Not a day goes by that I don’t encounter someone who says they want to lose weight. Whether it be a client at the gym, a personal friend or family member, or the person I overhear talking in the grocery checkout line. There is always someone out there who wants to “lose weight”. However, what they usually mean is “lose fat”.

There are two commonly used measurements to indicate how “fat” or “lean” a person is: body fat percentage and body mass index (BMI). Which one is more accurate? Which one should you believe? Let’s sort out the differences and see.

What is BMI?

Body Mass Index is a measurement which assigns a numerical rating to your health based upon your weight and height. BMI is a tool used by many researchers and physicians to estimate a healthy body weight for you based upon your height. It is also used as an indicator of your health status and increased risk for certain diseases, such as type 2 diabetes, heart disease, and some forms of cancer. As your BMI increases, your risk of disease is also believed to increase.

What is Body Fat Percentage?

Body fat percentage is simply the percentage of your body weight that is composed of fat. If you weigh 175 pounds, and you are measured at 25% body fat, 44 pounds of your overall weight is fat composition. Your remaining 131 pounds is composed of lean mass (bones, muscle, organ tissue, blood, etc.).

How does BMI compare with Body Fat Percentage?

BMI may be an indicator of the connection between your weight and disease risks. However, it does not distinguish fat from muscle. BMI may give a rough estimate of body fatness – but there are individuals (i.e. muscle dense athletes) who appear overweight by the BMI standards who are not over fat. For instance, consider Joe who is 5’11”, weighs 182 pounds, has rugged muscle definition, strength trains and performs cardiovascular exercise regularly and carries little to no visible fat around his chest and belly. By the BMI chart below, Joe is overweight and at higher risk for disease. Now, compare him with Charlie. He is also 5’11” and 182 pounds, yet his midsection is soft and jelly-like, and he neglects to take part in a regular exercise regimen. According to the BMI chart, Joe and Charlie share the same BMI of 25.5. Hence, they are both considered to be overweight and at heightened risk for disease. Logic indicates that this just doesn’t add up.

From: http://www.consumer.gov/weightloss/bmi.htm

A body fat analysis would give a much clearer picture of their body compositions by deciphering what percentage of Joe’s and Charlie’s bodies are fat and what percentage is lean mass.

Keep in mind, a certain amount of body fat is necessary for your body to function properly. It’s needed to control body temperature, insulate and protect your organs, as well as provide energy storage for your body when needed.

The table below explains what constitutes a “healthy” body fat percentage:

How is body fat percentage tested?

There are a myriad of techniques used to estimate body fat percentage: DXA-scan (x-ray technology), skin fold test, bio-electrical impedance analysis, BOD POD air displacement theory, hydrostatic water tank testing. Each test form works differently and may net a slightly different result. If you choose to track the progression of your body fat percentage, what remains most important is that you use results from the same testing technique each time, so you are comparing “apples to apples”.

What’s the Verdict?

I am not discounting BMI as a useful tool when determining the status of someone’s health. However, when determining if someone is a healthy weight, I recommend the body fat percentage method because it is more individualized. It truly considers the composition of an individual’s body, not just where he or she falls on a height-weight chart. Tracking your body fat percentage can also help you determine if your weight loss goals are realistic.  If you get your body fat percentage to a healthy level, you WILL be much healthier and reduce your likelihood of disease.

Other References: www.webmd.com/diet/features/body-fat-measurement