6 Glossary

Adults who are overweight or obese

Adults are assessed to see if they are overweight or obese using their body mass index (BMI). The following are the cut-off points for a healthy weight or being overweight or obese:

  • Healthy weight, BMI (kg/m2) 18.5–24.9

  • Overweight, BMI 25–29.9

  • Obesity I, BMI 30–34.9

  • Obesity II, BMI 35–39.9

  • Obesity III, BMI 40 or more.

BMI is a less accurate indicator of adiposity in adults who are highly muscular, so it should be interpreted with caution in this group.

Waist circumference can also be used to assess whether someone is at risk of health problems because they are overweight or obese (up to a BMI of 35, see recommendation in NICE's guideline on obesity prevention). For men, a waist circumference of less than 94 cm is low risk, 94–102 cm is high and more than 102 cm is very high risk. For women, a waist circumference of less than 80 cm is low risk, 80–88 cm is high and more than 88 cm is very high risk.

The use of lower BMI thresholds to trigger action to reduce the risk of conditions such as type 2 diabetes has been recommended for black African, African–Caribbean and Asian groups. The lower thresholds are 23 kg/m2 to indicate increased risk and 27.5 kg/m2 to indicate high risk. (See recommendations on BMI and waist circumference for Black, Asian and minority ethnic groups in NICE's guideline on obesity identification, assessment and management.)

Behaviour change techniques

A collection of techniques that aim to help people change their behaviour to improve their health. The techniques are based on an established theory or rationale (see NICE guidance on behaviour change).

Body mass index

Body mass index (BMI) is commonly used to measure whether or not adults are a healthy weight or underweight, overweight or obese. It is defined as weight in kilograms divided by the square of height in metres (kg/m2).

Complex needs

'Complex needs' refers to issues that affect a person's health and wellbeing. They might include:

  • a behavioural issue such as substance misuse

  • specific conditions such as those limiting mobility or learning, mental health conditions, substantive or life-threatening comorbidities or dietary needs

  • personal social circumstances, such as homelessness.

Dietary habits

This includes a range of factors including the food and drink (including alcoholic drinks) consumed, energy and nutrient intake, portion size and the pattern and timing of eating. Population advice on food and nutrition is available on the NHS Choices website.

Lifestyle weight management programmes

Lifestyle weight management programmes for overweight or obese adults are multi-component programmes that aim to reduce a person's energy intake and help them to be more physically active by changing their behaviour. They may include weight management programmes, courses or clubs that:

  • accept adults through self-referral or referral from a health or social care practitioner

  • are provided by the public, private or voluntary sector

  • are based in the community, workplaces, primary care or online.

Although local definitions vary, these are usually called tier 2 services and are just one part of a comprehensive approach to preventing and treating obesity.

Physical activity

The full range of human movement, from competitive sport and exercise to active hobbies, walking, cycling and the other physical activities involved in daily living.

Physical activity instructor

A qualified physical activity instructor meets the fitness industry's agreed qualification standards and undertakes continued professional development. Instructors working with people referred from a GP or another health professional should hold level 3 membership of the Register of Exercise Professionals (or equivalent).


Stigma in relation to someone's weight may take the form of bullying, teasing, harsh comments, discrimination or prejudice based on a person's body size.

Tiers of weight management services

Different tiers of weight management services cover different activities. Definitions vary locally but usually tier 1 covers universal services (such as health promotion or primary care); tier 2 covers lifestyle interventions; tier 3 covers specialist weight management services; and tier 4 covers bariatric surgery.

Weight loss

In this guideline, weight loss refers to the amount of weight lost through a lifestyle weight management programme.

Weight maintenance

The maintenance of a specific weight (whether or not weight has been lost).

Weight regain

In this guideline, weight regain means regaining some or all of the weight that was lost during a lifestyle weight management programme. The prevention of weight regain refers to keeping to a lower weight than the person would have been if they had not lost weight in the first place. This is also referred to as being on a lower weight trajectory.

Weight trajectory

A weight trajectory refers to a general pattern of weight gain or weight loss over many years. Many adults gradually put on weight as they get older. This gradual increase in weight will be lower for someone who has lost weight during a lifestyle weight management programme, if they have not regained any of that lost weight.

  • National Institute for Health and Care Excellence (NICE)