What is BMI? Is it even relevant anymore? How do I measure my body fat?

Weight is a very personal matter. Everybody has a unique relationship with their body weight. In a past blog post, I’ve recounted my own personal experience (FAT). This blog post is different. This is a technical post relating to the body mass index (BMI) and body composition. Read on to learn how a number on a scale can be misleading and what other methods exist to determine body-fat.

BODY MASS INDEX (BMI)

BMI is used to determine the weight status of an individual. Using this metric, an individual’s weight status could range from underweight to obese. This is the formula to determine your BMI:

weight (lb) / [height (in)]2 x 703.

Fortunately for non-math folks, the Center’s for Disease Control and Prevention (CDC) has a nifty calculator you can use to determine your BMI (click here to try it out).

Unfortunately, this metric is not without it’s problems. A muscular yet lean person can weigh more and be categorized by BMI as overweight or obese despite the fact that they have low adipose tissue. Also, all adults are lumped together to determine BMI and ignores the fact that in general, women have more body fat than men and older people have more body fat than younger people. Despite these discrepancies, the CDC currently states that “the correlation between BMI and body fatness is fairly strong.”

Okay, so BMI is still a metric that can be used to determine an individual’s weight status but what is a more accurate measurement?

BODY COMPOSITION

We all need fat. Fat is necessary for energy and organs to function properly. This is why our bodies store fat, in order to secure an energy source. In fact, fat is mostly stored in adipose tissue throughout our bodies. Having an excess amount of adipose tissue is when health problems begin. For example, “large amounts of visceral adipose tissue are related to increased cardiac risk, type 2 diabetes, liver disease, and cancer.” You’re smart, you knew this already but I think it’s important to remember that fat is both good for your body and potentially life threatening. This is all well and good but how do you measure body-fat? Keep reading!

MEASURING BODY COMPOSITION

BMI used a simple formula to determine the weight status of a person, measuring body composition, on the other hand, is much more involved. One study compared several methods to determine the most accurate tool or method to determine body composition. The tools or methods they compared were hydrostatic weighing (densiotometry), air displacement plethysmography (ADP), bioelectrical impedance analysis (BIA), dual-energy X-ray absorptiometry, CT scans, and MRI scans. The study concluded that MRI imaging was the most accurate. You can read about this study here. Clearly, these are advanced methods that common folk do not have access to. So what is a more accessible method?

SKINFOLD MEASUREMENT TECHNIQUE

The skinfold measurement technique is the most common method used by personal trainers. It requires the use of specialty calipers and pinching various parts of a client’s body to gather the skin. The area’s are different for men and women. The calipers are used to measure the skinfold thickness at the pinched area. There is a very specific procedure that should be followed when getting these measurements. The measurements are then put into an equation to get body-fat results. There are different equations that could be used but “of the many equations for estimating body composition, two developed by Jackson and Pollock (1985) have the smallest margin of error for the general population.” This method yields “fairly accurate results.”

CONCLUSION

The intention behind this post is to differentiate between BMI and body composition and to show you the different types of methods that exist to determine body-fat. BMI may not seem like the most accurate metric to determine weight status but it is easy, quick and most importantly, it is not invasive. No one’s personal space is being invaded. In terms of determining body composition, the skinfold caliper measurement method is the most practical and accessible. However, it could mean putting your hands on an individual who may be sensitive about their body which is why I am weary of this method.

As a personal trainer, I encourage my clients to focus more on how they’ve progressed over time. I beam with pride when a client has gotten stronger or has completed a physical feat they could not complete in the past. This is progress. A number on a scale does not accurately depict this remarkable progress. I use the BMI and bio-electrical impedance scale to measure body fat percentage upon request but overall I tell my clients that if you are getting stronger, feeling good, and your old clothes are fitting better, that is success. Be proud.

I’m curious - would you be comfortable with a personal trainer administering the skinfold measurement technique? Let me know in the comments!

(Image: I found the picture on a copyright free website and I think that statue is absolutely amazing, stunning, and beautiful!)