Overweight and obesity:

• are defined as abnormal or excessive fat accumulation that may impair health;
• have important consequences for morbidity, disability and quality of life;
• entail higher risk of developing type 2 diabetes, cardiovascular diseases, several common forms of cancer, osteoarthritis and other health problems; and
• are serious public health challenges in the WHO European Region.

Overweight and obesity are often measured using the BMI (Body Mass Index) scale. BMI:

• is a simple index commonly used to classify overweight and obesity in schoolchildren and adults;
• is calculated as a person’s weight (in kg) divided by his or her height (in m2); and
• does not distinguish weight associated with muscle from weight associated with fat and therefore provides only a crude measure of fatness.

BMI provides the most useful population-level measure of overweight and obesity as it is the same for both sexes and for all ages of adults. However, it should be considered a rough guide because it may not correspond to the same degree of fatness in different individuals.

The WHO definitions of overweight and obesity are:

• a BMI greater than or equal to 25 is overweight
  a BMI greater than or equal to 30 is obesity

Overweight and obesity are the fifth leading risk for global deaths. At least 2.8 million adults die each year as a result of being overweight or obese. In addition, 44% of the diabetes burden, 23% of the ischaemic heart disease burden and between 7% and 41% of certain cancer burdens are attributable to overweight and obesity.

Some WHO global estimates from 2008 follow.

• More than 1.4 billion adults, 20 and older, were overweight.
  Of these overweight adults, over 200 million men and nearly 300 million women were obese.
  Overall, more than 10% of the world’s adult population was obese.

In 2011, more than 40 million children under the age of five were overweight. Once considered a high-income country problem, overweight and obesity are now on the rise in low- and middle-income countries, particularly in urban settings. More than 30 million overweight children are living in developing countries and 10 million in developed countries.

Overweight and obesity are linked to more deaths worldwide than underweight. For example, 65% of the world’s population live in countries where overweight and obesity kill more people than underweight (this includes all high-income and most middle-income countries).

The fundamental cause of obesity and overweight is an energy imbalance between calories consumed and calories expended. Globally, there has been:

• an increased intake of energy-dense foods that are high in fat; and
• an increase in physical inactivity due to the increasingly sedentary nature of many forms of work, changing modes of transportation, and increasing urbanization.

Changes in dietary and physical activity patterns are often the result of environmental and societal changes associated with development and lack of supportive policies in sectors such as health, agriculture, transport, urban planning, environment, food processing, distribution, marketing and education.

Raised BMI is a major risk factor for noncommunicable diseases such as:

• cardiovascular diseases (mainly heart disease and stroke), which were the leading cause of death in 2008;
• diabetes;
• musculoskeletal disorders (especially osteoarthritis – a highly disabling degenerative disease of the joints);

The risk for these noncommunicable diseases increases, with the increase in BMI.

Childhood obesity is associated with a higher chance of obesity, premature death and disability in adulthood. But in addition to increased future risks, obese children experience breathing difficulties, increased risk of fractures, hypertension, early markers of cardiovascular disease, insulin resistance and psychological effects.