Obesity and Body mass index

August 9, 2021

Obesity implies the excess storage of body fats. The degree of obesity is assessed by comparison with the ideal weight for height, the Body Mass Index (BMI). BMI is calculated by using a simple formula:

Where kg is a person’s weight in kilograms and m2 is their height in meters squared. A BMI of 25.0 or more is overweight, while the healthy range is 18.5 to 24.9. Body fats can also be assessed by measuring skinfold thickness over the middle of the triceps muscle; the normal value for a man is 20 mm and 30 mm in a woman.

For Bedridden patients or people who can not stand, height can be estimated by measuring their Femoral length, knee height, arms span, half- span, or ulnar length (forearm), and then the height is calculated with the standard equations.

For adults 18-65 years men or women BMI is interpreted using the following standard weight status categories:

BMI (kg/m2) Weight Category
Below 18.5Underweight
18.5 – 24.9Normal or Healthy
25.0 – 29.9Overweight
30.0 and aboveObese
30.0 – 34.9Class I Obesity
35.0 – 39.9Class II Obesity
Greater or Equal to 40.0Class III Obesity

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BMI in children and teens (2-20) is interpreted in relation to other children of the same age and sex of a referring population as children are growing. Correlation between the BMI and body fat is fairly strong but even if two people have the same BMI, their level of body fat may differ. BMI is a useful way of identifying over-nutrition or under-nutrition but cannot discriminate between lean body or muscle mass and fat mass. A relatively high BMI can be due to high body fat or high lean body mass. A trained healthcare provider should perform appropriate health assessments to evaluate an individual’s health status and risks.

  • Women tend to have more body fat than men.
  • Blacks have less body fat than Whites, and Asians have more body fat than Whites.
  • Older people on average, tend to have more body fat than younger adults.
  • Athletes have less body fat than non-athletes.

Causes of obesity

Most patients suffer from simple Obesity. In certain conditions obesity is an associated feature; even in these situations, intake of calories must exceed expenditures. Hormonal imbalance is often incriminated in women e.g. in postmenopausal women or when taking contraceptive pills, but most weight gain in such cases is due to water retention.

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People get obese when they eat more calories than they burn through activity.

Conditions in which obesity is an associated feature

  • Genetics syndrome associated with hypogonadism e.g. Prader Willi Syndrome, Laurence-Moon-Biedl Syndrome
  • Hypothyroidism
  • Cushing’s Syndrome
  • Stein-Leventhal Syndrome
  • Drug-induced e.g. corticosteroids
  • Hypothalamic damage e.g. due to trauma, tumor.

Health Consequences of Obesity

Obese people are at increased risk for many diseases and health conditions, including the following: 

  • Hypertension, increase cholesterol leading to ischemic heart disease and strokes.
  • Type-2 Diabetes
  • Fatty liver and gallstones.
  • Osteoarthritis
  • Sleeping and breathing problems.
  • Chronic inflammation and increased oxidative stress.
  • Some cancers associated with overweight and obesity, (endometrial, breast, colon, kidney, gallbladder, and liver)
  • Psychological effects, anxiety, and depression.
  • Back strain
  • Hernias
  • Varicose veins
  • Reproductive disorders in men and women.

Morbidity and Mortality

There is an increase in mortality in obese patients, mainly from diabetes, coronary heart disease, and, cerebrovascular disease. The greater the obesity, the higher the morbidity and mortality. Weight reduction reduces this mortality and therefore should be strongly encouraged.


Treatment includes lifestyle modification such as diet, physical activity and behavior, and medicines or bariatric (weight loss) surgery for certain patients.

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