Obesity

Health consequences of obesity

• Abdominal (“apple”) fat distribution is a greater cardiometabolic hazard than gluteofemoral (“pear”) fat distribution.
• Waist–hip ratio >1.0 (men) or >0.9 (women) carries a significantly greater risk of diabetes, stroke, coronary artery disease and early death than equally obese people with lower ratios.
• Cardiovascular: increased mortality (stroke, ischaemic heart disease), hypertension, varicose veins.
• Metabolic: dyslipidaemia, type 2 diabetes, insulin resistance, hyperuricaemia/gout, infertility, PCOS.
• Mechanical: osteoarthritis, obstructive sleep apnoea, restrictive pulmonary disease, spinal dysfunction, low back pain, urinary incontinence.
• Other: hiatus hernia/GORD, gallbladder disease, fatty liver, several cancers, kidney disease (check microalbuminuria), excessive daytime sleepiness, erectile dysfunction/subfertility, psychological problems/depression/anxiety.
• Obesity is estimated to be responsible for a substantial proportion of type 2 diabetes, ischaemic heart disease and hypertension in Western populations.

Factors predisposing to primary obesity: family history, female sex, physical inactivity, emotional deprivation/depression, lower socioeconomic status, problem drinking, smoking cessation, and some prescribed drugs (e.g. tricyclic antidepressants).

Metabolic syndrome

Central obesity by waist circumference — >102 cm (men), >88 cm (women) in a European population — plus any 2 or more of:

• ↑ triglycerides >1.7 mmol/L
• ↓ HDL cholesterol <1.0 mmol/L (men) / <1.3 mmol/L (women)
• fasting glucose ≥5.5 mmol/L
• blood pressure ≥130/85 mmHg

The cluster carries an increased risk of type 2 diabetes and atherosclerotic vascular disease, and warrants aggressive risk-factor management (see Type 2 Diabetes Management).

Assessment

The HNE HealthPathways approach frames assessment around health, not just a weight number, using the “5 A’s”: Ask permission to discuss weight and its health impacts; Assess the patient’s readiness/motivation, social factors, weight history, food habits and nutrient intake, physical activity level, and barriers to change; Advise; Agree on goals; Assist.

Also identify risk factors and comorbidities — including mental health conditions and eating disorders — and consider medical conditions/medications that affect weight. Note that some patients prefer a “Health at Every Size” (HAES) approach, focusing on lifestyle-goal progress rather than the number on the scale; this should be respected where expressed.

Baseline measurements: height, weight, waist circumference, BMI.

Case-by-case investigations: baseline U&E/LFT; TFT if an underlying cause is suspected; iron studies, B12, folate, trace elements and vitamin D if a nutritional deficiency is suspected; and screening for diabetes, hyperlipidaemia or obstructive sleep apnoea where indicated.

Management

Treatment centres on four major interventions: reduced energy intake, improved diet composition, increased physical activity, and behavioural therapy — now supplemented, for eligible patients, by injectable pharmacotherapy (below).

Goals: stop further weight gain; lose 5–10% of initial body weight; improve activity levels. HNE HealthPathways frames the treatment goal more broadly as improved health, not weight loss as an end in itself, for patients at every BMI.

A doctor–patient strategy

1. Promote realistic goals — lose weight at roughly the rate it was gained (e.g. 5–10 kg/year); reinforce the energy-balance principle (energy in = energy out + energy stored).
2. Dietary advice — realistic substitutions (e.g. skim for whole milk, wholemeal for white bread, fruit/vegetables for biscuits/cakes); reduce fat to <30% of total calorie intake; eating one-third less than usual and avoiding second helpings/“picking” is a simple, effective starting strategy for overweight and grade I obesity.
3. Counselling — supportive, non-judgemental; a food/exercise/behaviour diary helps.
4. Review — the most important part of any weight-loss programme, for motivation and progress assessment. HNE HealthPathways specifies a concrete schedule: every 2 weeks for the first 3 months, a medical review at 3 months, and ongoing support for at least 12 months (consider recall/reminder systems). At each review: monitor any medication, monitor cardiovascular/diabetes risk, provide education and support, and identify small amounts of weight regain early (e.g. agree in advance on a regain threshold that triggers seeking advice). Re-evaluate the whole management strategy at 3 months if there has been <1% body weight loss, no change in waist circumference, or small regain (e.g. ~3 kg). Once goals are met (e.g. 5% body weight lost, target blood pressure reached), move to long-term weight-management planning.

Practical lifestyle advice

• Brisk 20–30 minute daily walk is the most practical exercise; other activities (tennis, swimming, golf, cycling) are a bonus.
• Favour natural, high-fibre, low-GI foods; wholemeal bread and cereals; lean meat/poultry (skin removed)/fish; plenty of vegetables and fruit.
• Limit sugar, fried and high-fat foods, sugary drinks and alcohol; drink copious water (≥2 L/day).
• Sensible, gradual goals (6–12 month plan) rather than crash dieting; exercise plus diet, not dieting alone.
• Eat slowly; avoid non-hungry eating and seconds; a small weekly treat is fine.

Referral

HNE HealthPathways recommends a multidisciplinary approach: dietitian (shopping, diet planning, goal setting), psychologist (goal setting, behavioural/body-image concerns, assessment for underlying disordered eating), exercise physiology, physiotherapy, endocrinology (if endocrine dysfunction suspected), and bariatric surgery (if an appropriate candidate). Refer any suspected eating disorder for specialised assessment first. In NSW, the Get Healthy Service supports behavioural change; eligible First Nations patients can be referred to the Integrated Team Care (ITC) program.

Pharmacological management

GLP-1 receptor agonists (liraglutide, semaglutide) and the dual GIP/GLP-1 receptor agonist tirzepatide are now the mainstay of injectable pharmacotherapy for weight management, replacing the older agents this note originally listed (orlistat, phentermine, fluoxetine/SSRIs). They mimic the incretin hormones GLP-1 and GIP, acting on hypothalamic/mesolimbic appetite centres to increase satiety and reduce food enjoyment, slow gastric emptying, and stimulate pancreatic insulin release/reduce glucagon.

TGA-approved indications (as an adjunct to a reduced-energy diet and increased physical activity): adults with obesity (BMI ≥30 kg/m²); adolescents with obesity (semaglutide only); and adults who are overweight (BMI 27–<30 kg/m²) with at least one weight-related comorbidity. Note that semaglutide as Ozempic is not approved for weight management (only for type 2 diabetes and slowing kidney function decline in T2DM) — only semaglutide as Wegovy carries the weight-management and cardiovascular-risk-reduction indications. Tirzepatide (Mounjaro) is also approved for type 2 diabetes and moderate-to-severe obstructive sleep apnoea in adults with overweight/obesity.

Comparative efficacy (mean weight loss at trial end vs placebo, lifestyle intervention in both arms): liraglutide 3.0 mg daily ~8.0% vs 2.6% (SCALE, 56 weeks); semaglutide 2.4 mg weekly ~14.9% vs 2.4% (STEP 1, 68 weeks); tirzepatide 15 mg weekly ~20.9% vs 3.1% (SURMOUNT-1, 72 weeks). Tirzepatide produced significantly greater weight loss than semaglutide in a head-to-head trial (SURMOUNT-5: 20.2% vs 13.7% at 72 weeks).

Adverse effects: predominantly gastrointestinal (nausea, bloating, constipation, diarrhoea; rarely gastroparesis) — 6–13.5% of trial participants discontinued treatment, mainly for GI, biliary, ocular or mental-health effects. Increased risk of gallstones and pancreatitis. Thyroid/pancreatic cancer signals have been raised but current evidence is reassuring (though these cancers are rare enough that a small true risk increase could take years to detect). A nonarteritic anterior ischaemic optic neuropathy (NAION) signal has been observed and needs further study. Mental health monitoring is important: these drugs can alter a patient’s relationship with food and pleasure, which can mask other causes of appetite loss (infection, cancer, depression, eating disorder) and may exacerbate depression/suicidality in some patients — an active area of research. Misuse by people without obesity (particularly those with eating disorders) is a recognised risk; asking about a patient’s highest-ever weight can help surface this. Because gastric emptying is slowed, standard pre-procedure fasting may be insufficient — a 24-hour clear fluid diet in addition to standard 6-hour fasting is recommended before general anaesthaesia.

Prescribing practicalities: start at the lowest dose and titrate slowly as tolerated; individualise dose to efficacy and tolerability (a lower than manufacturer-recommended dose may be sufficient); manage mild GI adverse effects with smaller/lower-fat meals and good hydration before reducing dose or stopping; stop 1 month (liraglutide) or 2 months (semaglutide, tirzepatide) before a planned pregnancy. For tirzepatide specifically, initially 2.5 mg once a week for 4 weeks then increase to 5 mg once a week; if required, at intervals of at least 4 weeks, increase by increments of 2.5 mg once a week up to a maximum of 15 mg once a week. Avoid combining tirzepatide with a DPP-4 inhibitor, since they have similar modes of action and the combination is unlikely to provide additional clinical benefit. Additional precautions include gall bladder disease (increased risk of cholecystectomy), a history of pancreatitis (used with caution — excluded from trials), and diabetic retinopathy (may worsen); if using an oral contraceptive, its effectiveness may be reduced in the 4 weeks after starting or increasing the dose of tirzepatide, so add a barrier method during this time or use a non-oral contraceptive method.

Weight regain after stopping is the norm — these drugs do not cure obesity. In the STEP 1 extension study, the proportion of participants with ≥5% weight loss fell from 86.4% to 48.2% twelve months after stopping semaglutide (vs 31.5% to 22.6% with placebo). An unreviewed systematic-review preprint estimated regain plateaus at around 75% of the weight lost on treatment, with a disproportionate share regained as fat rather than muscle — patients should be supported to build/maintain muscle mass both during and after treatment. Sustained weight reduction generally requires long-term use alongside ongoing multidisciplinary, behavioural and lifestyle support.

Access: as of the article date, none of these drugs are PBS-listed for weight management specifically (PBS-subsidised for type 2 diabetes only, aside from the one CVD-risk exception below) — private cost can run to hundreds of dollars a month, a substantial barrier for many patients. That exception: semaglutide (Wegovy) has a PBAC-recommended listing specifically for patients with established cardiovascular disease.

Orlistat, phentermine and fluoxetine/SSRIs (the agents originally listed in this note) remain available but are now considered older, less effective options superseded by the incretin-based injectables above; the same caution about drugs not having a continuing effect once stopped applies to all of them.

Surgery (bariatric surgery)

Surgery remains the most effective treatment for obesity, though pharmacotherapy is now frequently used first-line or alongside surgery rather than only after it fails. It carries risks such as malabsorption and nutritional deficiency. Recommended for BMI >40, or >35 with a severe comorbidity (e.g. poorly controlled diabetes, severe OSA), after an adequate trial of behavioural and pharmacological measures. In Australia, sleeve gastrectomy is now the most common bariatric operation, followed by gastric bypass surgery (Roux-en-Y or one-anastomosis); sleeve gastrectomy is primarily restrictive, while gastric bypass combines restriction with malabsorption. Adjustable gastric banding is also an option. Common chronic conditions that may improve with the resulting weight loss include hypertension, diabetes and osteoarthritis pain, so drug doses (e.g. antihypertensives, insulin/sulfonylureas, analgesia) often need downward adjustment over time. Lifelong vitamin and mineral supplementation is required post-operatively — typically a multivitamin plus calcium, vitamin D, iron and vitamin B12 — with periodic laboratory surveillance for deficiencies, since routine supplementation alone does not guarantee prevention (individual variation in absorption, requirements, surgery type and adherence all play a part); a bariatric-trained dietitian should be part of the ongoing management team. Women should avoid pregnancy for at least 12–18 months after surgery, and since fertility can improve dramatically with weight loss (especially in PCOS), effective contraception becomes more, not less, important in this window.