Adults who are overweight or obese

The body mass index (BMI) of an adult is used to assess if they are overweight or obese. The following table shows the cut-off points for a healthy weight or of being overweight or obese:

BMI classifications
Classification BMI (kg/m2)

Healthy weight

18.5 to 24.9


25 to 29.9

Obesity I

30 to 34.9

Obesity II

35 to 39.9

Obesity III

40 or more

BMI is a less accurate indicator of adiposity (whether someone is overweight or obese) 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. 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 (23 kg/m2 to indicate increased risk and 27.5 kg/m2 to indicate high risk) to trigger action to reduce the risk of conditions such as type 2 diabetes, has been recommended for black African, African–Caribbean and Asian (South Asian and Chinese) groups.

Alcohol consumption

One unit is 10 ml or 8 g of pure alcohol. This equals one 25 ml single measure of whisky (alcohol by volume [ABV] 40%) or one-third of a pint of beer (ABV 5%) or half a standard (175 ml) glass of wine (ABV 12%).

It is recommended, to keep their risk from alcohol low, that women and men should not regularly consume more than 14 units per week (UK Chief Medical Officers' guidelines on alcohol consumption). 'Regularly' means drinking this amount most weekdays of the month. For hazardous drinking (increasing risk drinking) and harmful drinking (high-risk drinking) definitions see the glossary in NICE's guideline on alcohol-use disorders: prevention.


BMI is commonly used to measure whether adults are a healthy weight, underweight, overweight or obese. It is defined as the weight in kilograms divided by the square of the height in metres (kg/m2).

Children who are overweight or obese

More than 1 classification system is used in the UK to define whether children are overweight or obese. The National Child Measurement Programme for primary care states that BMI should be plotted onto a gender-specific BMI chart for children (UK 1990 chart for children older than 4 years). Children over the 85th centile, and on or below the 95th centile, are categorised as overweight. Children over the 95th centile are classified as obese. Other surveys, such as the Health Survey for England also use this system. However, in clinical practice the 91st and 98th centiles may be used to define 'overweight' and 'obesity' respectively. Children on or above the 98th centile may also be described as very overweight. See Public Health England's 'A simple guide to classifying body mass index in children'.

Dietary habits

This includes the food and drink (including alcoholic drinks) consumed, energy and nutrient intake, portion size and the pattern and timing of eating.

Energy balance

Energy balance is when energy intake from all food and drink (measured as calories or kilojoules) matches energy used for all bodily functions and physical activity. If energy intake is higher than energy used, a person will gain weight. If energy intake is less than energy used, a person will lose weight.

Energy density

Total energy content (kJ) divided by total weight (grams). Energy density can be calculated for individual foods, drink or for dietary intake as a whole. Lower energy dense foods, drinks or meals provide fewer calories per gram than higher energy dense foods, drinks or meals. High energy dense foods tend to be higher in fat or sugar and include crisps, nuts, confectionery, biscuits, cakes, full fat cheese and meat products. Low energy dense foods tend to be higher in water and lower in fat or sugar and include fruit and vegetables, soups and stews.

Energy intake

Daily energy intake is the total amount of energy consumed from foods and drinks. Estimated average requirements (EAR) for energy per day are recommended by the Scientific Advisory Committee on Nutrition (2011) as 10.9 MJ per day (2605 kcals per day) for adult men and 8.7 MJ per day (2079 kcals per day) for adult women. Daily EAR for children varies by age and gender.

Free sugars

Free sugars are sugars (monosaccharides and disaccharides) added to foods by the manufacturer, cook or consumer, and sugars naturally present in honey, syrups, fruit juices and fruit concentrates. Free sugars do not include lactose when it is naturally present in milk and milk products.

Healthy weight

For adults, a healthy weight is a BMI between 18.5 kg/m2 to 24.9 kg/m2. A healthy weight for children is dependent on their age and height (see 'Children who are overweight or obese' above).

Lifestyle weight management

Lifestyle weight management programmes for people who are overweight or obese 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 people 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 part of a comprehensive approach to preventing and treating obesity.

Moderate-to-vigorous physical activity

The 2019 UK Chief Medical Officers' physical activity guidelines set out physical activity recommendations. The definition of moderate-to-vigorous physical activity is included in the glossary of the report (see the UK Chief Medical Officers' physical activity guidelines for more information).

Non-nutritive sweetener

Non-nutritive sweeteners give food and drinks a sweet taste but include no (or virtually no) energy and no other nutrients. Non‑nutritive sweeteners are sometimes called low calorie, artificial or non‑caloric sweeteners.

Physical activity

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

Weight maintenance

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

Weight trajectory

A weight trajectory refers to a general pattern of weight gain or weight loss over many years.


Definitions of wholegrains vary but include whole wheat, whole wheat flour, wheat flakes, bulgur wheat, whole and rolled oats, oatmeal, oat flakes, brown rice, whole rye and rye flour and whole barley.