DESCRIPTIONS:

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 in classifying overweight and obesity in adult populations and individuals. It is defined as the weight in kilograms divided by the square of the height in meters (kg/m2).

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 as a rough guide because it may not correspond to the same degree of fatness in different individuals.

The World Health Organization (WHO) defines "overweight" as a BMI equal to or more than 25, and "obesity" as a BMI equal to or more than 30. These cut-off points provide a benchmark for individual assessment, but there is evidence that risk of chronic disease in populations increases progressively from a BMI of 21.

The new WHO Child Growth Standards, launched in April 2006, include BMI charts for infants and young children up to age 5. However, measuring overweight and obesity in children aged 5 to 14 years is challenging because there is not a standard definition of childhood obesity applied worldwide. WHO is currently developing an international growth reference for school-age children and adolescents.

Facts about overweight and obesity

WHO's latest projections indicate that globally in 2005:

• approximately 1.6 billion adults (age 15+) were overweight;
• at least 400 million adults were obese.

WHO further projects that by 2015, approximately 2.3 billion adults will be overweight and more than 700 million will be obese.

At least 20 million children under the age of 5 years are overweight globally in 2005.

Once considered a problem only in high-income countries, overweight and obesity are now dramatically on the rise in low- and middle-income countries, particularly in urban settings.

What causes obesity and overweight?

The fundamental cause of obesity and overweight is an energy imbalance between calories consumed on one hand, and calories expended on the other hand. Global increases in overweight and obesity are attributable to a number of factors including:

• a global shift in diet towards increased intake of energy-dense foods that are high in fat and sugars but low in vitamins, minerals and other micronutrients; and
• a trend towards decreased physical activity due to the increasingly sedentary nature of many forms of work, changing modes of transportation, and increasing urbanization.

What are common health consequences of overweight and obesity?

Overweight and obesity lead to serious health consequences. Risk increases progressively as BMI increases. Raised body mass index is a major risk factor for chronic diseases such as:

• Cardiovascular disease (mainly heart disease and stroke) - already the world's number one cause of death, killing 17 million people each year.
• Diabetes - which has rapidly become a global epidemic. WHO projects that diabetes deaths will increase by more than 50% worldwide in the next 10 years.
• Musculoskeletal disorders - especially osteoarthritis.
• Some cancers (endometrial, breast, and colon).

Childhood obesity is associated with a higher chance of premature death and disability in adulthood.

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, at the same time they are experiencing a rapid upsurge in chronic 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 even within the same household.
• This double burden is caused by inadequate pre-natal, infant and young child nutrition followed by exposure to high-fat, energy-dense, micronutrient-poor foods and lack of physical activity.

Get more information directly from
the National Institute of Health website.