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Obesity and overweight

Fact sheet N°311
Reviewed May 2014


Key facts

  • Worldwide obesity has nearly doubled since 1980.
  • In 2008, more than 1.4 billion adults, 20 and older, were overweight. Of these over 200 million men and nearly 300 million women were obese.
  • 35% of adults aged 20 and over were overweight in 2008, and 11% were obese.
  • 65% of the world's population live in countries where overweight and obesity kills more people than underweight.
  • More than 40 million children under the age of 5 were overweight or obese in 2012.
  • Obesity is preventable.

What are overweight and obesity?

Overweight and obesity are defined as abnormal or excessive fat accumulation that may impair health.

Body mass index (BMI) is a simple index of weight-for-height that is commonly used to classify overweight and obesity in adults. It is defined as a person's weight in kilograms divided by the square of his height in meters (kg/m2).

The WHO definition is:

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

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.

Facts about overweight and obesity

Overweight and obesity are leading risks for global deaths. Around 3.4 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 2012, more than 40 million children under the age of 5 were overweight or obese. 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. In developing countries with emerging economies (classified by the World Bank as lower- and middle-income countries) the prevalence of childhood overweight and obesity in preschool children is in excess of 30%. 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).

What causes obesity and overweight?

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.

What are common health consequences of overweight and obesity?

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 2012;
  • diabetes;
  • musculoskeletal disorders (especially osteoarthritis - a highly disabling degenerative disease of the joints);
  • some cancers (endometrial, breast, and colon).

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.

Facing a double burden of disease

Many low- and middle-income countries are now facing a "double burden" of disease.

  • While they continue to deal with the problems of infectious disease and under-nutrition, they are experiencing a rapid upsurge in noncommunicable disease risk factors such as obesity and overweight, particularly in urban settings.
  • It is not uncommon to find under-nutrition and obesity existing side-by-side within the same country, the same community and the same household.

Children in low- and middle-income countries are more vulnerable to inadequate pre-natal, infant and young child nutrition At the same time, they are exposed to high-fat, high-sugar, high-salt, energy-dense, micronutrient-poor foods, which tend to be lower in cost but also lower in nutrient quality. These dietary patterns in conjunction with lower levels of physical activity, result in sharp increases in childhood obesity while undernutrition issues remain unsolved.

How can overweight and obesity be reduced?

Overweight and obesity, as well as their related noncommunicable diseases, are largely preventable. Supportive environments and communities are fundamental in shaping people’s choices, making the healthier choice of foods and regular physical activity the easiest choice (accessible, available and affordable), and therefore preventing obesity.

At the individual level, people can:

  • limit energy intake from total fats and sugars;
  • increase consumption of fruit and vegetables, as well as legumes, whole grains and nuts;
  • engage in regular physical activity (60 minutes a day for children and 150 minutes per week for adults).

Individual responsibility can only have its full effect where people have access to a healthy lifestyle. Therefore, at the societal level it is important to:

  • support individuals in following the recommendations above, through sustained political commitment and the collaboration of many public and private stakeholders;
  • make regular physical activity and healthier dietary choices available, affordable and easily accessible to all - especially the poorest individuals.

The food industry can play a significant role in promoting healthy diets by:

  • reducing the fat, sugar and salt content of processed foods;
  • ensuring that healthy and nutritious choices are available and affordable to all consumers;
  • practicing responsible marketing especially those aimed at children and teenagers;
  • ensuring the availability of healthy food choices and supporting regular physical activity practice in the workplace.

WHO response

Adopted by the World Health Assembly in 2004, the WHO Global Strategy on Diet, Physical Activity and Health describes the actions needed to support healthy diets and regular physical activity. The Strategy calls upon all stakeholders to take action at global, regional and local levels to improve diets and physical activity patterns at the population level.

The Political Declaration of the High Level Meeting of the United Nations General Assembly on the Prevention and Control of Noncommunicable Diseases of September 2011, recognizes the critical importance of reducing the level of exposure of individuals and populations to unhealthy diet and physical inactivity. The political declaration commits to advance the implementation of the WHO Global Strategy on Diet, Physical Activity and Health, including, where appropriate, through the introduction of policies and actions aimed at promoting healthy diets and increasing physical activity in the entire population.

WHO has developed the "Global Action Plan for the prevention and control of noncommunicable diseases 2013-2020" which aims to achieve the commitments of the UN Political Declaration on NCDs which was endorsed by Heads of State and Government in September 2011. This action plan aims to build on the WHO Framework Convention on Tobacco Control and the WHO Global Strategy on Diet, Physical Activity and Health. The action plan will contribute to progress on 9 global NCD targets to be attained in 2025, including a 25% relative reduction in premature mortality from NCDs by 2025 and a halting of the global obesity rates to those of 2010.

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