How Accurate Are Body Fat Scales?
Body fat scales provide a rough estimate of your body composition based on your weight and other factors. However, research suggests that smart scales may not be fully accurate at measuring body fat.
Various factors can affect your overall weight. For example, increased muscle mass can make the number on the scale stay the same or, in some cases, increase, even if you're losing fat and becoming more toned.
Therefore, you may be more interested in learning about your overall body composition than your weight. Body composition refers to the amounts of bone, fat, muscle, and other tissues in your body. Healthy body composition goals vary from person to person.
Smart scales are commercially available tools that claim to measure body fat and overall body composition.
Even if you're not trying to lose weight, a body fat scale may help you determine whether you have an optimal fat-to-muscle ratio.
Body fat scales aren't foolproof, and some research suggests they lack accuracy. However, you may still want to use one in between visits with your doctor or personal trainer.
You'll notice the language used to share stats and other data points is pretty binary, fluctuating between the use of 'male' and 'female' or 'men' and 'women.' While we typically avoid language like this, specificity is key when reporting on research participants and clinical findings.
How do body fat scales work?
Body fat scales are easy to use. You simply step on the scale, and the tool measures your body composition. According to a 2023 review, smart body composition scales can measure:
muscle mass
bone mass
water weight
visceral fat, which is fat around the abdomen
These scales have sensors underneath your feet that use bioelectrical impedance. Bioelectrical impedance uses a weak electrical current to measure the amount of resistance from body fat.
When you step on the scale, the current runs up through your leg and across your pelvis. Then, the sensors in the scale measure the level of resistance that the current meets as it travels back through your other leg.
Depending on the type of body fat scale you have, the information can link up to your smartphone or smartwatch, as well as any fitness apps you might have.
As a rule of thumb, greater body resistance means a higher fat percentage. Fat contains less water than muscle, so it's more difficult for a current to travel through it.
Are body fat scales accurate?
According to a 2021 observational study, body composition scales are reasonably accurate at measuring total body weight but not body composition. Possible reasons for this include:
the size and width of a person's feet affecting the measurement
a lack of guidance on where to put the feet
changes in body positioning
A 2023 review highlights that moving before the scale finishes measuring could lead to errors or missing data. The review's authors also caution that manufacturers of smart scales may not be fully transparent when marketing their scales.
This means you may experience inaccurate results or measurements that don't quite align with the product's claims.
These scales also cannot consider certain important factors, such as a person's age.
Ultimately, commercial body composition scales are not as accurate as professional measurements, which may use imaging tools such as X-ray to measure your body fat.
What are the pros and cons of body fat scales?
The greatest benefit to using this type of scale is that you can measure your body fat in the comfort of your own home at any time, all without traveling to a gym or clinic.
However, these scales aren't completely accurate, so you may not want to rely on them alone to measure your overall health.
Another drawback is that a body fat scale doesn't take into account other variables of body fat, such as where you might have it.
For example, doctors tend to be more concerned about body fat around your midsection because this can increase your risk for certain health conditions, like hypertension, diabetes, and heart disease.
Even if the measurement is accurate, a body composition scale can only tell you the overall fat percentage and not where on the body you're storing potentially dangerous fat.
Body fat vs. BMI
Body mass index (BMI) is another way to assess your body composition. While BMI can't measure fat or distinguish it from muscle and bone, it does provide an overall picture of whether you're in a suitable weight range for your height and age.
The Centers for Disease Control and Prevention (CDC) outlines the following BMI recommendations for adults:
You can use online calculators to determine your BMI, such as this one from the National Heart, Lung, and Blood Institute.
The downside to relying on BMI is that it doesn't measure body fat. So, an athlete with a lot of muscle, for example, could have a higher BMI based on their weight and height.
The CDC highlights that other indicators of health are just as important to consider as your BMI, including:
underlying health conditions
health and lifestyle habits
findings from physical or laboratory exams
Other ways to measure body fat
While stepping on a scale is perhaps the easiest method of body fat measurement, there are other ways you can determine your body fat percentage. Aside from BMI, you can ask a healthcare professional about the following methods:
Waist measurements
One drawback to body fat scales is that they don't tell you how much fat your body holds around the waistline. Research shows that visceral fat increases your risk of issues such as:
cardiovascular diseases
type 2 diabetes
high cholesterol
Measuring your waistline can help complement body fat scale results.
The National Heart, Lung and Blood Institute notes that the risk for heart disease and diabetes increases if you are a woman with a waist measurement greater than 35 inches (88.9 cm) or a man with a waist measurement of more than 40 inches (101.6 cm).
Calipers
Many fitness professionals use calipers. These tools pinch your skin folds (usually around the waist or hips) to estimate your body fat.
The accuracy of this method varies. The results may be more or less accurate depending on factors such as the expertise of the person taking the measurement.
Dual-energy x-ray absorptiometry (DEXA) scans
Often used to measure bone mass for osteoporosis diagnoses, DEXA scans are also reliable methods of body fat measurement and can be more reliable than relying on BMI alone.
You'll need to find a center with the equipment to get one of these scans. They can be pricey depending on your location, and insurance does not always cover them.
Handheld fat measurement devices
This body fat measurement test works similar to that of a scale, except it doesn't measure your weight. There are sensors on either side of the device that measure your body fat as you hold the device in front of you.
Handheld fat measurement devices tend to use bioelectrical impedance, like smart scales. This means they may not be as accurate as other methods that professionals use, but they're easy to use at home and relatively inexpensive.
Underwater weight (hydrodensitometry) test
Fat floats more easily than muscle. The person administering the test calculates your body fat percentage using your total body weight and buoyancy.
According to a 2018 review, underwater testing is an accurate tool to measure body fat. However, it can be difficult to find a center that can perform this type of testing. Some people may also find the test uncomfortable.
Bod Pod
Available at some fitness centers and medical facilities, a Bod Pod is a device you sit in for a few minutes while it measures your body fat via air displacement plethysmography (ADP).
This method has similar accuracy to underwater testing. However, access to these devices is limited, and testing can be expensive.
Takeaway
Body fat scales can be helpful when you're trying to measure your body fat, but they don't tell the whole story about your fat-to-muscle ratio. Instead, you can use these scales as complements to other tools.
When using body composition scales, it may help to use the same set of scales each time and use them at the same time every day you measure yourself.
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