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).
In 2016, more than 1.9 billion adults aged 18 years and older were overweight. Of these over 650 million adults were obese.
In 2016, 39% of adults aged 18 years and over (39% of men and 40% of women) were overweight.
Overall, about 13% of the world’s adult population (11% of men and 15% of women) were obese in 2016.
The worldwide prevalence of obesity nearly tripled between 1975 and 2016.
In 2019, an estimated 38.2 million children under the age of 5 years 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 Africa, the number of overweight children under 5 has increased by nearly 24% percent since 2000. Almost half of the children under 5 who were overweight or obese in 2019 lived in Asia.
Over 340 million children and adolescents aged 5-19 were overweight or obese in 2016.
The prevalence of overweight and obesity among children and adolescents aged 5-19 has risen dramatically from just 4% in 1975 to just over 18% in 2016. The rise has occurred similarly among both boys and girls: in 2016 18% of girls and 19% of boys were overweight.
While just under 1% of children and adolescents aged 5-19 were obese in 1975, more 124 million children and adolescents (6% of girls and 8% of boys) were obese in 2016.
Overweight and obesity are linked to more deaths worldwide than underweight. Globally there are more people who are obese than underweight – this occurs in every region except parts of sub-Saharan Africa and Asia.
For adults, WHO defines overweight and obesity as follows:
overweight is a BMI greater than or equal to 25; and
obesity is a BMI greater than or equal to 30.
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.
For children, age needs to be considered when defining overweight and obesity.
Children under 5 years of age
For children under 5 years of age:
overweight is weight-for-height greater than 2 standard deviations above WHO Child Growth Standards median; and
obesity is weight-for-height greater than 3 standard deviations above the WHO Child Growth Standards median.
Children aged between 5–19 years
Overweight and obesity are defined as follows for children aged between 5–19 years:
overweight is BMI-for-age greater than 1 standard deviation above the WHO Growth Reference median; and
obesity is greater than 2 standard deviations above the WHO Growth Reference median.
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 (including endometrial, breast, ovarian, prostate, liver, gallbladder, kidney, and colon).
The risk for these noncommunicable diseases increases, with increases 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.