Can Smart Scales Accurately Assess Body Fat Mass?

Smart scales can help estimate the amount of fat in the body, but they do so inaccurately. All they are capable of is showing whether a person is losing or gaining fat. Although it is possible to monitor body weight without smart scales, research shows that such devices can help some people maintain motivation for weight loss.

How Smart Scales Work

What are smart scales?

Smart scales combine standard electronic scales with a bioelectrical impedance analysis device to evaluate the contribution of fat, muscle, and bones to body composition.

How does bioelectrical impedance work in smart scales?

The smart scale platform contains four electrodes that pass a very weak electrical current through a barefoot person’s body. The current goes up one leg, passes through the pelvis, and down the other leg.

Muscles conduct current effectively because they contain a lot of free water with dissolved electrolytes. Tissues with low levels of free water, such as fat and bone, conduct current poorly. The scales take this difference into account and use special formulas to calculate the mass of fat tissue in the body. Some scale models also calculate the amount of muscle and bone tissue.

How accurate are smart scales?

The companies that manufacture smart scales organize most of the research on them, and there are not enough participants in independent studies to draw definitive conclusions. French scientists published the largest independent study on the accuracy of smart scales in 2021. They examined scales from three brands: Body Partner, DietPack, and Body Cardio.

The researchers divided 153 adult volunteers into three groups and measured their body weight and body fat mass in the laboratory using densitometry, which is considered the gold standard for measuring bone density and other body components. After that, they used one of the smart scale brands to measure the volunteers’ body weight and body fat mass and compared the results. Here’s what they found out.

Accuracy of body weight measurement

All three smart scale brands had an average absolute error that did not go beyond 0.3 kilograms, which meets the standard requirements for electronic scales that should not exceed an error of 0.5 kilograms.

Accuracy of body fat measurement

The three smart scale brands consistently produced similar results when the same volunteer stood on the scales repeatedly. However, the tested devices underestimated body fat mass significantly: Body Partner underestimated by 2.2 kilograms, Body Cardio by 3.7 kilograms, and DietPack by 4.4 kilograms. Earlier studies with fewer participants also reported similar results, showing that smart scales tend to underestimate body fat mass.

From the available data on smart scales, it seems that these devices may only benefit people who weigh themselves several times a week. This approach helps to gather statistics and determine whether an individual is losing or gaining fat. However, if a person weighs themselves once a week or less, there will be no benefit as smart scales do not provide an accurate reflection of the body’s composition.

Why fat measurement accuracy low with smart scales

The design of the scales is likely the issue since the electrodes integrated into them only gather information on the lower body, and the formulas used to calculate the fat content in the upper body consider the typical distribution of adipose tissue in the human body, factoring in age, gender, weight, and height.

The scale manufacturer typically substitutes formula data with the body composition of a typical resident of their region. However, the average Korean or Chinese body composition may differ significantly from that of an average American or Russian. Therefore, even if scales are purchased from the same region, accurate calculations are not guaranteed due to the significant differences between real individuals and average values.

To solve this issue, designers can create a bioimpedance device that measures fat mass in both the upper and lower body. Such devices already exist as medical analyzers of body composition. They have two pairs of electrodes – one for the legs and another for the hands – and can collect information on the entire body’s fat content for more accurate results. However, smart scales that can measure both upper and lower body fat, muscle, and bone content have not yet been developed.

Is it worth buying smart scales?

Smart scales are not included in the list of devices necessary for weight control. But some studies show that people who use such scales lose weight slightly faster than those who use regular ones.

Why you can do without smart scales

People who are healthy and not engaged in professional sports can successfully monitor their weight dynamics by relying on two key indicators: body mass index (BMI) and waist circumference.

Calculating BMI only requires knowing your height in meters and weight in kilograms, and regular electronic scales are just as good as smart scales at displaying body weight. You can calculate BMI by dividing weight in kilograms by height in meters squared, or by using an online BMI calculator and entering your data.

A healthy weight is considered if BMI falls within 18.5-24.9. Overweight is defined as a value within 25-30, while a value exceeding 30 is considered as obesity. Most scientists and doctors suggest considering weight control when overweight to reduce the risk of developing obesity and related chronic diseases.

Waist circumference determines the amount of fat surrounding internal organs, making it the second important indicator. The higher the amount of such fat in the body, the greater the risk of developing type 2 diabetes and cardiovascular diseases.

Evaluating this parameter using smart scales is useless, as they only show the total body fat content, including that under the skin. Instead, a simple but reliable way to estimate visceral fat content is to measure the waist with a centimeter tape. If a man’s waist circumference exceeds 102 centimeters or a woman’s exceeds 89 centimeters, their risk of obesity increases.

The effectiveness of smart scales as a weight loss tool has little data. A 2017 study shows that people who followed the same weight loss program but used conventional weights lost more than 5% weight three months earlier than those who used smart scales. However, both groups lost the same amount of weight at the end of the six-month study.

Smart scales may indicate a decrease in body fat, which could explain the faster weight loss. However, motivation may also play a role in a person’s adherence to a balanced diet and continued exercise, even when they do not feel like it.

Smart scales have a few other important factors to consider. Any bioimpedance-based device is highly sensitive to even the slightest variations in water levels. For example, if a person weighs themselves after an intense workout during which they sweat a lot, their scales will show an increase in adipose tissue on the body.

Weighing oneself at the same time every day, such as before breakfast or after a trip to the bathroom, is the best way to avoid confusion with smart scales. Obtaining results at the same time ensures greater reliability.