A body composition report breaks your weight into its component parts: fat, muscle, bone, and water. Instead of a single number on a scale, you get a detailed picture of what your body is actually made of. Most reports share a common set of metrics, but the terminology can be confusing if no one walks you through it. Here’s how to read each section and understand what the numbers mean for your health.
Body Weight Breakdown
The first section of most reports splits your total weight into two or three major categories. The simplest division is fat mass versus fat-free mass (also called lean body mass). Fat mass is all the stored fat in your body. Fat-free mass is everything else: muscle, organs, bone, and water. Some reports further separate bone mineral content from the lean tissue, giving you three compartments instead of two.
The key thing to understand is that lean body mass is not the same as muscle mass. Lean body mass includes your organs, blood, skin, and the water inside your body. Skeletal muscle mass, which many reports list separately, is the muscle tissue attached to your skeleton that you can actually train and grow. When you’re tracking progress from exercise, skeletal muscle mass is the number to watch. A gain in lean body mass could reflect water retention just as easily as muscle growth, so the more specific metric tells a clearer story.
Body Fat Percentage
Body fat percentage (often labeled PBF) tells you what fraction of your total weight is fat. This is generally more useful than fat mass in pounds or kilograms, because it accounts for your overall size. Two people can carry the same amount of fat but have very different body fat percentages if one has significantly more muscle.
Healthy ranges vary by age and sex. According to the World Health Organization, men ages 40 to 59 should aim for roughly 11% to 21% body fat, with the range shifting to 13% to 24% for men ages 60 to 79. Women naturally carry more essential fat and have correspondingly higher healthy ranges at every age. If your report shows a bar graph, you’ll typically see your result plotted against “under,” “normal,” and “over” zones calibrated for your demographic. A number in the normal zone doesn’t guarantee metabolic health on its own, but it’s a solid starting reference point.
Visceral Fat Level
Many analyzers, particularly Tanita devices, assign a visceral fat level (VFL) on a numbered scale. Visceral fat is the fat packed around your abdominal organs, and it behaves differently from the fat under your skin. It’s more metabolically active and more strongly linked to cardiovascular and metabolic disease risk.
On the Tanita scale, a rating between 1 and 12 indicates a healthy level of visceral fat. A rating of 13 or above signals excess. Some older guides describe a 1 to 20 scale, but the actual output can range higher. Regardless of the upper limit, the threshold that matters is 12 versus 13. If your number is creeping into the teens, that’s a signal to focus on reducing abdominal fat through sustained aerobic activity and dietary changes, even if your overall body fat percentage looks acceptable.
Where Your Fat Sits: Android vs. Gynoid
DEXA scans and some advanced analyzers report an android-to-gynoid fat ratio. “Android” fat is concentrated around the midsection (the classic apple shape), while “gynoid” fat sits around the hips and thighs (pear shape). The ratio compares these two deposits.
This ratio is one of the strongest predictors of metabolic risk on your entire report. Research in the Journal of Obesity found that the android-to-gynoid ratio explained nearly 46% of the variation in insulin resistance and was also closely tied to harmful cholesterol levels. That held true even in people whose overall weight was normal. A lower ratio (meaning relatively more fat in the hips than the belly) is generally favorable. If your ratio is climbing over time, it suggests fat is redistributing toward your midsection, which warrants attention even if your total fat mass hasn’t changed much.
Segmental Lean Analysis
This section divides your body into five segments: right arm, left arm, trunk, right leg, and left leg. For each segment, you’ll see how much lean mass (primarily muscle) is present. Most reports display two comparisons: one against the ideal value for someone your height, and one against your current body weight.
The practical use is spotting imbalances. If your right arm shows significantly more lean mass than your left, that asymmetry could indicate a training imbalance or a compensation pattern worth addressing. For the trunk, a low lean mass reading relative to the limbs might suggest weak core musculature. When comparing to the “ideal” bar, a reading at or above 100% means that segment is adequately developed. Below 100% means there’s room for improvement. Over time, these segment-by-segment numbers are useful for tracking whether a targeted exercise program is actually working where you want it to.
Body Water and the ECW Ratio
Your report may list total body water (TBW), intracellular water (ICW), and extracellular water (ECW). About two-thirds of your body water normally sits inside your cells, with the remaining third outside them in blood, lymph, and the spaces between tissues.
The number to pay attention to is the ECW/TBW ratio. In a healthy, well-hydrated person, roughly 33% of total body water is extracellular. When the ratio climbs meaningfully above that baseline (reports often flag values above 0.380 to 0.390), it can indicate fluid retention, inflammation, or edema. Higher ratios have been linked to poorer nutritional status and increased inflammation, since inflammatory processes make blood vessels more permeable, allowing fluid to leak into surrounding tissues. If your ECW ratio is elevated, it doesn’t necessarily mean something is wrong, but it’s worth discussing with a healthcare provider, especially if you notice swelling or have a chronic condition.
Phase Angle
Phase angle is a lesser-known metric that appears on some bioelectrical impedance reports. It reflects the integrity of your cell membranes, essentially how well your cells hold their structure and retain water where it belongs. Think of it as a measure of cellular quality rather than quantity.
A higher phase angle generally indicates healthier, more intact cells. It tends to decrease with aging and is correlated with nutritional status, disease severity, muscle strength, aerobic capacity, and even fall risk in older adults. People who exercise regularly, whether through resistance training or aerobic activity, consistently show higher phase angle values than sedentary individuals. There’s no single universal “good” number because it varies by age, sex, and body composition, but tracking your phase angle over time gives you a window into whether your overall cellular health is improving or declining.
Basal Metabolic Rate
Most reports include a basal metabolic rate (BMR) estimate, expressed in calories per day. This is the energy your body burns just to stay alive: keeping your heart beating, lungs breathing, and organs functioning while you do absolutely nothing. BMR typically accounts for 60% to 70% of your total daily energy expenditure.
The BMR on your report is more personalized than a standard online calculator because it’s derived from your actual lean mass and fat mass rather than just your height and weight. More muscle tissue means a higher BMR. To estimate how many calories you actually need in a day, you’d multiply your BMR by an activity factor (commonly 1.2 for sedentary, up to 1.9 for very active individuals). Your BMR alone is not your daily calorie target. It’s the floor, the minimum your body needs before any movement or digestion is factored in.
Getting Accurate Results
Body composition analysis, especially through bioelectrical impedance (the technology in most gym and clinic analyzers), is sensitive to your hydration and activity levels. The electrical current these devices send through your body travels through water, so anything that shifts your fluid balance will shift your results.
For the most reliable readings, keep conditions consistent each time you test. Research published in the International Journal of Sport Nutrition and Exercise Metabolism found that standardizing food, fluid intake, and physical activity for the 24 hours before testing significantly improved measurement precision. In practical terms: test at the same time of day, avoid heavy exercise that morning, eat and drink normally (but consistently), and skip alcohol the night before. Avoid testing right after a sauna, a large meal, or an intense workout. The goal isn’t one perfect scan. It’s a series of scans taken under similar conditions so that changes over time reflect real changes in your body, not just how much water you drank that day.
Most experts recommend retesting every 4 to 8 weeks rather than weekly. Body composition shifts slowly, and testing too frequently amplifies the noise from day-to-day fluid fluctuations, making it harder to see the signal of actual progress.