Obesity simply means an accumulation of body fat. In the medical world, it is determined by using the body mass index (BMI), which measures weight in relation to your height. To calculate your BMI, go to our Body mass index calculator.

Obesity is classified in three ways:

  • obese Class I (mild) - 20% to 40% overweight
  • obese Class II (moderate) - 41% to 100% overweight
  • obese Class III (severe) - more than 100% overweight (only occurs in 0.5% of obese people)

Causes of obesity in adulthood

Obesity in the United States is on the rise. In the last decade, the number of obese Americans has increased by 33%. Overall, 31% of men and 35% of women are obese.

  • Genetics: Research suggests that on average, genetics influence about 33% of body weight, however it may be more or less in a particular person.
  • Socioeconomics: Social status plays a big part in weight, especially among women. In the United States, obesity is twice as common among women in lower socioeconomic groups that in higher ones. Why this occurs is not fully understood, however, women in higher socioeconomic groups tend to have more time and resources for dieting and exercise.
  • Psychological: Two abnormal eating patterns, binge eating and night eating, may be triggered by stress, emotional upset, and a negative body image. Binge eating is similar to bulimia except that the binges are not followed by self-induced vomiting - meaning more calories are consumed.
  • Developmental: An increase in the size and/or number of fat cells adds to the amount of fat stored in the body. Obese people, particularly those who have been obese since childhood, may have five times more fat cells that people with normal weight.
  • Physical activity: A sedentary lifestyle is likely one of the main reasons for the increase in obesity - especially among people in affluent societies.
  • Brain damage: Damage to the brain, particularly the hypothalamus, accounts for a small percentage of obesity.
  • Drugs: A number of commonly used drugs cause weight gain including corticosteroids such as prednisones and antidepressants, as well as other drugs used to treat psychiatric disorders.
Written and reviewed by the MediResource Clinical Team