The extra pages that come with your REMS bone scan — what they measure, what they don’t, and why “low” doesn’t mean “wrong”.
If you have had a REMS bone scan, you may have been handed a second report full of figures: fat mass, muscle, body water, visceral fat, a metabolic rate, even an “estimated biological age”. It looks impressive. This guide explains what it genuinely tells you, what it cannot tell you, and why some perfectly healthy people are surprised to find themselves labelled “low” or “high”.
Your REMS scan measures one thing about your body composition: roughly what proportion of you is fat.
When the ultrasound probe passes over your lower back and abdomen to look at your spine, the sound waves have to travel through fat and muscle to get there. The way the sound is slowed, scattered and reflected on that journey is slightly different depending on how much fat is in the way. The software listens to that difference and turns it into a single estimate: your body fat percentage.
That is the measurement. It is a real one, and it costs you nothing extra — you were having the bone scan anyway.
Everything else on the report is worked out with a calculator. Your height and weight were typed in when you arrived. Once the machine has your body fat percentage, it can multiply, subtract and estimate its way to all the other figures:
Your scan measured your body fat percentage. Every other number on the report was calculated from that figure, plus the height and weight you gave at reception. They are not six separate discoveries about you. They are one measurement, presented six different ways.
This is the question that causes the most unnecessary worry, so it is worth being very clear.
The report compares you with other people of your age and sex — not with a standard of good health. Those are two completely different things.
Take a real example. A fit, well 68-year-old woman weighing 8 stone 7 lb (119 lb / 54 kg) at 5′5″ had a REMS scan. Her body fat came out at 31.5%. The report flagged this as LOW, because the “standard” range printed on her page was 35% to 45%.
But that range simply describes what is typical for women of her age today. Many women in their sixties and seventies carry a good deal of body fat and rather little muscle. Her report was, in effect, telling her: you have less body fat than the average woman of your age.
That is not a problem. In her case, it is a good thing. Around 31% body fat sits comfortably within the healthy range for a woman of her age. She was not fat-deficient. She was simply healthier than the average — and the machine, which only knows how to compare her with the average, called that “low”.
If your report says your fat is “low” and your muscle is “high”, these are not two findings — they are the same finding said twice. Your fat and your muscle have to add up to your weight, and your weight was measured on a scale. So if the machine decides you have less fat than average, it must automatically conclude you have more muscle than average. It has no choice: it is arithmetic, not a second discovery. Nobody should be advised to gain body fat on the strength of one of these reports.
| On your report | How much weight to give it |
|---|---|
| Body fat percentage | Reasonably useful. A broad estimate of how much of you is fat. Think of it as a good ballpark figure, not a precise one. |
| BMI | Genuinely useful — and it needs no scan at all. For bone health in particular, a low BMI matters (see below). |
| Fat mass and fat-free mass | Calculated from the two above. They add nothing new. |
| Basal metabolism (calories) | Treat as a rough guide only. Different accepted formulas can disagree by 200+ calories a day for the same person. Never plan a diet around the exact figure. |
| Activity metabolism figures | Your basal figure multiplied by a standard number. Your actual activity was not measured. |
| Body water, proteins and minerals | Best ignored. These have not been independently validated for this device. |
| Visceral fat level | An in-house score, not a measurement in any standard unit. Interesting, unproven. |
| Body type box (“athletic”, “low fat muscular”…) | A label based on where you fall on a grid. Gaining or losing a kilo could move you to a different box. |
| Estimated biological age | Not a health finding. The manufacturer’s own small print says it is there “for the motivation of the subject”. Enjoy it if it is flattering; do not act on it. |
For the 68-year-old woman above, one figure on her body composition report deserved a proper conversation with her doctor — and it was not one that came from the ultrasound at all.
Her BMI was 19.8. That is at the very bottom of the normal range. After the menopause, being light and slightly built is one of the recognised risk factors for thinning bones and for breaking a bone if you fall. It is one of the factors doctors feed into formal fracture-risk calculations.
So the most valuable thing her body composition report did was to put a number in front of her that prompted the right conversation: given that I am slim and post-menopausal, what should I be doing about my bones? The answers there are the familiar, powerful ones — enough protein, enough calcium and vitamin D, and above all resistance training, which builds both the muscle and the bone that a light frame needs.
You may have used a bathroom scale, a gym machine or a clinic device that measures body composition by passing a tiny, harmless electrical current through you. This is called bioelectrical impedance analysis, or BIA.
The honest answer is that the two methods are close cousins, and neither is a precise measurement.
In fact, when the REMS body composition feature was developed, it was tested by checking whether it gave similar answers to a BIA machine. That was the yardstick. So it is not surprising that the two agree — and it means REMS cannot really claim to be more accurate than BIA, because BIA is what it was taught to copy.
| REMS (your ultrasound scan) | BIA (electrical current) | |
|---|---|---|
| The big advantage | It is free — it comes with a bone scan you were already having. And it is not upset by how much you have had to drink. | Long track record, widely available, and can estimate arms and legs separately. |
| The big drawback | Very little published research behind it, and no published figure for how much it wobbles between scans. | Results shift with hydration — a big drink, a heavy meal, a workout or swollen ankles can all change your reading. |
| Preparation needed | None. | Usually fasting, no recent exercise, standardised timing. |
| Can it check for muscle loss (sarcopenia)? | No. | Partly — but a DXA scan and a strength test are what is really needed. |
If you need a properly detailed picture of your muscle and fat — because of unexplained weight loss, frailty, cancer treatment, or a serious question about muscle loss — neither of these is the right tool. A DXA scan can measure fat and muscle region by region, and your doctor can add simple strength and walking tests. That combination is the standard.
An important limit you should know about: the body composition part of the REMS system is approved as a wellness tool for generally healthy adults. Its official approval states plainly that it is not for diagnosing any disease or condition. That is not a scandal — it is simply what it is. But it does mean that no diagnosis of obesity, muscle loss or malnutrition should ever rest on these pages alone.
Your report may include a “Follow-Up” chart, ready to plot your figures at each visit. It is tempting to watch it closely.
Be careful. Every measuring device has a certain amount of natural wobble, and before you can say a change is real, you need to know how big that wobble is. For the bone part of the REMS scan, that figure has been published. For the body composition part, it has not.
In practical terms: if your body fat reads 31.5% today and 32.4% next year, nobody can currently tell you whether you have genuinely changed, or whether the probe simply sat a centimetre differently. Do not let a small movement on that chart worry you — or reassure you.
Your REMS body composition report measures one thing — roughly how much of you is fat. Everything else on the page is calculated from that figure and from your height and weight. It compares you with other people your age, not with a picture of good health. If it calls your body fat “low” and your muscle “high”, that usually means you are doing better than your peers, not that something is wrong. It is a free, rough, useful snapshot — and a good conversation-starter. It is not a diagnosis, it cannot detect muscle loss, and it should not be used to decide that you need to gain weight or fat. The most valuable number on it is often the simplest: your BMI. If it is low and you are past the menopause, that is worth a proper conversation about your bones.
This guide has been produced by the Education Directorate of IIMHE and is based on the manufacturer’s regulatory documents, the published research on REMS and on bioelectrical impedance, and a direct analysis of a real EchoStudio v2.3 report. It is general information and is not a substitute for advice from your own clinician, who knows your full history. A companion Critical Analysis, with full references, is available for professional readers.
2nd February 2026 @ 20:00 GMT
Nutrition and musculoskeletal health
Given by: Dr Kimberley Zambito, Orthopaedic Consultant
Hosted by: Dr Nick Birch
Throughout 2026 and beyond, IIMHE (the International Institute of Musculoskeletal Health Education), in partnership with OsteoscanUK, will host a series of engaging educational webinars, open to anyone interested in bone and musculoskeletal health.
