Breaking it Down: Scale Weight vs. BMI vs. Body Fat Percentage

So many people live and die by their scale. They wake up, jump on the thing and the number that pops up predisposes them to a good day or a bad day. Let’s be honest – when that number is higher than we expect, all kinds of negative thoughts and feelings run through our heads. The purpose of this post is to get you thinking about what numbers you should actually be paying close attention to if your goal is to be healthy and fit. I’m purposely not going to include any graphs or charts for your reference. You can google those all day long. Just open your mind, take in the facts, and get real about what is truly important when tying your mood to a metric.

Body Weight
Weight, as we all know, is a measurement of an objects mass. A persons body weight includes all things contained within the walls of the skin- muscle, bones, organs, fat, water, etc., etc. It is very common for weight to fluctuate by several pounds from one day to the next, or even within the same day as your body’s various processes take place – digestion, exercise, recovery… It is important to remember that scale weight does not indicate how fit a person is. Consider that a female olympic volleyball player can weigh in between 160 and 180 and be far more fit than their sedentary counterpart who weighs less.

Body Mass Index (BMI)
Belgian polymath Adolphe Quetelet devised what we now know as the BMI equation in 1832 as a way to define the “normal man.”  He never intended for the equation (weight equals height squared) to be used to determine body fat — his project was intended to describe the standard proportions of the human build. In the 1970’s, over a century later, BMI started to be used by epidemiologists in studies of population health, but was quickly adopted by doctors who wanted a quick and easy classification for their patients. By 1985, the National Institutes of Health began using BMI to define whether someone was underweight, lean, average, overweight or obese. While I certainly don’t advocate dismissing your doctors directions as they may relate to your BMI, I don’t believe that BMI is an accurate indicator as to whether someone is healthy or not. I will use myself as an example. I currently weigh 135lbs and have a body fat percentage just under 20%. According to the BMI chart, I could lose another 18 pounds and still be considered lean, NOT underweight. I can honestly say that if that happened, I would look absolutely skeletal and put my health at risk. BMI is one number to consider as part of your total health picture, but it is by no means the end-all be-all.

Body Fat Percentage
Body fat percentage is a much more accurate and reliable metric by which to measure your health because it takes into consideration many more factors than just weight and height. Your overall body composition determines the percentage, so the calculation includes height, weight, gender, age, fat, muscle and skeletal tissue. I use a Bioelectrical Impedance Analysis (BIA) to determine the body fat percentage of my clients. The general principle behind BIA: two conductors are attached to a person’s body and a small electric current is sent through the body. The resistance between the conductors will provide a measure of body fat, since the resistance to electricity varies between adipose, muscular and skeletal tissue. Fat-free mass (muscle) is a good conductor as it contains a large amount of water (approximately 73%) and electrolytes, while fat is anhydrous and a poor conductor of electric current.

Body measurements
In addition to weight and body fat percentage, I also rely on body measurements to determine clients’ progress. A lot of people incorrectly state that a pound of muscle ways more than a pound of fat. The truth is a pound equals a pound. But a pound of muscle takes up far less space on the body than a pound of fat, so as a persons body fat percentage decreases, we should also be seeing decreases in inches across the body.

So what’s the best methodology for determining progress, fitness, and general health? Here’s my professional recommendation:
1) Weigh yourself once a week in the morning, preferably before eating and after a bowel movement.
2) If you work with a trainer, have your Body Fat Percentage calculated every 4-6 weeks.
3) Record your measurements every 4-6 weeks. This includes around the forearm, bicep, chest, natural waist, abdomen and hips. If you are spot training, you may also want measurements of the triceps, shoulders, or neck.