What is the difference between BMI and Body Fat Percentage?
To answer the question of the difference between BMI and body fat percentage we need to understand what each one measures and how the measurement is calculated.
Because excessive body fat predisposes an individual to a plethora of metabolic disorders, body fat percentage is a useful tool for gauging overall health. With this in mind it is important for any individual undertaking a health and wellness programme to track progress in a quantifiable way. This is where body fat measurement becomes vital.
The most commonly used method in the medical community is BMI however the fitness community tends to prefer the measurement of body fat percentage.
But what is BMI?
BMI is the abbreviation for Body Mass Index and is used to calculate the overall fat content of a person’s body. It is a mathematical calculation that divides weight in kilograms by height in meters. Essentially the person’s weight is being compared to their height then shown as a percentage.
BMI is a very simple calculation and doesn’t require any particularly specialized equipment, however it does not allow for differences in body type. As different body types have varying characteristics that will affect overall body weight this renders the result less accurate. For example, in the case of athletic individuals they will have a greater percentage of muscle in proportion to fat and therefore weigh more than non athletic people of the same height. BMI reading would put many athletes and fitness workers into the obese category.
As a rule of thumb it is generally considered that underweight in adults ranges from 18 – 24.9%, normal 25 – 29.9% and 30% of above is in the overweight to obese category.
Body Fat Percentage
Body fat is a necessary structural component of the body. It is a connective tissue and like all connective tissues it binds, supports and protects. For example almost 4% of the body’s weight is made up of the fat deposits surrounding the vital organs (in a healthy adult).
Body fat percentage simply means the amount of fat in a body in proportion to the amount of lean mass. Fat includes everything from the fat stores in the superficial layers of the body to the intramuscular fat and the tissue surrounding and protecting vital organs. Lean body mass is generally thought of as muscle but includes bones and other tissues that are not fat.
Calculating Body Fat Percentage
Equipment such as a hydrostatic tank or a skin fold calipers are needed to measure body fat accurately. Body type is considered in these cases but not height or weight.
Electronic methods such as hand-held devices and smart weight scales use bio impedance to measure body fat and also factor in height and weight however they are considered to be less accurate for athletes.
Calculating body fat percentage is still considered a little more complicated than BMI. Hydrostatic weighing, the cream of body fat measuring equipment, is both expensive and requires very specialized, bulky equipment. Skin fold calipers are less expensive and more portable but both require skilled individuals to do calculations. With the introduction of new technology body fat measurement is likely to be more commonly used by both the fitness and the medical professions.
The norms for body fat percentage vary for different categories of individual. See the table below.
|Athletic||6 – 13%||14 – 20%|
|Healthy/Active||14 – 17%||21 – 24%|
|Average||18 – 24%||25 – 31%|
Women over 32 percent and men over 25 percent are considered obese.
Too little body fat is as unhealthy as having too much and balance is needed. Levels and distribution of body fat will vary depending on gender and age. In females the majority of fat is stored around buttocks, thighs and abdomen where for males it is mostly around the waist.
Research has shown that women who have a waist size of more than 30 inches have a higher risk of diabetic problems and other heart ailments. Likewise, women who have a BMI of 25 or less, and who have less overall fat content, are less prone to diseases.
So BMI or Body Fat?
Body Mass Index (BMI) is measured by dividing the weight of the body by the height of the particular person but The BMI is limited in determining the general health of a person, whereas body fat plays an important role in determining possible health hazards.
A person’s BMI should be maintained at a certain level, but healthy level of body fat often depends on a person’s age and gender.
With the above points in mind it is clear that both have advantages and disadvantages. Lifestyle, accessability and general health will play a role in deciding which to use.