In 2012, the mean BMI of adults in England was approximately 27 kg/m2. Adults with a healthy weight (BMI 18.5 to 24.9 kg/m2) were in the minority (32% of men and 41% of women). Most people were either overweight (BMI 25 to 30) or obese (BMI over 30). (See the glossary for a more detailed definition of adults who are overweight or obese.) Around 28% of children aged 2 to 15 were classified as either overweight or obese (The Health and Social Care Information Centre's statistics on obesity, physical activity and diet: England 2014). (See the glossary for a more detailed definition of children who are overweight or obese.)

Mean BMI among adults has increased by about 1.3 kg/m2 since 1993 and the proportion of adults classified as a healthy weight has decreased by about 9 percentage points between 1993 and 2012. ('Statistics on obesity, physical activity and diet: England 2014').

Population studies suggest that people's average weight increases gradually through life, for example, 1 UK‑based cohort study found adults gained about 0.2 kg per year (Rate of weight gain predicts change in physical activity levels: a longitudinal analysis of the EPIC-Norfolk cohort, Golubic et al. 2013).

Although overweight and obesity are common among all social groups, the prevalence increases with social disadvantage (Fair society, healthy lives: a strategic review of health inequalities in England post-2010, The Marmot Review). For example, among children, data from the National Child Measurement Programme suggests that obesity prevalence of the most deprived 10% of children is approximately twice that of the least deprived 10% (Public Health England's figures on health inequalities). Obesity is also linked to ethnicity: it is most prevalent among black African women (38%) and least prevalent among Chinese and Bangladeshi men (6%) (The NHS Information Centre's health survey for England 2004: the health of minority ethnic groups – headline tables.) Children and adults with disabilities are more likely to be overweight or obese (Public Health England's reports on obesity and disability – children and young people and obesity and disability – adults).

Being overweight or obese increases the risk of chronic and severe medical conditions (Foresight's project report on tackling obesities: future choices). Life expectancy is reduced by an estimated average of 2 to 4 years for people with a BMI of 30 to 35 kg/m2, and 8 to 10 years for people with a BMI of 40 to 50 kg/m2 (Body-mass index and cause-specific mortality in 900,000 adults: collaborative analyses of 57 prospective studies, Prospective Studies Collaboration).

Black African, African–Caribbean and Asian (South Asian and Chinese) groups are at risk at a lower BMI than white Europeans. 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 have been recommended for these groups. See NICE's guideline on BMI: preventing ill health and premature death in black, Asian and other minority ethnic groups. Lower BMI thresholds are also used trigger action in people with comorbidities such as type 2 diabetes.

Around 85% of people with hypertension have a BMI above 25 kg/m2, and 90% of those with type 2 diabetes have a BMI above 23 kg/m2 ('Tackling obesities: future choices – project report'). People who are obese may also experience mental health problems, stigmatisation and discrimination because of their weight. The cost to society and the economy of people being overweight or obese was estimated at almost £16 billion in 2007 (more than 1% of gross domestic product). It could rise to just under £50 billion in 2050, if obesity rates continue to increase unchecked ('Tackling obesities: future choices – project report'). Concerns have been raised that the increasing costs of treating people who are overweight or obese are unsustainable for the NHS and more action should be taken to prevent obesity (NHS England's get serious about obesity or bankrupt the NHS).

The Department of Health's healthy lives: a call to action on obesity in England aimed to reduce 'the level of excess weight average across all adults by 2020'. It advocated a 'life course' approach (that is, an approach for different key stages of life). It also stressed the importance of striking a balance between treating people who are already obese, and sustained, local action to prevent people becoming overweight or obese in the first place. Public Health England has also identified preventing obesity as a key priority for action (see Public Health England's from evidence into action: opportunities to protect and improve the nation's health).

Since the publication of NICE's guideline on obesity prevention in 2006, NICE has published a range of guidelines that draw on these recommendations or provide more specific advice. However, NICE has not made any further recommendations on how people can maintain a healthy weight or prevent excess weight gain.

A review of NICE's 2006 guideline on obesity in 2011 noted that new evidence may be available on how children and adults can maintain a healthy weight or prevent excess weight gain.

In addition, NICE's guideline on obesity: working with local communities, raised issues about the way messages and advice about weight are communicated, particularly the tone and language used.