Obesity/overweight in adults - clinical fact sheet and MCQ

Overview

Obesity is a chronic, relapsing condition marked by excessive body fat accumulation that adversely affects health. In Australia, 31.7% of adults are living with obesity and a further 34.0% are overweight. Overweight and obesity significantly elevate the risk of numerous chronic conditions, including cardiovascular disease, type 2 diabetes, metabolic dysfunction-associated steatotic liver disease (MASLD), several cancers (eg colorectal, thyroid, and liver), osteoarthritis, infertility, and depression.

Obesity is influenced by biological, psychosocial, environmental, and structural factors. It is not solely a result of individual behaviours. Treatment must reflect this complexity, and should avoid simplistic, weight-centric models. A person-centred, holistic, and inclusive approach is central to effective care.

Diagnosis of obesity and overweight

Assessment must consider the functional, metabolic, and psychological impacts of excess adiposity.

Obesity is diagnosed using the following key diagnostic measures:

• BMI categories (adults):

• overweight: 25.0–29.9 kg/m²

• obesity (class I–III): ≥30.0 kg/m²

• Note that classification of obesity classes are dependent on ethnicity (see table below)

Classification of BMI from the Australian Government clinical practice guidelines, where population specific BMI relates to those of Asian, Middle Eastern, Black African, or African Caribbean background. 

• waist circumference: assesses central adiposity and should complement BMI

• increased risk: >80 cm for women; > 94cm for men

• greatly increased risk: >88 cm for women; >102 cm for men

• Edmonton Obesity Staging System considers medical, mental, and functional health to guide treatment intensity

• pre-exercise screening tools: use Exercise & Sports Science Australia (ESSA) tools (eg adult pre-exercise screening system) prior to initiating physical activity programs

Additional considerations during assessment:

• take a detailed history (weight trajectory, diet, activity, sleep, psychosocial context)

• screen for disordered eating, especially binge eating disorder

• consider comorbid conditions and contributing medications

• use appropriately sized equipment and maintain patient dignity (eg weigh in private)

• explore the individual’s lived experience, goals, and barriers to engagement

Management of obesity and overweight in primary practice

Management is guided by the 5As framework:

5As framework from the Australian Government clinical practice guidelines.

 A respectful, empathetic, and collaborative approach is crucial. There is no one-size-fits-all pathway. Individual preferences, health status, and life context should determine the management plan.

Note that the approach to managing obesity in older adults (> 65 years) may differ to that of younger adults, as there is no consensus on target BMI in this cohort. Loss of height, muscle mass, and increase in abdominal obesity are not considered in BMI calculations. The primary goal in the older age group is to optimise physical function and reduce obesity-related complications.

1. Behavioural interventions

• Nutrition: evidence supports both dietary patterns without fixed energy goals (eg DASH, Mediterranean) and those with energy restriction (eg low energy diets, intermittent fasting). These should be tailored in partnership with the patient to accommodate preferences and contraindications for certain diets.

• Consider initiating nutritional intervention with a specific daily energy intake target, followed by ongoing dietary management with no specific daily energy intake goal

• Additional dietary approaches include commercially-available meal replacements and very low energy diets, or one adhering to the Australian Guide for Healthy Eating

• Physical activity: physical activity and sedentary behaviour have separate effects on health. Reducing sedentary behaviour is important. Physical activity interventions evaluated to support weight loss and subsequent maintenance typically comprise regular aerobic or strengthening activities alone, or in combination.  

• Aim to meet the national physical activity recommendations while minimising the risk of injury; may need a gradual approach.

• Sleep: optimising sleep duration and quality may assist in weight management in combination with nutrition and exercise interventions.

• Psychological support: cognitive behavioural therapy and motivational interviewing alongside nutrition and exercise interventions can support adherence and address emotional factors. Family-based interventions may be indicated. 

2. Pharmacological interventions

Adults with a BMI >30 or those with BMI >27 with weight-related comorbidities should be considered for pharmacological intervention alongside behavioural modifications. A collaborative approach with the patient includes discussion about benefits and risks, side effects, and costs.

The Therapeutic Goods Administration (TGA) has approved the following for weight management:

• semaglutide

• liraglutide

• phentermine

• tirzepatide

• orlistat

• naltrexone/bupropion

However, it is recommended to consult the TGA website regularly for updates in this area.

Monitor for side effects (particularly GI symptoms, headache, insomnia, and palpitations; can often be minimised by a gradual increase in dose), drug interactions, and long-term safety. Regular follow-up is essential. None of the above are PBS-funded; cost can be a barrier. A table summarising these medications and their details can be found in appendix D (pg 72) of the Australian Government Department of Health and Aged Care draft guidelines.

3. Surgical interventions for obesity and overweight

Metabolic and bariatric surgery may be appropriate for individuals with:

• class I obesity with weight-related comorbidities inadequately managed with non-surgical intervention

• class II obesity or higher regardless of weight-related comorbidities

Common procedures include sleeve gastrectomy and gastric bypass. Surgery must be delivered as part of a multidisciplinary care plan with long-term follow-up, nutritional monitoring, and psychological support. 

Note: MBS rebate is available only when BMI ≥40, or if BMI ≥35 with other significant co-morbidities. 

4. When to refer

GPs should consider referral to specialist weight management services when:

• there is severe or complex obesity

• multimodal treatment is required (eg psychology, pharmacotherapy)

• there are significant comorbidities

• the patient is a candidate for pharmacotherapy or bariatric surgery

• eating disorders are suspected or confirmed

Special considerations for certain at-risk groups, eg Aboriginal and Torres Strait Islanders, those with a disability, can be found in detail in the Australian Government clinical summary guidelines.

References

1. Australian Government Department of Health and Aged Care. Clinical Practice Guidelines for the Management of Overweight and Obesity for Adults, Adolescents and Children in Australia. Draft Guidelines, November 2024. (last accessed May 2025).
2. Markovic T, Proietto J, Dixon J, et al. The Australian Obesity Management Algorithm: A simple tool to guide the management of obesity in primary care. Obesity Research & Clinical Practice. 2022;16(5):353-363.

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