Why body mass index is wrong

A recent BBC News Health article raises the question, ‘Can we trust BMI to measure obesity?’ BMI stands for Body Mass Index. It uses height and weight to work out if a person is a healthy weight. It has been in use for over 100 years. But it has come into criticism of late. This follows revelations by UCLA psychologists that found 54 million Americans being labelled as ‘unhealthy’ after BMI, when in fact they were not.

Can BMI be trusted?

One study that sheds doubt on body mass index as a measurement of health or obesity, is the UCLA College study. Their findings include:

  • More than 30% of those with BMIs in the “normal” range are actually unhealthy based on their other health data.
  • More than 2 million people considered “very obese” because of a BMI of 35 or higher, are actually healthy.

What BMI is obese?

Other findings that reveal BMI to be inaccurate and misleading is that anyone with a BMI of 30 or more is obese. And being obese significantly increases the risk of diseases, such as diabetes, and premature death.

Yet there are studies demonstrating that some individuals who are obese have a lower cardiovascular risk and an improved metabolic profile. In addition, studies demonstrate there to be a subset of people with a ‘normal’ body mass index who are
metabolically unhealthy and have increased mortality risk.

Why BMI is flawed

In 2013, Nick Trefethen of Oxford University’s Mathematical Institute pointed out that BMI leads to confusion and misinformation. In fact, he says that it exaggerates thinness in short people and fatness in tall people.

“Because of that height2 term, the BMI divides the weight by too large a number for short people and too small a number for tall people. So short people are misled into thinking they are thinner than they are, and tall people are misled into thinking they are fatter than they are.”

The BBC News Health article also mentions bodybuilders and rugby players for example, who carry a lot of muscle. And because muscle is denser than fat, their BMI would class them as obese. Yet they have very little fat and will be very healthy.

Are body mass index and body fat the same?

BMI is a calculation of weight in kilo’s divided by height in metres squared. It doesn’t differentiate between fat and muscle mass. It also doesn’t measure how the fat is distributed throughout the body. And that matters. And this is another reason why BMI has come into question in recent years.

Research shows that people who carry a lot of fat around their waist are at a high risk of health problems. This is because the fat is stored around key organs in their abdomen. In fact, researchers for one study suggest that waist size is linked to risk of Type 2 Diabetes, regardless of BMI. So it seems that waist size might be a better monitor of health and obesity than BMI.

What body composition test is most accurate?

A more accurate measurement of health is body composition measurement. The reason being, body composition measurement can monitor changes in fat, lean mass and fluid. Consequently, it provides a better understanding of what’s happening inside the body.

Bodystat is an inexpensive, quick and non-invasive way of carrying out body composition measurement. It uses BIA (bio-electrical impedance) to accurately measure the amount of fat, lean muscle and water in the body.  It does this by using electrodes. These use a small, safe current, to measure raw data at any segment of the body. And by using different frequencies, the current penetrates different tissues. As a result, algorithms are able to calculate how much of that tissue is present in the body (from analysing the impedance to the flow of current at that frequency).

This video from Bodystat clearly explains how bioelectrical impedance works, and how it measures body fat, lean and water inside the body.

For accurately measuring statistics for body fat, lean muscle mass and hydration in the gym, the pocket-sized Bodystat 1500 Touchscreen is the latest model, based on the most popular device. However, the best choice for dieticians and nutritionists is the Bodystat 1500MDD. This is more advanced than the 1500, with added functions such as cellular health and nutritional status monitoring, as well as, overall fitness and health.

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