Factors Impacting BMI

Although differences in the amount of body fat are the major reason that people of the same height may be a different weight, there are other contributors to a person's weight.

The BMI And Your Racial Characteristics

People of different races may have different body compositions, for example, they may have a lighter or heavier bone structure.

This means that for the same height and weight, people from two different races may be carrying different amounts of body fat, and therefore have different risks to their health.

The BMI and Asian people

To account for these differences, it is now recommended that:

• A BMI of 23 to 25.9 be considered indicative of overweight.
• A BMI of 26 to 29.9 be considered indicative of obesity class i.
• A BMI of 30 to 34.9¦ obesity class ii.
• A BMI of 35+ ¦¦obesity class iii.

In summary, an Asian person is generally considered overweight when their total weight is lower than an equivalently tall white European person.

The BMI and Polynesian people

It is now recommended that:

• A BMI of 26 to 31.9 is considered indicative of overweight.
• A BMI of 32 or above is considered indicative of obesity.

Generally, Polynesian people are considered overweight at a slightly higher weight than white Europeans.

Muscularity and level of fitness

Muscle tissue weighs more than the same volume of fat tissue.

This means that if you weighed yourself holding an icecream container full of muscle, the scales would read higher than if you weighed yourself holding an icecream container full of fat tissue. If you replaced most of your body fat with the same volume of muscle you would therefore weigh more, even though you would have much less fat and would generally be considered healthier.

People who build up a lot of muscle bulk can therefore be quite heavy, compared to other people of their height. The BMI number cannot detect that the weight is due mainly to extra muscle tissue, not fat. For this reason, the BMI is not as accurate in people who are well muscled.

Aging

As people age, muscle tissue is slowly broken down and replaced with fat. Such a person's weight on the scales may remain stable, but their proportion of body fat, and therefore the risks to their health are rising. Because the weight is not changing, the BMI will also remain stable. Therefore the BMI cannot pick up this type of increase in body fat.

Dieting

When people diet to lose weight a proportion of the weight lost is always muscle tissue, especially if the weight loss is rapid (The body breaks down whatever tissue is easiest to give it the energy it needs to function, and it can be easier for the body to break down muscle than fat, particularly if those muscles are not being used).

This is particularly so if the dieter is not involved in an exercise program to keep their muscles stimulated, and therefore, strong. In this case, weight, and therefore BMI would drop, but the proportion of body fat may not change much at all.

Also, when the weight is regained, it will almost all be regained as fat, rather than as muscle. This is why it is important that weight loss programs be accompanied by adequate activity/exercise.