Just how helpful are fat monitors? (2024)

Sales of traditional bathroom scales have dropped as slimmers switch to hightech body fat monitors. These devices not only tell you how much you weigh, but also reveal what percentage of your body is pure fat.

It's an important step forward in health terms, as it's excess fat rather than weight that is the problem. When you step on a set of scales, you're not just weighing fat, but also muscles and bones.

In contrast, a body fat monitor allows you to measure just how much fat is in your body, giving a much truer picture of how overweight you really are.

About half the adult English population is overweight or obese, which increases the risk of diseases such as diabetes, heart disease, stroke and cancer.

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A healthy body fat percentage for a woman of 20-39 years is 22-36 per cent, and for a man it's eight to 20 per cent. But as body alters with age, we lose lean tissue. So even if you weigh the same at 40 as you did at 20, the chances are your body will be fatter.

You can reverse this with diet and exercise - and body fat monitors will help you, says Dr Frankie Phillips of the British Dietetic Association.

"It's a good motivational tool for someone who has been dieting and exercising and is starting to lose motivation because nothing is changing on the scales."

Body fat used to be measured using callipers, but today's devices are more sophisticated, and rely on a high-tech method called BIA (bio-electrical impedance analysis).

Most are similar to normal scales - you stand on them in bare feet - others are hand-held. The monitor passes a low-level, imperceptible electric current through your body. Lean tissue contains mainly water (73 per cent) and electrolytes, which conduct this current.

Fat, however, contains no water and is not a good conductor, so it impedes the current. By measuring your lean body mass, the monitor can predict your fat mass.

For best results, the monitors should be used at the same time of day, once a week. Wear minimal clothing. You need to empty your bladder before use, as this will affect the results - avoid alcohol and using the device straight after exercising.

A good device will not only be accurate in its readings, but consistent - so you can keep track of any changes in fat percentage. There are a number of models available.

Some which measure not just body fat but even visceral fat (the dangerous fat around the organs linked to heart disease). But are they any good?

We asked Joanna Seager, 31, to put eight to the test. First, obesity researcher Dr David McCarthy, from the Institute for Health Research at London Metropolitan University measured Joanna's body fat using a highly accurate scientific scanner called a BodPod (pictured right) - it measures the volume of air you displace while sitting inside the pod.

Joanna is 5ft 5in and weighs 10st 12lb - her body fat reading is 27.8 per cent.

So how did High Street products compare?

Here Dr McCarthy provides his expert verdict.

OMRON BF500

Body Composition Monitor, £99.95 (available from July)

WHAT IT MEASURES:

Visceral fat, resting metabolism (the daily calories you need) and skeletal muscle percentage (proportion of your body made up of muscles attached to bones), as well as calculating your BMI.

HOW TO USE: Simple to programme. Stand on monitor, pull up a handle and hold it at right angles to the body.

READING:31.4 per cent