Different weight classes are defined based on a person's body mass index (BMI) as follows:

  • healthy weight: 18.5 kg/m2 to 24.9 kg/m2

  • overweight: 25 kg/m2 to 29.9 kg/m2

  • obesity I: 30 kg/m2 to 34.9 kg/m2

  • obesity II: 35 kg/m2 to 39.9 kg/m2

  • obesity III: 40 kg/m2 or more.

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.

Overweight and obesity is a global problem. The World Health Organization predicts that by 2015 approximately 2.3 billion adults worldwide will be overweight, and more than 700 million will be obese. (World Health Organization obesity and overweight: fact sheet 311).

Obesity is directly linked to a number of different illnesses including type 2 diabetes, fatty liver disease, hypertension, gallstones and gastro-oesophageal reflux disease (see NICE's guidelines on gallstones and gastro-oesophageal reflux disease), as well as psychological and psychiatric morbidities. In 2011/12 there were 11,740 inpatient admissions to hospitals in England with a primary diagnosis of obesity: 3 times as many as in 2006/07 (Health and Social Care Information Centre's statistics on obesity, physical activity and diet – England, 2013). There were 3 times as many women admitted as men.

In the UK obesity rates nearly doubled between 1993 and 2011, from 13% to 24% in men and from 16% to 26% in women. In 2011, about 3 in 10 children aged 2 to 15 years were overweight or obese.

Ethnic differences exist in the prevalence of obesity and the related risk of ill health. For example, compared with the general population, the prevalence of obesity is lower in men of Bangladeshi and Chinese family origin, whereas it is higher for women of African, Caribbean and Pakistani family origin.

The cost of being overweight and obese to society and the economy was estimated to be almost £16 billion in 2007 (over 1% of gross domestic product). The cost could increase to just under £50 billion in 2050 if obesity rates continue to rise, according to the Department of Health's obesity projections. A simulated model reported in the Lancet predicted that there would be 11 million more obese adults in the UK by 2030, with combined medical costs for treatment of associated diseases estimated to increase by up to £2 billion per year (Wang et al. Health and economic burden of the projected obesity trends in the USA and the UK).

NICE's previous guideline on obesity (NICE guideline CG43) made recommendations for providing care on preventing and managing overweight and obesity. The guideline aimed to ensure that obesity became a priority at both strategic and delivery levels. In 2013, however, the Royal College of Physicians' action on obesity: comprehensive care for all identified that care provision remained varied around the UK and that the models used to manage weight differed. It also reported that access to surgery for obesity in some areas of the UK did not reflect the recommendations in NICE's obesity guideline.

The evidence base for very-low-calorie diets has expanded since the publication of NICE's obesity guideline in 2006, and their use has increased. However, these interventions are not clearly defined, and there are concerns about safety, adherence and the sustainability of weight loss.

NHS England and Public Health England's joined up clinical pathways for obesity working group report was published in March 2014. Comments from national and local stakeholder organisations were invited, mainly concerning implementation at a local level and implications for delivery.

Obesity surgery (also known as bariatric surgery) includes gastric banding, gastric bypass, sleeve gastrectomy and duodenal switch. It is usually undertaken laparoscopically. NICE guideline CG43 recommended that surgery should be an option in certain circumstances. In 'Bariatric surgery for obesity' the former National Obesity Observatory reported a rise in bariatric surgery from around 470 in 2003/04 to over 6,500 in 2009/10. The First Annual Report (March 2010) of the National Bariatric Surgery Register reported that more than 7,000 of these operations were carried out between April 2008 and March 2010.

The National Confidential Enquiry into Patient Outcome and Death review of the care of people who underwent bariatric surgery identified in 2012 that there should be a greater emphasis on support and follow up for people having bariatric surgery. The report also noted that clear postoperative dietary advice should be provided to people because of the potential for significant metabolic change (such as vitamin B12 and iron deficiency) after surgery.

It has been suggested that resolution of type 2 diabetes may be an additional outcome of surgical treatment of morbid obesity. It is estimated that about 60% of patients with type 2 diabetes achieve remission after Roux‑en‑Y gastric bypass surgery. It has also been suggested that diabetes-related morbidity and mortality is significantly lower after bariatric surgery and that the improvement in diabetes control is long-lasting (Keidar, Bariatric surgery for type 2 diabetes reversal: the risks).

NICE's guideline on obesity was reviewed in 2011, leading to this update. This guideline addresses 3 main areas: follow‑up care packages after bariatric surgery; the role of bariatric surgery in the management of recent-onset type 2 diabetes; and very-low-calorie diets including their effectiveness, and safety and effective management strategies for maintaining weight loss after such diets.

Safeguarding children

Remember that child maltreatment:

  • is common

  • can present anywhere, such as emergency departments and primary care or on home visits.

Be aware of or suspect abuse as a contributory factor to or cause of obesity in children. Abuse may also coexist with obesity. See NICE's guideline on child maltreatment for clinical features that may be associated with maltreatment.

This section has been agreed with the Royal College of Paediatrics and Child Health.

  • National Institute for Health and Care Excellence (NICE)