• Calculate the person's body mass index (BMI) by dividing their weight in kilograms by the square of their height in metres. An online calculator is available at www.nhs.uk.
• The National Institute for Health and Clinical Excellence classify adults as overweight or obese using their BMI:
• Overweight — BMI of 25–29.9 kg/m².
• Obesity l — BMI of 30–34.9 kg/m².
• Obesity ll — BMI of 35–39.9 kg/m².
• Obesity lll — BMI of greater than or equal to 40 kg/m².
• Interpret BMI with caution in very muscular adults, as it is a less accurate measure of adiposity in this group.

• Assess:
• Underlying causes and comorbidities.
• Risk of developing complications of obesity.
• Lifestyle in terms of diet and exercise.
• The potential health benefits of weight loss to the person.
• The person's feelings about being overweight.
• The person's willingness and motivation to try to lose weight.

In depth

• Take a history to include:
• Medical history — medical conditions that can contribute to overweight and obesity, or complications that may arise as a result of excess weight.
• Family history — overweight and obesity, and comorbidities.
• Drug history — medication that might cause weight gain.
• Social history — lifestyle, diet, exercise, alcohol and smoking, work and leisure activities.
• Check blood pressure using a large arm cuff.
• Check blood glucose and lipid profile, preferably on a fasting sample.
• Consider other tests if appropriate on the basis of assessment findings (e.g. liver function tests, thyroid function tests).

In depth

• Calculate the person's body mass index (BMI) if this has not already been done.
• Measure waist circumference in people with a BMI less than 35 kg/m².
• Using this information, assess whether the person is at increased risk of cardiovascular and metabolic complications. Note: Asian people may be at higher risk, and older people at lower risk, for a certain BMI compared with the general population.
• Ask about family history of diabetes (including gestational diabetes) and coronary heart disease.

In depth

• Determine if the person wants to lose weight at the present time by asking about concerns regarding weight, importance of losing weight, and quality of life issues.
• Explore barriers to lifestyle change (e.g. cost and availability of food, personal tastes, family views, disability or low levels of fitness, low self-esteem).

In depth

• If the underlying causes of overweight and obesity need to be assessed.
• If the person has complex disease states and/or needs that cannot be managed adequately in either primary or secondary care.
• If conventional treatment has failed in primary or secondary care.
• If specialist interventions (e.g. very-low-calorie diet for extended periods or surgery) may be needed.

In depth