Body fat scales

Using an app

Some scales only show readings (except for body weight) via an app. This means you’ll need a WiFi connection and your smartphone handy whenever you want to take a reading. Some models only let you add user profiles via the app too. Using an app allows you to track your results. If the brand has other products, such as blood pressure monitors or fitness bands, you can synchronise the results.

Controls

Do you want to use controls on the scale or on an app. Some models have both options.

User profiles

Make sure there are enough profiles for your household. Depending on the model, user profiles are stored on the scale or on an app.

Display

The display should be big and clear so it’s easy to read when standing on the scales.

Displayed data

The data should be easy to understand and stay on screen long enough to read.

Other measurements

Most models display additional information such as BMI (body mass index), muscle mass, bone mass and the percentage of water in your body. We didn’t test the accuracy of these measurements. BMI is often used by health professionals to assess whether a person is a healthy weight, but this measurement has limitations. It doesn’t consider muscle mass, which is heavier than fat, and can be unreliable for elite athletes, children and some ethnic groups.

Body fat scales let you monitor the effectiveness of lifestyle changes from the comfort of your own home. Even an inaccurate scale, as long as it’s consistent, can let you track whether that extra run or swim a week, or cutting down on the pies and cakes, is making a difference.

But these scales aren’t perfect. Most body fat scales only tell you your overall percentage of body fat, not where you’re storing it. Doctors are more concerned about body fat concentrated around your belly than your hips or legs.

Professor Jeremy Krebs, endocrinologist at the University of Otago’s Department of Medicine said studies show that fat accumulated within or around your organs in your abdomen is more dangerous than that stored under the skin, particularly for diabetes and heart disease.

“A further caution is the technology depends on the current transmission through water. This means your level of hydration and even moisture on your feet can affect the measurement. This makes comparing results on different days difficult if you’re tracking your body fat over time,” Professor Krebs said.

These scales also aren’t suitable for everyone. Readings may be unreliable for children, athletes and bodybuilders. Our test found results were also fickle for people with very petite or large builds.

Body fat scales shouldn’t be used by pregnant women or people with metal screws or plates in their body. If you have a pacemaker, check with your doctor before using one – the scale’s electrical current could interfere with it.

None of the scales we’ve tested measured body fat accurately enough to recommend. All models tended to under-read body fat compared with the DXA scan, so your actual fat percentage will be higher. This means if your actual body fat is 25 percent, the scale may read it as only 21 percent.

Body fat scales send a very low electrical current through your body via your feet. Tissue containing a lot of water, such as muscle, lets the current through easily, but fat, which contains comparatively little water, resists the current. The more fat you have, the higher the resistance.

The scales then use an algorithm that uses the resistance data along with information such as your gender, age, height and level of fitness to calculate your body fat percentage. You enter this information directly into the scale or via an app.