribed amphetamines or stimulants. Age-related muscle loss (sarcopenic obesity): BMI may appear stable as fat replaces muscle.

Drug-induced weight gain is one of the most important and most frequently overlooked causes of weight gain in primary care — the GP who prescribes olanzapine 10 mg without monitoring metabolic parameters or without advising the patient about weight gain risk is setting up a preventable adverse outcome. Olanzapine and clozapine are the most potent weight-gain-inducing antipsychotics. The mechanism: H1 receptor antagonism (appetite increase and sedation), muscarinic antagonism (dry mouth → increased caloric beverages), and direct effects on hypothalamic appetite regulation. NICE CG178 (psychosis and schizophrenia — not a complete protocol for every antipsychotic indication) recommends that weight (weekly for the first 6 weeks), waist circumference, blood pressure, fasting glucose or HbA1c, and lipids are monitored: at baseline before starting any antipsychotic, at 12 weeks, at 1 year and then annually. GPs with patients on antipsychotics who have not had annual metabolic monitoring should initiate this at the next review.

Diagnose

Assessment — History, Examination & Investigations

Done

Structured weight gain history

Confirm the trajectory using previous weights and decide whether this is fat gain, fluid gain (oedema, dyspnoea, orthopnoea), pregnancy or medication-related gain. Ask about binge-eating and OSA symptoms. Timeline: onset (gradual over years vs rapid over weeks/months), trajectory (steady vs accelerating), weight at different life stages. Triggers: medication change (new drug start correlating with weight gain onset), life events (bereavement, retirement, injury limiting activity), pregnancy (inter-pregnancy weight gain), menopause (fat redistribution, reduced metabolic rate). Diet: quality and quantity of intake, eating patterns (meal skipping → compensatory eating, night eating, emotional eating), ultra-processed food frequency, alcohol units/week (high caloric content + stimulates appetite). Activity: type and frequency, reduction from previous baseline, sedentary hours per day. Sleep: duration, snoring, witnessed apnoeas (OSA — associated with weight gain and insulin resistance). PMH: diabetes, hypothyroidism, PCOS, depression. Drug history: specifically antipsychotics, steroids, insulin, valproate, mirtazapine.

Examination

Anthropometry: weight + height → BMI. Waist-to-height ratio (adults with BMI <35 where feasible): ≥0.5 increased cardiometabolic risk; ≥0.6 further increased risk (local adult pathway). Interpret BMI and anthropometry with judgement in high muscle mass, pregnancy, oedema, older age or suspected sarcopenia. Fat distribution: truncal with thin limbs (Cushing's, hypothalamic), generalised (dietary), lower body (lipodema — symmetrical painful fat deposits on thighs/lower legs, spares feet — misdiagnosed as lymphoedema). Skin: striae (violaceous + wide = Cushing's; white + narrower = simple obesity), acanthosis nigricans (insulin resistance), hirsutism (PCOS, Cushing's). Thyroid (goitre). BP (hypertension — metabolic syndrome). Oedema (heart failure, nephrotic). Signs of Cushing's: moon face, buffalo hump, proximal weakness, easy bruising; also consider it with wide violaceous striae, unexplained hypokalaemia, osteoporosis, or hypertension or diabetes at a young age. Pulse, JVP and cardiopulmonary status. Signs of androgen excess.

Investigations

Targeted, not routine panels: HbA1c or glucose · TSH (free T4 if indicated) · Renal function + electrolytes · Liver blood tests · Lipid profile · BP · Urine ACR (diabetes, hypertension, CKD or oedema) · NT-proBNP + ECG (if heart failure suspected) · Albumin (if oedema) · FBC (only where clinically indicated) · Cushing's test (one first-line test per local pathway, only with discriminatory features) · Testosterone ± SHBG (suspected PCOS)

The waist circumference measurement is a more important cardiovascular risk indicator than BMI alone and is systematically underused in UK primary care — BMI does not distinguish fat from muscle mass or central from peripheral fat distribution. A patient with BMI 28 (overweight) who has a waist circumference of 105 cm has central adiposity and significantly elevated cardiovascular risk. Conversely, a muscular patient with BMI 28 and waist circumference 88 cm has much lower metabolic risk. The action thresholds: waist circumference above 94 cm in men (above 90 cm in South Asian men — lower threshold because South Asian populations have greater metabolic risk at equivalent waist circumference) or above 80 cm in women increases the risk of metabolic syndrome. Above 102 cm in men and above 88 cm in women substantially increases the risk. NICE NG246 (2025) recommends measuring waist-to-height ratio alongside BMI: 0.4–0.49 healthy central adiposity, 0.5–0.59 increased health risk (advise keeping waist to less than half of height). GPs who measure BMI but not waist circumference at cardiovascular risk assessments are missing clinically important information.

Diagnose

Obesity Classification & Metabolic Syndrome

Done

BMI classification (WHO)

BMI 18.5-24.9 — healthy weight. BMI 25-29.9 — overweight. BMI 30-34.9 — obesity class I. BMI 35-39.9 — obesity class II. BMI ≥40 — obesity class III (severe). Note: NICE NG246 uses lower BMI thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background (overweight: BMI 23–27.4; obesity: BMI ≥27.5). BMI is a screening tool, not a diagnostic tool — clinical judgement and waist circumference are essential co-assessors.

Metabolic syndrome criteria (IDF / AHA-NHLBI 2009)

Central obesity (IDF — mandatory for IDF criteria: WC >94 cm men, >80 cm women — or ethnicity-adjusted) PLUS ≥2 of: TG >1.7 mmol/L · HDL <1.03 (M) or <1.3 (F) mmol/L · BP ≥130/85 mmHg · Fasting glucose ≥5.6 mmol/L. Metabolic syndrome is a risk-stratification construct rather than a diagnosis that changes treatment independently — in primary care focus on BP, HbA1c/glucose, lipids, waist-to-height ratio, cardiovascular risk, fatty liver risk, sleep apnoea and treating each condition. QRISK3 incorporates metabolic syndrome components but does not directly use the composite diagnosis.

NAFLD / metabolic-associated steatotic liver disease (MASLD)

Commonest liver disease in UK — very common, particularly in people with T2DM or obesity. Spectrum: steatosis → NASH/MASH (steatohepatitis) → fibrosis → cirrhosis → HCC. Assessment: ALT/AST (elevated in NASH — ratio ALT:AST >1 in NAFLD; <1 in alcoholic hepatitis), Assess alcohol intake and metabolic risk, then use the local non-invasive fibrosis pathway — usually FIB-4 followed by ELF or transient elastography where indicated (NICE NG49: ELF ≥10.51 = advanced fibrosis → specialist referral). Do not rely on ALT/AST alone to exclude advanced fibrosis. Liver USS (steatosis). FibroScan (vibration-controlled transient elastography — liver stiffness quantification) — increasingly available in primary care and community settings.

NAFLD/MASLD assessment using the FIB-4 score is a guideline-endorsed approach (BSG/BASL 2018; NICE NG49 uses the ELF test) for stratifying liver fibrosis risk in patients with obesity and elevated liver enzymes in primary care — the FIB-4 formula (age × AST / (platelet count × √ALT)) uses readily available blood test results and predicts the likelihood of significant hepatic fibrosis (F2+ fibrosis) with an AUROC of approximately 0.80. The cut-offs: FIB-4 below 1.3 = low risk (negative predictive value approximately 90% for advanced fibrosis — no further investigation needed; repeat FIB-4 every 2–3 years — local NG49/BSG pathway); FIB-4 1.3-2.67 = indeterminate (ELF test or FibroScan); FIB-4 above 2.67 = high risk (proceed per the local pathway — refer if advanced fibrosis, cirrhosis or impaired synthetic function). NICE NG49 (MASLD, formerly NAFLD; 2016, updated July 2026) itself recommends the ELF test to assess for advanced fibrosis; FIB-4 as the first-line primary care step comes from BSG/BASL (2018) and local pathways. GPs should calculate FIB-4 for patients with NAFLD/MASLD risk factors (obesity, T2DM, metabolic syndrome) — the annual review is a convenient prompt — and repeat it every 2–3 years (local NG49/BSG pathway) while it stays low risk. This is a 30-second calculation from existing blood tests and can prevent unnecessary hepatology referrals for low-risk patients while identifying high-risk patients who need specialist input.

Refer

Referral Pathways

Done

999 / Same-day

Acute decompensated heart failure (severe dyspnoea + oedema) · Myxoedema coma (severe hypothyroidism + altered consciousness) · Pulmonary oedema · Severe electrolyte disturbance · Acute kidney injury · Decompensated liver disease

Endocrinology

Abnormal first-line Cushing's test (discuss with endocrinology) · Confirmed endocrine disease after appropriate biochemical assessment · PCOS with severe hyperandrogenism, diagnostic uncertainty or complex metabolic/endocrine disease (refer by fertility needs as appropriate — not all PCOS with obesity) · Insulinoma (episodic hypoglycaemia + weight gain) · Hypothalamic obesity (post-surgical / post-radiotherapy)

Cardiology / Respiratory

Suspected heart failure — NT-proBNP >2000 ng/L specialist assessment + echocardiography within 2 weeks; 400–2000 ng/L within 6 weeks (NICE NG106; local pathway) · Severe OSA requiring CPAP assessment

Nephrology

Suspected nephrotic syndrome (heavy proteinuria + oedema + hypoalbuminaemia) — urgent discussion; same day if severe oedema, acute kidney injury, thrombosis, infection or unstable

Gynaecology (suspected cancer pathway)

Ascites, or a pelvic or abdominal mass not obviously uterine fibroids, in a woman (NICE NG12)

Hepatology

Advanced fibrosis on the local non-invasive pathway (e.g. ELF ≥10.51 or elastography) · Cirrhosis or impaired synthetic function (low albumin, elevated INR, thrombocytopenia) · Portal hypertension · Diagnostic uncertainty — not FIB-4 alone

Specialist weight management / bariatric surgery

Comprehensive specialist assessment if BMI ≥40, or 35–39.9 with a significant condition likely to improve with weight loss (e.g. T2DM, hypertension, OSA), and the person agrees to long-term follow-up; lower BMI thresholds for specified ethnic groups. Recent-onset T2DM: expedited assessment at BMI ≥35, and may be considered at 30–34.9. NICE NG246 has moved away from a rigid tiered model — do not require failure of Tier 1–2 in every case or delay referral with repeated lifestyle attempts. Eligibility also reflects clinical complexity and local commissioning.

The bariatric surgery referral pathway in the UK has been expanded by NICE NG246 — notably, the accelerated pathway allows direct referral for bariatric surgery consideration in patients with BMI ≥35 and recently diagnosed T2DM (diagnosed within 10 years), bypassing the requirement to first complete Tier 2-3 weight management programmes. This is because the SOS trial, STAMPEDE trial, and multiple other RCTs demonstrate that bariatric surgery achieves T2DM remission in approximately 30-70% of patients (depending on procedure and duration of diabetes), which is substantially better than any medical treatment. The DiRECT trial also shows that intensive dietary intervention (800 kcal/day VLCD for 12 weeks) achieves T2DM remission in approximately 46% at 12 months — this can be offered through NHS Tier 2 programmes before surgical referral for motivated patients. GPs should be aware that bariatric surgery in eligible patients reduces: T2DM burden, cardiovascular events, sleep apnoea, and all-cause mortality — it is not a cosmetic intervention.

Treat

Weight Management — Pharmacological Interventions

Done

Step 1 Lifestyle interventionAll patients: dietary modification (500-600 kcal/day deficit from current intake — do not use very low calorie diets without supervision) + physical activity (150 min/week moderate aerobic + muscle-strengthening 2x/week) + behavioural change (food diary, self-weighing, structured goals). NHS Tier 2 referral: community weight management programme (12-week minimum). Brief interventions in primary care: "Making Every Contact Count" (MECC). Target: 5-10% weight loss at 6-12 months (clinically meaningful — reduces CVD risk, T2DM risk, OSA, joint pain).

Step 2 Anti-obesity medicationTirzepatide (Mounjaro) — GIP/GLP-1 receptor agonist. NICE TA1026: alongside a reduced-calorie diet and increased physical activity, initial BMI ≥35 kg/m² plus at least one weight-related comorbidity; thresholds usually 2.5 kg/m² lower for South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds. May be prescribed in primary care or a specialist service — route and eligibility are subject to NHS England and local ICB/local commissioning; confirm the current local pathway before prescribing. Semaglutide 2.4 mg SC weekly (Wegovy — not Ozempic) — GLP-1 receptor agonist. NICE TA875 (2023): at least 1 weight-related comorbidity and BMI ≥35 (or 30–34.9 and meeting specialist-referral criteria), within a specialist weight management service with dietary and physical-activity support, usually up to 2 years; consider stopping if <5% of initial body weight lost after 6 months. More restricted than tirzepatide in the local formulary. STEP 1 trial mean loss (14.9% vs 2.4% placebo at 68 weeks) is a trial average, not an individual target or guaranteed response. Dose titration: 0.25 mg/week x4, 0.5 mg/week x4, 1 mg/week x4, 1.7 mg/week x4, then 2.4 mg/week maintenance if tolerated (use current product information and local protocol). Safety (semaglutide/tirzepatide): nausea, vomiting, diarrhoea, constipation; dehydration and acute kidney injury risk, particularly during dose escalation; gallbladder disease; acute pancreatitis — same-day assessment for sudden severe abdominal pain, stop if suspected, do not restart if confirmed; delayed gastric emptying (peri-anaesthetic aspiration risk); review insulin and sulfonylurea doses (hypoglycaemia); do not combine tirzepatide with another GLP-1 receptor agonist or a DPP-4 inhibitor; sudden visual loss on semaglutide → same-day eye casualty or A&E (MHRA: very rare NAION). Contraception and pregnancy: tirzepatide can reduce oral contraceptive effectiveness during initiation and for 4 weeks after each dose escalation — use a non-oral method or add a barrier method; stop semaglutide at least 2 months and tirzepatide at least 1 month before planned pregnancy; do not use in pregnancy or breastfeeding. US labelling (international) contraindicates it with a personal/family history of medullary thyroid carcinoma or MEN2.

Step 2 (alternative) OrlistatOrlistat 120 mg TDS (with each main meal containing fat) — pancreatic lipase inhibitor; reduces fat absorption by approximately 30%. Weight loss: approximately 3-4 kg greater than placebo at 1 year. Available OTC (alli 60 mg) or on prescription. Side effects: steatorrhoea, oily stools, faecal urgency/incontinence (reduced by low-fat diet). Contraindicated: malabsorption syndrome. Vitamin ADEK supplementation if on orlistat long-term. NICE NG246: orlistat only if lifestyle changes have been initiated + patient is committed to continuing.

Step 3 Bariatric surgeryProcedures include Roux-en-Y gastric bypass, sleeve gastrectomy and adjustable gastric band (most reversible); outcomes vary by procedure, population, follow-up and definition of weight loss. All require: comprehensive specialist assessment, psychological assessment, multidisciplinary team, lifelong follow-up. Complications: dumping syndrome (bypass), nutritional deficiencies (B12, iron, calcium, vitamin D — mandatory supplementation lifelong), anastomotic leak.

Semaglutide 2.4 mg (Wegovy) represents the most significant advance in pharmacological obesity treatment in decades — the STEP 1 trial demonstrated 14.9% mean weight loss versus 2.4% for placebo over 68 weeks in adults with BMI ≥30 (or ≥27 with comorbidity), without diabetes. The SELECT trial (2023, NEJM) showed that semaglutide 2.4 mg reduces major adverse cardiovascular events (MACE — myocardial infarction, stroke, cardiovascular death) by 20% in patients with overweight/obesity and established cardiovascular disease, independently of weight loss. This cardiovascular outcome data has transformed the framing of obesity pharmacotherapy from 'cosmetic' to 'life-saving' — semaglutide is now indicated both for weight reduction and for cardiovascular risk reduction in appropriate patients. NICE TA875 approved semaglutide 2.4 mg for weight management in England for patients with at least one weight-related comorbidity and BMI ≥35 (or 30–34.9 meeting NG246 criteria for specialist referral), within a specialist weight management service. GPs cannot currently initiate Wegovy under TA875 — but NICE TA1026 (tirzepatide) is being rolled out in primary care in prioritised cohorts from 23 June 2025 (first cohort: BMI ≥40 with at least four of five qualifying comorbidities, per NHS England interim commissioning guidance).

Treat

Managing Drug-Induced Weight Gain & Endocrine Causes

Done

Antipsychotic-induced weight gain

Metabolic monitoring: weight, BMI, WC, BP, fasting glucose, fasting lipids — at baseline, weight weekly for 6 weeks, then at 12 weeks, 1 year, then annually (NICE CG178). If significant weight gain: discuss with the psychiatric team — do not switch antipsychotics from primary care. Switching can destabilise mental health and lower-weight-gain options (e.g. aripiprazole, lurasidone) are not universally suitable; olanzapine and clozapine carry the most weight gain but clozapine is sometimes the only effective option. Metformin may be considered for antipsychotic-associated weight gain, following local psychiatric/diabetes guidance, with renal function and gastrointestinal tolerability considered.

Corticosteroid-induced weight gain

Review indication and dose: can steroids be tapered or stopped? Minimum effective dose principle. Switch to inhaled/topical where possible (lower systemic absorption). If long-term systemic steroids unavoidable: monitor metabolic parameters (BP, HbA1c, lipids, BMI) annually. Steroid-sparing agents (azathioprine, methotrexate, mycophenolate) can reduce steroid requirements. Weight gain from steroids: primarily truncal (Cushingoid) + fluid retention — sodium restriction + dietary modification.

Hypothyroidism

Levothyroxine: correct dose restores euthyroid state — most (but not all) hypothyroidism-related weight gain resolves. Target TSH: within the reference range (NICE NG145); do not escalate levothyroxine for persistent symptoms alone if TSH is within range. Weight loss on levothyroxine is usually modest (mainly the fluid component) — patients with pre-existing obesity will not achieve significant weight loss from levothyroxine alone. Combination T3/T4 is not a weight-management option.

Oedema and fluid management

Treat oedema according to the underlying cause. Assess renal function, electrolytes, albumin, liver tests, urine ACR/PCR, ECG and natriuretic peptide where appropriate. Avoid empiric high-dose diuretics in primary care unless there is an established diagnosis and a documented monitoring plan. Heart failure: follow the current heart-failure pathway (treatment depends on ejection fraction, renal function, potassium, BP and current medicines). Nephrotic syndrome: nephrology-led. Ascites: specialist-led diuretic titration with biochemical monitoring. Venous oedema/lymphoedema: compression hosiery + limb elevation + manual lymphatic drainage.

Next steps: see Obesity · Type 2 diabetes · Fatty liver (MASLD) · Hypothyroidism · Snoring and sleep apnoea

Metformin for antipsychotic-induced weight gain is an evidence-based intervention that is underused in UK primary care — a meta-analysis (Zheng 2015) showed that metformin 500-1000 mg BD in patients on antipsychotics reduced body weight by approximately 3 kg and improved insulin sensitivity compared to placebo, without significant adverse effects. The mechanism: metformin reduces hepatic glucose output and improves insulin sensitivity, partially counteracting the insulin-resistance-promoting effects of olanzapine and clozapine. NICE CG178 (psychosis and schizophrenia in adults) does not yet make a recommendation on metformin (its 2023 surveillance found about 3 kg less weight gain with metformin and planned an update on add-on therapies); in specialist practice metformin can be considered for patients with antipsychotic-induced weight gain who have not responded to lifestyle interventions alone. Any metformin use for this indication should follow local psychiatric/diabetes guidance, with renal function and gastrointestinal tolerability considered.

Lifestyle

Behaviour Change, Diet & Physical Activity

Done

Evidence-based dietary approaches for weight loss No single diet is superior — adherence is the primary determinant of success. Approaches with evidence: (1) Energy restriction (500-600 kcal/day deficit from current intake) — any method; (2) Very low calorie diet (VLCD — 800 kcal/day) for structured 12-week programmes (DiRECT trial: 46% T2DM remission at 12 months); (3) Low-carbohydrate diet (total carbohydrate <130g/day) — effective for weight loss and glucose control in T2DM (SACN reviewed evidence); (4) Mediterranean diet — sustainable, cardiovascular benefit, modest weight loss. Avoid: promoting very low calorie diets without supervision (risk of nutrient deficiency, gallstones, electrolyte imbalance).

Physical activity prescription NICE NG246: 150 min/week moderate-intensity aerobic exercise (brisk walking, cycling, swimming) + muscle-strengthening activities 2 days/week. Start low and go slow: 10 min walks initially for very sedentary patients; build up gradually. Exercise does not produce large weight loss alone (considerably less than dietary restriction) but provides critical benefits independent of weight loss: cardiovascular risk reduction, insulin sensitivity, muscle preservation, mental health. Exercise is more important for weight maintenance than initial weight loss.

Sleep optimisation for weight management Short sleep may increase ghrelin (appetite-stimulating) and reduce leptin (satiety hormone), promoting overeating. Treat OSA (CPAP): reduces ghrelin, improves insulin sensitivity, reduces metabolic syndrome features. Sleep hygiene counselling: consistent wake time, dark/cool room, no screens 1h before bed, no caffeine after 2pm. PHQ-9 screen: depression-related sleep disruption and emotional eating.

Reducing ultra-processed food intake Ultra-processed foods (UPF — NOVA classification 4) — industrially produced foods with many additives — make up a large share of calories in the average UK diet. Multiple RCTs and cohort studies show UPF consumption is independently associated with obesity, T2DM, CVD, and cancer. Practical advice: cook from raw ingredients more frequently; read food labels; limit: crisps, biscuits, ready meals, fast food, sweetened drinks, processed meats; choose: whole foods, fresh produce, legumes, nuts, home-prepared meals.

Alcohol and weight Alcohol provides 7 kcal/g — a standard glass of wine (175 ml, 12%) = approximately 150 kcal (equivalent to a KitKat). Heavy drinking can add substantial calories each week. Alcohol also stimulates appetite (aperitif effect via hypothalamic mechanisms) and reduces inhibition around food choices. For patients with obesity + significant alcohol intake: quantify with AUDIT-C at every review. Brief advice on alcohol reduction. FRAMES brief intervention. Target: below 14 units/week.

Emotional eating and behavioural support Emotional eating (eating in response to negative emotions rather than hunger) is common among people seeking weight-management treatment. CBT-based approaches: food and mood diary, identifying emotional eating triggers, developing non-food coping strategies, mindful eating. NHS Talking Therapies referral for emotional eating with anxiety or depression. Specialist eating disorder services if binge eating disorder (BED) suspected (recurrent uncontrolled eating episodes without compensatory behaviours). Ask about binge-eating symptoms at assessment.

Commercial weight management programmes NHS referral to commercial weight management programmes: Weight Watchers (WW), Slimming World — NHS voucher schemes available in some areas. These programmes provide structured group support, accountability, and evidence-based dietary advice. More effective than brief GP advice alone. Particularly effective when: patient motivation is high, regular weigh-ins, group social support. Tier 2 NHS programmes (community dietitian-led): available in most areas via GP referral.

Weight stigma and compassionate care Weight stigma (negative attitudes toward people with obesity) in healthcare settings reduces treatment engagement, increases psychological distress, and worsens health outcomes. GPs should: use patient-centred language ("person with obesity" not "obese person"), ask permission before discussing weight, acknowledge the complexity of obesity (genetics, environment, biology — not just choice), avoid attributing all symptoms to weight. HAES (Health at Every Size) principles: focus on healthy behaviours rather than weight as the sole measure of success. Motivational interviewing techniques improve engagement.

The VLCD (very low calorie diet, 800 kcal/day) approach for T2DM remission, tested in the DiRECT trial (Lean et al., NEJM/Lancet 2018), represents one of the most important recent paradigm shifts in obesity and diabetes management — the trial showed that intensive dietary intervention (Counterweight-Plus total diet replacement programme, 825-853 kcal/day for 12 weeks, then food reintroduction and structured support) achieved T2DM remission (HbA1c <48 mmol/mol off all antidiabetic medications) in 46% of participants at 12 months and 36% at 24 months, compared to 4% in the standard care group. Weight loss of 10-15 kg was the critical driver of remission. This is substantially better than any pharmacological treatment for T2DM remission (metformin and SGLT2 inhibitors do not cause remission — they control glucose). NHS England has commissioned the NHS Low Calorie Diet Programme, which delivers VLCD intervention to patients with T2DM diagnosed within 6 years and BMI ≥27 (≥25 in South Asian populations). GPs should refer eligible patients to this programme — it is the single most effective intervention for T2DM remission in primary care.

Safety

Follow-Up, Monitoring & Targets

Done

Weight management review schedule

Initial: monthly for first 3 months (weight, BMI, WC, BP, HbA1c, lipids, side effects of medication). Orlistat: review at 3 months — continue beyond 3 months only if at least 5% of initial body weight has been lost (NICE NG246). Semaglutide/tirzepatide: formal review at 6 months — consider stopping if <5% of initial body weight lost (NICE). Annual: metabolic screen (BP, HbA1c, lipids, LFTs), QRISK3 recalculation, STOP-BANG for OSA, fibrosis assessment per the local NAFLD pathway.

Weight loss targets and expectations

Clinically meaningful weight loss: 5-10% initial body weight. At 5% loss: significant reduction in T2DM risk, improved BP, improved lipids. At 10% loss: triglycerides fall, HDL increases, insulin sensitivity improves significantly, OSA improves. T2DM remission: 15% weight loss is associated with highest remission rates. Realistic rate: 0.5-1 kg/week with lifestyle + medication.

Drug-induced weight gain monitoring

Antipsychotics: metabolic monitoring at baseline, 12 weeks, 1 year, then annually (NICE CG178). Corticosteroids: HbA1c + BP annually, DEXA for bone density, monitor weight. Insulin: quarterly weight at diabetic reviews. Discuss weight-neutral alternatives with the prescriber where clinically appropriate (antipsychotic switches are psychiatry-led).

Referral review

Refer for specialist assessment when NICE NG246 criteria are met (BMI ≥40, or 35–39.9 with significant comorbidity; lower thresholds for specified ethnic groups) — do not delay by repeated lifestyle attempts. Waits for bariatric surgery can be long — maintain lifestyle work during the waiting period.

999 / Same-day

Acute heart failure (severe dyspnoea at rest + oedema) · Myxoedema coma (confusion + bradycardia + severe hypothyroidism) · Pulmonary oedema · Acute kidney injury · Severe electrolyte disturbance · Decompensated liver disease

Urgent / specialist

Urgent medical assessment: new oedema with heavy proteinuria/hypoalbuminaemia (urgent nephrology discussion; same day if severe oedema, AKI, thrombosis, infection or unstable), suspected heart failure (NT-proBNP >2000 ng/L: echo within 2 weeks; 400–2000 ng/L: within 6 weeks), ascites or a pelvic/abdominal mass (suspected cancer pathway, NG12), rapidly progressive endocrine features · Routine endocrinology: confirmed endocrine disease after appropriate biochemical assessment · Hepatology: advanced fibrosis, cirrhosis or impaired synthetic function (not FIB-4 alone) · Specialist weight management: per BMI, comorbidity, ethnicity, clinical complexity and local commissioning

Safety-net — say it

999: "Call 999 if you are breathless at rest or cannot lie flat, cough up pink frothy spit, or become very drowsy, confused or very cold." Same day: "Contact us today if the swelling in your legs or tummy is quickly getting worse, you pass much less urine, or you have frothy urine with swelling. On a weight-loss injection: severe tummy pain that does not settle — stop the injection and get seen today (A&E); sudden loss of vision in one eye — eye casualty or A&E today; vomiting so you cannot keep fluids down — contact us today." Within 2 weeks: "Book to see us if your tummy is bloated or swollen most days, you feel full quickly, or you notice new purple stretch marks, easy bruising or weak thigh muscles." Remote or OOH: breathlessness, new swelling or drowsiness reported remotely → same-day face-to-face (999 if breathless at rest).

The QRISK3 recalculation at annual weight management review is a tangible motivator for patients that GPs often overlook — showing a patient their QRISK3 cardiovascular risk score before and after a 5-10% weight loss demonstrates the direct health benefit of their effort in quantitative terms. Recalculating risk after weight loss can show a meaningful reduction that may translate into reduced likelihood of needing statins or antihypertensives, and a tangible reward for the patient's effort. Similarly, showing an HbA1c reduction can be a powerful motivator. GPs should incorporate before/after metabolic data comparisons into every annual weight management review — framing weight loss not as an aesthetic goal but as a directly measurable health improvement with quantified outcomes.