Rationale and impact
These sections briefly explain why the committee made the 2022 and 2023 recommendations and how they might affect practice.
Based on their expertise, the committee agreed that a clear benefit of measuring the waist-to-height ratio is that people can easily do it themselves, interpret their results, and seek advice if they are at increased health risk.
Self-measurement may reduce the sense of discomfort or stigma some people may feel from a healthcare professional doing the waist circumference measurement. People can also use resources to help them measure their waist accurately, such as the NHS BMI healthy weight calculator, and videos by Diabetes UK and the British Heart Foundation.
When a person seeks advice because self-measurement indicates an increased health risk, they may need further assessment (such as for cardiometabolic risk factors) and their waist-to-height ratio may be measured again. The committee were aware that there may be situations when a professional taking a measurement may have a negative effect or be inappropriate because of the stigma attached to it. And some people may not want to be measured because of their religious and cultural beliefs. The committee agreed on the importance of being sensitive to people's needs and recognising when it is not appropriate to measure. The committee noted that sensitivity and stigma will be addressed in a forthcoming update of the guideline.
The committee looked at evidence from studies on the accuracy of different measures for predicting or identifying health conditions associated with overweight and obesity, including type 2 diabetes and cardiovascular disease. The quality of the evidence was mixed. Most studies included information on how accurate the measures were at predicting or diagnosing the health risks associated with overweight and obesity, in people of different ethnicities. Overall, the studies showed that body mass index (BMI), waist circumference, waist-to-hip ratio and waist-to-height ratio could all accurately predict or identify weight-related conditions. The committee noted that BMI is still a useful practical measure, particularly for defining overweight and obesity. But they emphasised that it needs to be interpreted with caution because it is not a direct measure of central adiposity. The committee highlighted that waist-to-height ratio offers a truer estimate of central adiposity by using waist circumference in the calculation. Based on evidence and their experience, they agreed that using waist-to-height ratio as well as BMI would help give a practical estimate of central adiposity in adults with a BMI under 35 kg/m2. This would in turn help professionals assess and predict health risks. But because people with a BMI over 35 kg/m2 are always likely to have a high waist-to-height ratio, the committee recognised that it may not be a useful addition for predicting health risks in this group.
BMI is the main measure for defining overweight and obesity, and the committee did not alter the BMI categories for the general population. But, based on their expertise, they agreed it was important to estimate central adiposity when assessing future health risks, including for people whose BMI is in the healthy weight category. The committee also highlighted the need for caution when interpreting BMI in adults with high muscle mass because it may be less accurate in this group.
Age-related changes in the body are not well captured by BMI. The committee agreed that BMI should therefore be interpreted with caution in people aged 65 and over because their functional capacity may be reduced due to conditions such as age-related spinal disorders or sarcopenia. They also recognised that slightly higher BMI in older people can have a protective effect (for example, reduced risk of all-cause mortality) because they are less likely to be experiencing undernutrition. So, it is important for professionals to evaluate the balance of these risks when interpreting BMI.
The committee also highlighted that people from Black, Asian and minority ethnic family backgrounds are prone to central adiposity and have an increased cardiometabolic health risk at lower BMI thresholds. For example, studies in people of South Asian and Chinese family backgrounds showed an increased risk at a BMI of 21 kg/m2 to 26 kg/m2, whereas people from white family backgrounds showed increased risks at 25 kg/m2 to 29 kg/m2.
There was also some evidence for using lower BMI thresholds for people from Middle Eastern (Arab and Iranian), Black African, Black Caribbean and other Asian (Japanese, Korean and Thai) family backgrounds. For these groups, studies identified an increase in risk at BMI values that ranged from 21 kg/m2 to 30 kg/m2, but most were below 25 kg/m2. The committee noted that these lower thresholds are in line with international guidance and are already used in practice to refer people from these family backgrounds to weight management services.
Although NICE found no evidence on the thresholds for obesity classes 2 and 3 in people of these family backgrounds, the committee consensus was that it is generally good practice to reduce the thresholds used for the general population by about 2.5 kg/m2. This would mean that the threshold for obesity class 2 would be lowered to roughly 32.5 kg/m2, and for class 3 to 37.5 kg/m2 in these populations. Public Health England guidance on adult weight management and the British Obesity and Metabolic Surgery Society guidance on accessing tier 4 services also endorsed reducing the thresholds.
In line with their recommendations for other populations, the committee used the terms overweight and obesity instead of risk levels to describe thresholds in people with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background. They agreed that in their experience there was more stigma attached to talking about risk than overweight or obesity. They noted that terms such as 'high risk' could result in anxiety and overinterpretation of risk more than terms such as 'living with obesity'.
The committee also discussed the accuracy of waist-to-height ratio boundary values in predicting and identifying health risks. The evidence showed that the cut-off from individual studies was generally around 0.5 for all ethnicities and sexes, which was in line with the wider evidence. They agreed that waist-to-height ratio could be used to define central adiposity in adults, and that a range of 0.5 to 0.59 corresponds to increased health risks. The committee noted that a waist-to-height ratio of 0.6 or more indicates a further increase in risk.
The committee agreed that a key benefit of using waist-to-height ratio is that the classification is the same for all ethnicities and sexes. It can also be useful in adults with high muscle mass, for whom BMI may be less accurate.
Although there was a large evidence base, the committee noted a lack of evidence on the accuracy of methods for predicting future risks for people of some ethnicities. Few studies were based in the UK, so the evidence might not reflect how accurate different measures might be when used in a UK context. Therefore, the committee highlighted the need for more research on measurements and boundary values for different ethnicities and made a recommendation for research on measurements for assessing health risks in adults.
The committee agreed that it is important for healthcare professionals to ask for permission before starting any discussions linked to overweight, obesity and central adiposity.
Based on their experience, the committee stressed the importance of sensitive and positive discussions because the stigma associated with obesity can affect people's mental and physical health. This can lead to further weight gain and make them less likely to engage with healthcare professionals. It is especially important to be sensitive when talking to people with conditions such as eating disorders (such as anorexia nervosa, bulimia and binge eating disorder), or disordered eating (such as restrictive dieting, compulsive eating or skipping meals).
The committee noted existing resources and advice that could help conduct sensitive, person-centred conversations. These include Health Education England's healthier weight competency framework, Obesity UK's language matters, and training courses by the Royal College of General Practitioners (RCGBP), World Obesity Federation and European Association for the Study of Obesity (EASO).
The committee did not make specific recommendations on sensitive language and measures to prevent stigma because a forthcoming update of this guideline will address these.
The committee noted it is important for adults to know the long-term health risks and conditions associated with overweight, obesity and central adiposity. These include type 2 diabetes, cardiovascular disease, hypertension, dyslipidaemia, certain cancers, and respiratory, musculoskeletal or other metabolic conditions (such as non-alcoholic fatty liver disease). Knowledge about these may encourage the person to stick to a weight loss strategy. Based on their understanding of practice, the committee stressed the importance of an all-round discussion of the person's individual needs and preferences to reach a shared decision about what level and types of intervention would suit them. This includes taking into account factors such as ethnicity, weight-related comorbidities, socioeconomic status, family medical history and special educational needs and disabilities (SEND). These discussions can also involve giving information about local weight management services and other support services.
Based on their expertise, the committee agreed people with weight-related comorbidities may benefit from a higher level of intervention. They also highlighted groups of people, such as those newly diagnosed with type 2 diabetes and those with BMI over 50, who would benefit more from immediate weight management interventions. Based on their expertise, the committee noted that these groups are often not offered appropriate interventions early enough.
The committee highlighted that encouraging self-measurement is in line with changes in practice over the past 2 years, particularly the increase in carrying out initial assessments by phone. It has already become standard practice to use self-reported measurements such as weight, blood pressure readings and blood sugar levels for conditions such as diabetes.
Using waist-to-height ratio as well as BMI would likely have minimal cost impact because tape measures are already routinely available in NHS settings for measuring waist circumference.
The committee noted that community pharmacies have been involved in taking measurements as well as it being done in general practice. Health Education England's healthier weight competency framework highlights that healthcare professionals involved in identification of overweight and obesity should be able to accurately measure and classify weight status. With the addition of waist-to-height ratio, it is important that training is available so that measurements can be conducted by trained personnel.
Currently, there are no established resources for calculating waist-to-height ratio, but resources such as the NHS BMI healthy weight calculator can be used to explain how to take waist measurements. Additional training programmes may need to be developed to help healthcare professionals understand central adiposity and conduct waist measurement in a sensitive manner and with care, especially in people with specific conditions such as eating disorders. This will lead to additional training costs. There may also be a cost increase associated with the extra staff time needed to teach people how to measure themselves and calculate waist-to-height ratio. But the committee agreed that these additional costs are unlikely to result in a significant resource impact and will be balanced out by the long-term health improvements such as decreased risk of developing diabetes or cardiovascular disease.
Using lower BMI thresholds in people from Black, Asian and minority ethnic family backgrounds will increase the number of people who are eligible for weight management services. However, this could reduce levels of overweight and obesity and thereby reduce the costs of treating obesity-related conditions for the NHS and wider system, such as social care systems.
There may be challenges in using BMI or waist-to-height ratio in people who have a physical disability, some physical conditions (such as scoliosis) or learning difficulties because people may be unable to get on scales independently or be lifted safely. In such circumstances, reasonable adjustments would be needed for adults, for example using seated or hoist scales, or scales that can be used for wheelchairs (including moulded wheelchairs). Measurements may also need to be modified, for example using sitting height or demi-span (the distance between the mid-point of the sternal notch and the finger roots with the arms outstretched laterally) instead of overall height, meaning specialist assessment may be needed. It may also be challenging to take measurements in people who are housebound because it may not be possible to access equipment such as specialist scales during home visits.
The committee were aware of the need to update advice on sensitivity when taking measurements, remaining mindful and sensitive to children and young people's needs (including cultural and religious beliefs) as well as the needs of their parents and carers, and recognising when it is not appropriate to measure. They did not make any recommendations because this section will be reviewed as part of a forthcoming update of the guideline.
The committee looked at evidence on the accuracy of different measures for predicting or identifying health conditions associated with overweight and obesity, including type 2 diabetes and cardiovascular disease. The quality of the evidence was mixed. Some studies included information on how accurate measures were at predicting or diagnosing the health risks associated with overweight and obesity in children and young people of different ethnicities.
Overall, the committee agreed that the studies showed that BMI, waist circumference and waist-to-height ratio could all be used to accurately predict or identify weight-related conditions when they were adjusted for age and sex. The same was true of waist-to-height ratio when it was not adjusted for age and sex. They discussed that BMI z-score adjusted for sex and age tended to be the most accurate measure for identifying different health conditions, but waist-to-height ratio was often equally accurate and, in some studies, more accurate. (BMI z-score is also known as BMI standard deviations [SDs], which indicate how many units a child's BMI is above or below the average BMI value for their age group and sex.)
Based on the evidence and their clinical expertise, the committee agreed that BMI is a useful practical measure for estimating and defining overweight and obesity. However, they noted that BMI should not be interpreted in the same way for children and young people as for adults. Healthcare professionals should use charts that are specific to children and young people and adjusted for age and sex. The committee also noted that waist-to-height ratio is a truer estimate of central adiposity, which is related to health risks.
The committee agreed that special growth charts may be needed when assessing children and young people with cognitive and physical disabilities, including those with learning disabilities. They noted that growth charts for children and young people with Down's syndrome are available from the Centres for Disease Control and the Royal College of Paediatrics and Child Health.
The committee agreed that the evidence for using waist-to-height ratio as a practical estimate for central adiposity to assess and predict health risk in children and young people was not as good as the evidence for adults. They agreed that it could still be useful as an indication of future health risks. But they stated that more research was needed on the accuracy of different measures and made a recommendation for research on measurements for assessing health risks in children and young people.
The committee looked at evidence for different boundary values for BMI and BMI z-scores but these focused on identifying current health conditions rather than defining the degree of overweight and obesity. Based on their expertise, they provided clinical definitions of overweight and obesity using BMI centiles and BMI SDs. These values correspond with those in the Royal College of Paediatrics (RCPCH) and Child Health UK-World Health Organization (WHO) growth charts. The committee agreed that it was important to use clinical judgement when interpreting BMI below the 91st centile, especially because children and young people in the healthy weight category may still have central adiposity.
The committee also noted that there are resources that can help professionals understand how to measure, plot and assess BMI in children and young people. These include educational resources from the RCPCH and the National Child Measurement Programme Operational Guidance, which both give information on how the clinical definitions of BMI link to BMI centiles and SDs.
There was a lack of evidence identified on BMI boundary values for children and young people from different ethnicities. The committee agreed this was an important area for research to investigate whether there are variations in thresholds, as there are in adults, and made a recommendation for research on measurements for assessing health risks in children and young people. The committee noted that although they could not provide different thresholds for BMI, waist-to-height ratio could be used as an indicator of central adiposity regardless of ethnicity and sex.
Studies also suggested that the optimal waist-to-height ratio cut-offs for children and young people ranged from 0.42 to 0.57, with most studies averaging around 0.5. Based on the evidence and their clinical knowledge, the committee agreed the waist-to-height ratio boundary value of 0.5 should be the same for children and young people as for adults.
The committee agreed that it is important to ask for permission from children, young people, and their parents or carers (if appropriate) before starting any discussions linked to overweight, obesity or central adiposity. They agreed that professional judgement is needed to ensure discussions are age appropriate and decide whether the child or young person should be involved. They also noted that it was standard practice for healthcare professionals to use Gillick competency to determine the capacity of a child or young person under 16 to consent.
Based on their expertise, the committee stressed the importance of sensitive and positive discussions because the stigma associated with obesity can affect a child or young person's mental and physical health. It is especially important to be sensitive when talking to children and young people with conditions such as eating disorders (such as anorexia nervosa, bulimia and binge eating disorder), or disordered eating (such as restrictive dieting, compulsive eating or skipping meals).
The committee noted existing resources and advice that could help conduct conversations with children and young people in a sensitive and positive way. These include Health Education England's healthier weight competency framework, Public Health England's let's talk about weight (which highlights a focus on weight maintenance and growing into a healthier weight, rather than weight loss) and Obesity UK's language matters guide. There are also training courses by the Royal College of General Practitioners (RCGBP), World Obesity Federation and European Association for the Study of Obesity (EASO).
The committee did not make specific recommendations on sensitive language and measures to prevent stigma because a forthcoming update of this guideline will address these.
Based on their clinical expertise, the committee agreed that tailored interventions were useful for children who are living with overweight or obesity or have increased health risk based on waist-to-height ratio. They agreed that weight-related comorbidities, ethnicity, socioeconomic status, social complexity (for example, looked-after children and young people), family medical history, mental and emotional health and wellbeing, developmental age, and special educational needs and disabilities (SEND) need to be taken into account when tailoring interventions.
The committee were particularly aware that children and young people with weight-related comorbidities, such as type 2 diabetes, may benefit from a higher level of intervention regardless of their waist-to-height ratio. The committee stressed the importance of working with the child or young person, and their families and carers (if appropriate), to make an informed decision about the treatment or care option that is best for them. As highlighted in resources such as the step-by-step guide produced by Public Health England on conversations about weight, healthcare professionals can also give information about local weight management services and other support services during these discussions.
Waist-to-height ratio is not routinely measured in practice, so there may be additional costs for the extra staff time involved. But the cost impact should be small because waist measurements are already widely used in primary care, so it would not need much extra time to calculate the ratio.
The committee noted that health visitors and school nurses, as well as general practice, are involved in taking measurements. Health Education England's healthier weight competency framework does highlight that healthcare professionals involved in identification of overweight and obesity should be able to accurately measure and classify weight status in children and young people. With the addition of waist-to-height ratio, it is important that training is available so that measurements can be conducted by trained personnel.
There are no established resources for measuring waist-to-height ratio, but healthcare professionals can use the NHS BMI healthy weight calculator, and videos by organisations such as Diabetes UK and the British Heart Foundation. These are for adults but can also be useful for older children and young people, families and carers.
There are a few training programmes specifically for managing overweight and obesity in children and young people, such as the ones by the World Obesity Federation, European Childhood Obesity Group, the Department of Health and Social Care's obesity team and Health Education England. Some of these need to be updated to include measuring waist circumference and interpreting waist-to-height ratio, which might lead to additional training costs. Healthcare professionals may need extra time to teach older children and young people, and their families and carers, how to measure the waist accurately and calculate waist-to-height ratio. However, the committee agreed that additional costs of training and staff time are unlikely to result in a significant resource impact and are justified by the long-term health benefits associated with a reduction in obesity-related conditions.
There may be challenges in using BMI or waist-to-height ratio in children and young people with physical disabilities, some physical conditions (such as scoliosis) or learning difficulties. Reasonable adjustments would also be needed for children and young people using wheelchairs (including moulded wheelchairs) such as using seated or hoist scales, or scales that can be used for wheelchairs. And although there is published guidance on supporting people with learning disabilities in obesity and weight management, there are no validated proxy measurements for height in children and young people (for example, using their sitting height or demi-span to estimate their height). This makes taking measurements difficult in children and young people with physical disabilities or learning difficulties.
The committee discussed evidence on bariatric surgery for various subgroups of people with and without obesity-related comorbidities. They agreed that it improved several important outcomes (including weight loss, cardiovascular disease and mortality) for people with a BMI of 40 kg/m2 or more and for those with a BMI of 35 kg/m2 or more if they had obesity-related comorbidities. They also agreed that giving examples of common health conditions that could be improved by bariatric surgery would help practitioners decide whether referral was appropriate for those with a BMI below 40 kg/m2. This list was based on the evidence identified for this guideline and is therefore not exhaustive. They agreed that the economic evidence showed that bariatric surgery was cost effective in these groups.
Committee members highlighted that referral to a specialist weight management service for comprehensive assessment for surgery from a weight management multidisciplinary team was important to ensure that the risks associated with the surgery are identified and managed.
The committee discussed whether non-surgical measures should be tried, including interventions in specialist weight management services (referred to as tier 3 services in NICE's 2014 guidance) before assessing people for surgery. They agreed that making people try specific measures before referral for surgery would create an unjustified barrier to effective treatment, and the evidence did not support using surgery only as a last resort. They also noted that tier 3 services are not available in all parts of the country (in 2014 to 2015, only about 21% of the clinical commissioning groups in England included these services), and that information on them was limited. So restricting assessment for surgery to those who have already used a tier 3 service could exacerbate health inequalities.
No evidence was found on the effectiveness of bariatric surgery for weight loss in people who had been refused other treatment because of obesity, such as a kidney transplant, fertility treatment or joint replacement surgery. The committee could not identify a referral criterion for this population so they made a recommendation for research on bariatric surgery in people who are unable to receive treatment for other conditions.
Although no evidence was found on the effectiveness of bariatric surgery in different ethnicities, the committee agreed that, based on their experience, obesity-related comorbidities affected people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family backgrounds at lower BMI levels. Lowering the BMI thresholds for offering surgery to people in these groups could improve outcomes. The committee also agreed that reducing the BMI threshold by 2.5 kg/m2 was supported by evidence identified for the recommendations on identifying and assessing overweight, obesity and central adiposity. They noted that this would be in line with guidance developed by other organisations (for example, British Obesity and Metabolic Surgery Society guidance on accessing tier 4 services and joint guidance from the American Society for Metabolic and Bariatric Surgery and International Federation for the Surgery of Obesity of Metabolic Disorders). However, they also made a recommendation for research on bariatric surgery in people from minority ethnic family backgrounds to confirm the appropriate referral criteria.
Committee members highlighted that although bariatric surgery can be effective for weight loss and improve comorbidities, there are short- and long-term medical, nutritional (for example, deficiencies), surgical and psychological risks and complications that may be associated with the procedure. They noted that another major concern was the lack of service provision and variation in practice, including in the initial assessment before surgery.
Based on these risks and concerns, the committee agreed it was crucial to stress the importance of an initial comprehensive assessment by a multidisciplinary team to determine the level of risk before surgery. And that, to manage the variation in practice, it was important to give health and social care professionals and anyone being referred for assessment information about what to expect during this assessment and the level of support the person will need.
The committee agreed on the importance of comprehensive assessment, including assessing the person's fitness for anaesthesia and surgery, by a multidisciplinary team that has access to or includes people with specialist expertise. Although these specialist assessments were recommended in NICE's 2014 guideline, the committee agreed they were not yet universal practice, so it was useful to restate their importance.
The committee agreed that ideally the multidisciplinary team should have access to or include a physician, surgeon or bariatric surgeon, registered dietitian and specialist psychologist. But they acknowledged that because of variation in commissioning of services there may be differences in the structure of the multidisciplinary team and that this assessment for surgery might currently lie in tier 3 or tier 4 services. The committee also noted that various factors need to be taken into account when carrying out the assessment to ensure that the person's needs are met. For example, if the person has comorbidities, specialist input from other multidisciplinary teams already involved in their care may be needed, or input from a learning disability team or liaison nurse if they have learning disabilities or neurodevelopmental conditions. So they did not recommend specific membership of the team to account for flexibility for local arrangements and individual needs.
The committee agreed that assessing the person's previous weight management attempts and engagement with weight management interventions can help identify which interventions have been successful or unsuccessful in the past and aid discussions about future treatment decisions. This can also allow people to be assessed for surgery even if they have not been able to access appropriate weight management interventions because of a lack of local availability.
The committee noted the importance of taking into account other factors linked with health inequalities that may affect someone's response after surgery, for example, managing their weight after surgery.
Access to expertise in all these areas would allow the team to identify people for whom bariatric surgery is suitable, and identify any arrangements needed before surgery such as managing existing or new comorbidities, improving nutrition or providing psychological support.
Offering assessment for bariatric surgery to people even if they have not tried all non-surgical measures or have not already attended a tier 3 service for intensive weight management support will reduce variation in practice and increase uptake in previously overlooked groups. Considering assessment for bariatric surgery at lower BMI thresholds for people from some ethnicities will reduce inequalities in obesity-related outcomes and improve accessibility of treatment.
These are both likely to increase the number of referrals and surgeries carried out, and therefore increase costs. But basing the offer of surgery on comorbidities as well as BMI will help those who could benefit most, and the cost will be offset by the long-term reduction in obesity-related complications.