5.4.1  Measurements of fat-mass (fatness)

As you read earlier Body Mass Index (BMI) is the weight of a person in kilograms divided by their height in metres squared. A non-pregnant adult is considered to have a normal BMI when it falls between 18.5 and 25 kg/m2. Table 5.2 shows you the different categories of nutritional status based on a person’s BMI.

Table 5.2  Cut-off values for BMI for assessing adult nutritional status.

BMI(Kg/m2) cut-offsNutritional status
more than 40.0Very obese
30.0-40.0Obese
25-29.9Overweight
18.5-24.9Normal
17-18.49Mild chronic energy deficiency
16-16.9Moderate chronic energy deficiency
less than 16.0Severe chronic energy deficiency

If an adult person has a BMI of less than 16 kg/m2 they will not be able to do much physical work because they will have very poor energy stores. In addition they will be at increased risk of infection due to impaired immunity.

Risk of mortality and morbidity is related to the nutritional status as assessed by the BMI. If people are too fat or too thin their health suffers. The risk of mortality and morbidity increases with a decrease in the BMI. Similarly, when the BMI increases to over 25 kg/m2, the risk of mortality and morbidity increases. The relationship between BMI and risk of morbidity and mortality is shown in Figure 5.6.

Graph showing relationship between BMI and morbidity and mortality
Figure 5.6  Relationship between BMI and morbidity and mortality.
  • What are the problem associated with having high (greater than 25kg/m2) or low (less than 18.5 kg/m2) BMI?

  • The risk of mortality and morbidity increases with a decrease in the body mass index. Similarly, when the body mass index increases over 25 kg/m2, the risk of mortality and morbidity as well as other diseases such as hypertension, diabetes mellitus and cancer also increases.

5.4  Anthropometric measurements used to assess body composition

5.4.2 Measuring fat-free mass (muscle mass)