When you exercise, you expect your body composition to change, right? Ideally, you want to trim the fat and boost muscle. By doing this you lower your body fat percentage. That’s important since fat is metabolically inactive tissue and it releases inflammatory chemicals called cytokines. Plus, muscle tissue is more metabolically active. That’s important since having more of it relative to fat improves insulin sensitivity and metabolic health. You’re trying to idealize your body fat percentage not just to fit into a smaller pair of jeans you but to lower your health risks as well. That’s the power of exercise!
A chart can tell you whether you’re outside the ideal body fat range for your health, but, first, you have to know what your body fat percentage actually is. What’s the best way to measure your body fat percentage and to follow it to see if you’re making progress? Let’s look at a few of the ways that work and some that don’t work as well.
The Bathroom Scale
The bathroom scale – almost everyone has one and it’s the worst way to monitor your body fat percentage as it tells you very little. What you discover from the bathroom scale is whether your total body weight is going up or down. As you know, weight is made up of more than body fat. It corresponds to the weight of the muscle you have on your frame, the fluids in your body, body fat, and the weight of your organs. When it increases, it could be because you ate a meal high in salt last night and are retaining water. It could also be because you’re constipated and haven’t had a bowel movement, or because you’ve gained body fat. The scale doesn’t differentiate. You can have a normal body weight and still be “skinny fat” because your body fat percentage relative to muscle is too high. Don’t place too much value on the number you see on the bathroom scale.
BMI is another flawed measure. Like body weight, it says nothing about your body composition. What’s your body mass index? To calculate your BMI, divide your body weight in kilograms by your height in meters squared. The result is your BMI. It’s easier to use a BMI calculator online to get this value rather than doing the calculation. As you can see, BMI is determined by your total body weight relative to your height. The weight you carry could be mostly muscle or mostly fat and the formula doesn’t distinguish. In fact, based on BMI calculations, a ripped athlete could be classified as overweight because their muscular body weighs more. Like, the bathroom scale, BMI is lacking. Although the healthcare community still uses this measure, it’s a flawed model and completely useless for tracking body composition.
How about using a pair of calipers? Skinfold measurements are an inexpensive and relatively accurate way to determine body fat percentage. You can buy a caliper inexpensively and use it to measure skinfold thickness at various points on your body. Instructions for how to do this are online. Once you have the measurements, you average the values and use a formula to estimate your body fat percentage. It takes practice to get the measurements right as you need to grab the right amount of skin between the calipers. Studies show that the error rate for measuring absolute body fat percentage is as high as 5%. However, you can use skinfold measurements to monitor for changes in skinfold thickness. If the numbers rise, you know you’re gaining body fat.
Body Fat Scales
It sounds simple enough – step on a body fat scale and let it tell you your body fat percentage. Body fat uses bioelectrical impedance analysis to measure percentage of body fat. Muscle conducts electricity better than fat due to its higher water content and you can measure this using a body fat scale. However, studies show these scales aren’t particularly accurate and the results can be skewed by factors like hydration, when your last meal was, and when you last exercised.
Where a body fat scale can be useful is for monitoring for changes in body fat composition, but even for this to be accurate, you need to weight under standardized conditions. The best time is as soon as you wake up (for consistency). Even then, the results can be skewed by hydration status or salt intake.
More Advanced Ways
The gold standard for measuring body fat percentage is called a DEXA scan. This procedure, offered by health care centers, uses x-ray beams to measure body fat percentage. Despite being the so-called gold standard, research shows the results can vary by up to 10 percentage points due to factors such as the machine, state of health, and hydration status. So, it’s not extremely accurate, exposes you to radiation, and can be expensive.
Another more advanced way is the Bod Pod. Some health club and fitness centers offer this testing. To measure your body fat percentage, you sit in a sealed chamber while technicians measure how much air your body displaces. Unfortunately, this test isn’t particularly accurate either and the results can be off by 6 percentage points based on factors like moisture levels, clothing, and body temperature.
Finally, there’s hydrostatic weighing. This method compares your weight on land to your body weight when you’re completely submerged in water. By knowing the density of water, technicians can estimate your body composition. Unlike, the Bod Pod, hydrostatic weighing is accurate. However, you have to go to a site that offers it and it takes a little time. In general, the cost is not prohibitive. You can usually get this test done for under $100.00.
The Bottom Line
As you can see, not even the “gold standard,” DEXA is 100% accurate for measuring body composition. Don’t get too hung up on your body fat percentage. The important thing is to monitor changes over time and you can use inexpensive calipers to do that. Doing the technique properly is vital for accuracy, so make sure you read up and know how to take the measurements properly.
Muscle for Life. “How to Accurately Measure Your Body Fat Percentage”
Med Sci Sports Exerc. 2004 Jun;36(6):1070-7.