JJ Virgin4x NYTimes Best Selling Author, Certified Nutrition Specialist, Fitness Hall of Famer

How to Track Fat Loss and Muscle Gain | Bioimpedance, DEXA, and Waist-to-Hip Ratio Explained

28 Aug 2025 · 3 min

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In this instructional video, JJ Virgin explains practical methods for monitoring body composition changes during fat loss and muscle gain. She starts by describing how consumer bioimpedance scales work: a low‑level electrical wave travels through the body, and resistance (impedance) is higher in fat than in lean tissue. The scale estimates total body water, which correlates with skeletal muscle because muscle stores water and glycogen. Virgin warns that hydration and carbohydrate intake affect readings, so measurements must be taken under consistent conditions (same time of day, after bathroom, same hydration and carb status). She advises tracking the trend of total body water over a week rather than day‑to‑day fluctuations; an upward trend in water alongside weight loss indicates muscle preservation or growth while losing fat. The scale also provides an estimate of visceral adipose tissue, but the most accurate assessment comes from a DEXA scan, which visualizes fat and muscle distribution. For at‑home monitoring, she recommends a Bluetooth tape measure (e.g., Renpho) to record waist and hip circumferences weekly. Two key ratios are highlighted: waist‑to‑height (waist should be ≤ ½ of height) and waist‑to‑hip (≤ 0.8 for women, ≤ 1.0 for men). These simple measurements serve as proxies for visceral fat levels. Overall, the video offers a step‑by‑step framework combining technology (bioimpedance, DEXA) and low‑tech tools (tape measure) to reliably track body composition progress.

Chapters

now a bioimpedance scale. What it does is it sends a wave up your body and it checks the resistance to it. That resistance is fat. The more fat, the more resistance, the less fat, the less resistance. And what it's going to do is it's going to give you an estimate of something called your total body water. Now, the more muscle you have, the more total body water you have, because that's where we're going to take water and carbohydrates and store them as glycogen in our muscles. So Higher body water, higher skeletal muscle mass. And that is the equation that the, the machine will give you total body water and then make a guesstimate, right, of your skeletal muscle mass. So you may initially, let's say that you step on a scale after doing a very low-carb diet for a week, it might look like you lost muscle because you dehydrated yourself and you lost glycogen in your muscles. So you have to know what you're looking at. You want to keep your conditions the same when you're doing these things. The the same amount of hydration, the same amount of carbohydrates, weighing in at the same time each day, preferably in the morning. You wake up, you go to the bathroom, then you do this. And then what you're going to look at with this bioimpedance machine and the total body water is you're going to look at the trend over time. So you— it's going to bounce each day because again, it's based on hydration. And then what you'll do is you'll look at the end of the week and you'll look at the trend. And what you want to see is you want to see that your total body water is muscle went up and that your weight is going down. If that is happening, that shows that you're holding onto or building muscle while you're losing body fat. And the machine will also tell you, oh, you've lost some body fat. Now it will also give you your visceral adipose tissue, but it's also guessing this. The best way to really identify that is both with the DEXA body scan, where it really gives you a picture of where your fat is, right? And where your muscle is and how much muscle you have. And then what you can do at home is you can use a tape measure. And I like to use a Bluetooth tape measure. There's one called Renpho, R-E-N-P-H-O. We'll put the info in the show notes. And what's cool about this is that it is a Bluetooth feature. It reports to your phone and you can track your trends. All you need to do is once a week do a waist to hip ratio. So you can do a waist measurement, a hip measurement, and then you look at two things. What's my waist to height ratio? Because you want your waist to be half of the measurement of your height or less. So if you're 72 inches tall, that means you're 36 inches or less on your waist. And then a waist to hip. And as a woman, you want your waist to hip ratio to be 0.8 or less. And if, if it's a man, 1 or less. So that's the way you can really track that visceral adipose tissue at home is through a simple waist and hip measurement.