Global Health – What are overweight and obesity?

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

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 divided by his or her height; 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 World Health Organization’s (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

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
  • a decrease in physical activity 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, housing, agriculture, transport, urban planning, environment, food processing, distribution, marketing and education.