Body fat, muscle, visceral fat and BMR: what each number means
A body composition scale reports a dozen numbers. Here is what each one means, how it is estimated, and how to use them without getting lost in daily ups and downs.
Short answer. Body fat is the share of your weight that is fat; muscle, water, protein and bone make up the rest. A scale estimates each from electrical resistance, and day-to-day changes are mostly water. Read the weekly trend of two or three numbers together rather than any single reading.
Body fat percentage
The share of your total weight that is fat. Some fat is essential: it protects organs and stores energy. Healthy ranges depend on age and sex, so ask your doctor or a dietitian what suits you. For tracking, the direction over several weeks matters more than any one reading.
Skeletal muscle and muscle mass
Skeletal muscle is the muscle you move on purpose: arms, legs, back, trunk. Keeping it while losing weight is a common goal, because muscle supports strength, movement and metabolism. A scale estimates muscle from how well your body conducts current.
Body water
Water makes up well over half of body weight. It moves up and down with food, drink, salt, exercise, heat and hormones, and these shifts are the main reason one day's reading can differ from the next. Body water is also why scales ask you to weigh in under similar conditions.
Visceral fat
Fat stored around the organs in your abdomen. Scales report a rating, not a measurement. A rating that is trending down is a good sign, but it is an estimate: treat it as a prompt to look at your habits, not a diagnosis.
Protein and bone mass
Protein is a portion of lean mass and bone mass an estimate of the mineral in your skeleton. Both are modelled rather than measured directly. They change slowly, so look at them over months.
BMR: basal metabolic rate
The energy your body uses at rest in a day. Scales estimate it with equations that use your age, sex, height, weight and, where possible, lean mass. It is a starting point for calorie targets, not an exact figure.
BMI and the body score
BMI is weight divided by height squared. It cannot tell fat from muscle, so two people with the same BMI can have very different bodies. A "body score" is a brand-specific summary and cannot be compared between brands.
Segment readings: arms, legs and trunk
Scales with hand grips and foot plates can report fat and muscle for each arm, each leg and the trunk. Compare left with right, and each part with what is typical for your height and sex. The Everhale app shows this as a body map, with fat as yellow tissue and muscle in red.
How to use the numbers
- Weigh in under the same conditions. The same time each morning, after the toilet, before food or drink.
- Look at the weekly average. Daily readings bounce around with water.
- Watch two or three numbers together. Weight down, body fat down and muscle steady or up is a good sign, even when weight alone barely moves.
- Change one habit at a time. Protein at each meal, a daily walk and two or three strength sessions a week are common starting points.
- Review after four to eight weeks. That is long enough for real change to show.
Common questions
Why does my body fat change from day to day?
Mostly water. Food, drink, salt, exercise and heat move body water, and the scale reads that as a change in fat or muscle. Use the weekly trend.
What is a good visceral fat rating?
Lower is generally better, but the scale of the rating and the cut-offs differ between brands. Treat it as a trend and ask your doctor about your own risk.
Is BMI useful?
As a quick population measure, yes. For one person it cannot separate fat from muscle, so body composition adds the information BMI misses.
Sources
Keep reading
- How to choose a body composition scale in NZ
- 8-electrode vs 4-electrode body fat scales
- How accurate are body fat scales vs DEXA?
- Are body composition scales safe? Pacemakers and pregnancy
Everhale is a wellness product, not a medical device. This guide is general information, not medical advice. Talk to your doctor or a dietitian about your own health.