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Background papers: Lifestyle and wider determinants :: Healthy weight [Update in progress] :: Obesity :: Summary

Overweight and obesity are terms used to describe increasing degrees of excess body fat. The prevention and treatment of overweight and obesity is a central public health policy goal. Excess weight is a significant risk factor for a number of diseases including type II diabetes, cancer and heart disease. Overweight and obesity can also affect mental health and self-esteem.

Excess weight is caused by an energy imbalance between 'energy in' (food consumption) and energy expenditure (energy used by the body during activity and metabolism).[1] If there is greater energy intake than is required, the excess energy will become excess fat. However, the underlying causes of this energy imbalance, which result in weight gain, are complex. Behavioural, psychological, social, cultural and environmental factors are thought to determine the increasing prevalence of obesity seen throughout the world.

Obesity in adults is measured and classified using the Body Mass Index (BMI) according to table 1.

  Body Mass Index
Underweight < 18.5
Healthy weight 18.5 – 24.9
Overweight 25.0 – 29.9
Obesity I 30.0 – 34.9
Obesity II 35.0 – 39.9
Obesity III < 40.0
Table 1: Classifying overweight and obesity using BMI (kg/m2)

The BMI classifications may be less accurate in highly muscular people. For some ethnicities, risk factors for obesity may occur at a lower BMI. The Scottish guidance [2] recommends that until specific cut-offs are validated, South Asian, Chinese and Japanese individuals may be considered overweight at BMI >23 kg/m2 and obese at BMI >27.5 kg/m2. Waist measurements are also used to assess the risk from overweight and obesity. Tables 2 and 3 detail the risks associated with an increased weight measurement.

  Low High Very high
Male <94 94–102 >102
Female <80 80–88 >88
Table 2: Waist circumference classifications
  Low High Very high
Overweight No increased risk Increased risk High risk
Obesity I Increased risk High risk Very high risk
Table 3: Waist circumference and risk associated with overweight and obesity

The relative health risks of health problems associated with obesity are shown in table 4.

Greatly increased risk
(Relative risk much
greater than 3)
Moderately increased risk
(Relative risk 2-3)
Slightly increased risk
(Relative risk 1-2)
Type II diabetes Coronary heart disease Cancer
Insulin resistance Hypertension Polycystic overy syndrome
Gallbladder disease Stroke Impaired fertility
Dyslipidaemia Osteoarthritis Low back pain
Breathlessness Hyperuricaemia Anaesthetic risk
Sleep apnoea Psychological factors
Table 4: Relative risks of health problems associated with obesity (Relative risk — risk measured against that of non-obese person of same age and sex)[1]

Childhood obesity, physical activity, diet and nutrition and breastfeeding (see pregnancy and maternities) are considered elsewhere.

Key issues and gaps

• Prevalence of obesity in Medway is estimated to be higher than the England average
• Prevalence of adult obesity (and therefore costs to the NHS and social care) are projected to rise without significant intervention.
• Obesity in adults is strongly correlated to obesity in children.
• Due to the high prevalence of overweight and obesity whole population approaches are required.
• National data shows that deprivation and low income is particularly related to higher prevalence of obesity
• National data and research suggests that groups at greatest health risk due to obesity are: pregnant women, women from African-Caribbean and Pakistani communities and people with physical and learning disability.


[1]   Swanton DK. Healthy Weight, Healthy Lives: A toolkit for developing local strategies 2008; National Heart Forum. .
[2]   Scottish Intercollegiate Guidelines Network. Management of Obesity, A national clinical guideline 2010; Scottish Intercollegiate Guidelines Network. .