Body fat percentage and body composition: what the scales don't show
You've been walking more, lifting a bit, eating a little better, and the scales haven't moved. Or they've gone up. It's easy to decide that nothing is working.
Australians search for "body fat percentage" around 9,900 times a month, and "body composition" another 1,600 times, so it's clearly on a lot of minds. This piece explains what body composition means, why one number on the scales can only tell you so much, and a way of looking at your own trend that's kinder and more useful than chasing a target.
What body composition means
Your weight is one number: everything you are, all at once. Body composition breaks that number into parts. In everyday terms, the parts that come up most are:
- Body fat: the share of your weight that's fat. It's often shown as a percentage.
- Lean mass: the rest of you that isn't fat, including muscle.
- Body water: the water your body holds, which shifts with what you drink, eat and do through the day.
Two people can weigh exactly the same and have very different body composition. And the same person can stay the same weight for months while their body changes underneath, for example by building some muscle while losing a little fat.
Why the scales and BMI only tell part of the story
Body mass index (BMI) is a number worked out from your weight and height. It's quick and useful as a rough guide, and your GP may use it. But healthdirect, the Australian Government's free health information service, is clear about its limits: BMI can't tell how much of your weight is muscle and how much is fat. It notes that BMI is less accurate for some groups, including some high-performance athletes, weightlifters and pregnant women, and that its usefulness can depend on your body shape, age and sex.
healthdirect also explains that waist circumference can be used as a guide to fat around the middle, which is part of the picture too. That's a conversation for your GP, who can put any measurement in context for you.
The bathroom scales have the same blind spot as BMI. If you've started strength training, a number that stays put may simply mean your body is changing in ways the scales can't see.
Is there a "healthy" body fat percentage?
The honest answer is that there isn't one number that suits everyone. Body fat differs between people for many reasons, including age, sex, genetics and how active you are. Different ways of measuring it can also give different results, so a figure from one method won't always match another.
That's why a chart of "ideal" body fat percentages is best taken as background rather than a goal. If you'd like to know what's right for you, your GP is the best person to ask. What you can see for yourself is which way your own numbers are moving over weeks and months.
Why your own trend matters more than one reading
Body composition estimates move around from day to day. Body water in particular shifts with how much you've had to drink, a big meal, a hard training session or a hot day. One reading tells you very little on its own.
The useful part is the direction over time. Is your lean mass holding steady while you change your routine? Is body fat drifting one way over a couple of months, or just moving up and down around the same middle? Comparing you with you is far more helpful than comparing yourself with a chart or a friend.
That's the idea behind Personal Baseline Intelligence, which asks two plain questions: is this normal for you, and which way is it moving? As you wear the Thrive Band, Thrive learns your everyday patterns and builds a personal baseline. It starts as Emerging while Thrive is still getting to know you, and becomes Established once enough consistent information has been collected. Our piece on Personal Baseline Intelligence after 50 explains more.
How Thrive shows your body composition
The Thrive Band uses bioimpedance (Bio-Z) sensing to estimate body fat, lean mass and body water from your wrist. It sends a tiny signal through the body, so there's no separate scale to buy, find or remember to step on. Body composition isn't something the Band updates in the background. When you want a reading, you take one using the electrode on the Band, and your result shows up in the Thrive app, alongside your training, sleep, activity and what you eat.
A few things make it easier to live with:
- No screen on your wrist. The Band has no display, so there's no number looking back at you during the day. Your data waits in the Thrive app on your phone until you choose to look.
- Ask Thrive. You can ask about your own patterns in everyday language, such as "How has my lean mass changed since I started training twice a week?" or "What else was going on the month my body fat went up?", and get a plain-English answer back.
- The correlations engine. Over time, Thrive can show which habits tend to go with the changes you see, such as more regular strength sessions, more sleep or more consistent meals.
- One place for the whole routine. Thrive tracks your walks, runs and rides with GPS in the app, alongside your activity, workouts, plans, training programmes and nutrition logging, so your body composition isn't sitting on its own.
Like any estimate from a wrist band, body composition makes most sense as a trend over weeks, rather than a verdict on a single morning. You can see more on our features page.
Muscle, strength and everyday movement
If you're building a routine, body composition gives you more to go on than weight alone. The Australian Government's physical activity guidelines for adults recommend muscle-strengthening activities on two or more days a week, alongside 30 minutes or more of moderate to vigorous activity on most days. The recommendations for adults 65 and over include muscle strengthening on two or more days a week too, with activities for balance and mobility.
That doesn't have to mean a gym. Bodyweight exercises at home, gardening or climbing stairs can all play a part. If you're starting from scratch, our piece on starting running gently, from couch to 5k is a kind place to begin, and you can pair it with a couple of short strength sessions each week.
Food is part of the picture too. Our piece on food and mood looks at how eating patterns can show up in your sleep and energy.
If you'd like a second pair of eyes, Thrive Loops lets you share selected information with a participating trainer, health professional or someone you trust. You decide what to share and with whom, and you can change or revoke access at any time.
A kinder way to look at the numbers
Body numbers can carry a lot of weight, in every sense. If they tend to stay with you, try looking at the month rather than the morning, and notice how you feel, how you're sleeping and what you can do now that you couldn't before. Those count as much as any percentage.
If thinking about your body or food feels hard at the moment, it's completely fine to leave these numbers alone for a while and focus on sleep, movement and how you feel. Our piece on when tracking starts to feel stressful has more ideas, and your GP is always a good person to talk to.
Taking it to your GP
Your body composition isn't a diagnosis, and Thrive isn't designed to tell you that something is wrong. If you've noticed changes in your weight or body that you can't explain, or something is simply worrying you, please talk to your GP, whatever any number says.
Where Thrive helps is in getting ready for that conversation in the app. Your trends and history are stored there, so you can open the months you'd like to talk about and show your GP on your phone. Ask Thrive can help you put your questions into words beforehand. Share how you've been feeling and what you've changed in your routine, not just the numbers. Our piece on getting ready for a GP appointment with Ask Thrive walks through it step by step.
Before you buy
You'll need a compatible iPhone or Android phone, because the Thrive app is on the Apple App Store and Google Play, in Australia and eight other countries. The app stores are only for downloading the app, though; they aren't where you buy the Band or a Plan. You can buy at thrivehealthband.com, or at a participating World Gym Australia location or health and wellness clinic.
The Thrive Health Band is A$660 for the first year under the launch offer (usually A$740). That includes the Band, which is yours to keep, and 12 months of the Thrive by Optihealth app, My Health on the web, Health Fingerprint, Ask Thrive, Thrive Loops and your data, paid once upfront. Prices are in AUD and include GST. Free Australia-wide shipping during the launch offer (usually A$14.99).
Nothing renews automatically. After your first year, you can get a new band plus 12 more months for A$660, or keep your band and renew the Thrive Connected Plan for A$240 a year (A$20 a month).
You're also covered by a 12-month Thrive Care Warranty, and consumer guarantees under Australian Consumer Law always apply. See Returns if something is wrong with your purchase.
Common questions
Do I need smart scales to see my body composition?
No. The Thrive Band estimates body fat, lean mass and body water from your wrist using Bio-Z sensing, so there's no separate scale needed. Your results sit in the Thrive app with your other trends.
Why has my body fat reading changed since last time?
Day-to-day changes are normal. Body water shifts with drinks, meals, exercise and the weather, so a single reading can move for ordinary reasons.
Is BMI still worth knowing?
It can be a useful rough guide, and your GP may use it. healthdirect notes that BMI can't tell muscle from fat, which is why looking at body composition over time can add helpful context.
For more answers, see Questions.