Is Your Smart Scale Lying to You?

Feb 4

For decades, we have been stepping on the bathroom scale and letting it tell us our weight, which sometimes also feels a little bit like it is telling us our worth. As scales have gotten smarter, it would appear their feedback about our health is more important than ever. But is it?

The scales of today promise a deeper dive into our health, offering metrics like body fat percentage, muscle mass, water weight, and even bone density. While these features sound impressive, can you trust the $20-$100 scale from Target to give you the reliable data you are looking for? Especially when these metrics start to translate into the way we view ourselves, how much are they helping and when do their inaccuracies start to paint a distorted picture?

Understanding the Data

Smart scales work by using Bioelectrical Impedance Analysis (BIA). When you stand on the scale, a tiny, imperceptible electrical current is sent through your body. Different tissues, like fat, muscle, and bone, have varying levels of water content and thus conduct electricity differently. The scale then uses algorithms to estimate your body composition based on how quickly the current travels.

The Pros:

We are able to take weight beyond just a single metric. Seeing the number on the scale is a good way to track progress over time, but getting more data helps to add more context. Am I seemingly gaining weight because I have transitioned from being chronically dehydrated to regularly well hydrated? Is my weight loss a reflection of fat loss or muscle loss? Getting answers to these types of questions can really help us to hone our dietary behaviors to support complete health. While your weight might not be completely reflective of your hard work, some of these other data points can be. Showing an increase in muscle mass and an overall change in body composition while body weight remains the same can be the exact boost of confidence you need to know that your hard work is paying off.

The Cons:

The metrics you are getting from your scale should be approached with a healthy dose of skepticism, especially when it comes to affordable at-home smart scales. Sophisticated BIA devices used in medical settings can be pretty accurate, but those cost tens of thousands of dollars. Your $100 scale is going to have a pretty large margin of error when it comes to calculating your health metrics. Studies have shown that the accuracy of body fat and muscle mass measurements on at-home BIA scales can vary as much as 10% or more. It is also important to note that these devices are not comparable to each other. If you have a body composition analysis completed at your gym, that does not directly translate to the body composition analysis you are getting from your at-home scale.

Another important distinction is that most individuals are not following proper protocols for measuring body comp when using an at-home scale. When using BIA, we have to account for hydration status, time of day, and recent exercise. So if you have a habit of stepping on your at-home scale at random times throughout the day, those margins of error increase even more. Not only will the data not be accurate, you can’t even trust the trend lines because they are showing your body in varying states.

Understanding the Limitations

If you want to understand the limitations of your at-home smart scale, one of the easiest metrics to look at is bone density. The percentage of error on this metric is as high as 20%, which makes these readings almost meaningless in terms of a health assessment. On a day to day basis, you should not be seeing any changes in your bone mineral density. This is a component that doesn’t change with hydration status or time of day. Your bones are pretty constant. However, many at-home scales will show variability with your bone density measurements depending on the other measurements you receive that day.

I personally have seen a change of 1 pound of bone density calculated within a 7 day period on my at-home scale. 1 pound of bone! Either I am a superhuman with the ability to build bone mass like science has never seen before, or my scale is completely wrong. Considering the total amount of bone calculated for me was 6 pounds, I am going to say it is the latter. Someone who is 5’6 having only 6 pounds of bone mass would need to have hollow bird bones.

So if this scale is using my total weight minus the calculated weight of bone to run its analysis for muscle and fat, how can I trust it knowing my bones likely weigh 3 times that amount? This is where the margin of error and limitations of the scale really come in. All of these numbers need to be used knowing they are likely incorrect, especially when we add in the user error of weighing at various times of day and not always first thing in the morning.

How Can I Use The Numbers?

While you shouldn’t set a goal to be under a certain body fat percentage or hone in on the specific numbers, you can use this as a tool to track progress over time. As long as you are weighing first thing in the morning before eating or drinking, you can use these metrics to note trends. I don’t recommend weighing any more frequently than once a week, and I don’t recommend paying attention to the BIA numbers any more frequently than once a month. If we look at those spaced out data points, we can start to assess trends showing if our body weight and body composition are headed in any specific direction.

We can also use these trends to track hydration status. If your body fat percentage seems to have made a very drastic change in a short period of time that is likely more related to hydration than an actual change in body fat. Assess your water intake and use the feedback from your scale to change hydration habits to maintain more consistency.

Embrace Other Metrics

For too long we have let the scale dictate our health and how we feel. Instead of zoning in on these numbers that may or may not be correct, start assessing other areas of health in conjunction with this data to get a full picture of how you are truly feeling.

Energy levels: Do you wake up feeling refreshed? Or do you chronically feel groggy and fatigued?
Sleep quality: Are you getting consistent restorative sleep? Or are your sleep patterns all over the place?
Fitness levels: Are you making progress with your fitness goals by lifting heavier and running faster? Or have you reached a plateau with your routine?
Feeling in your skin: Are your clothes fitting better? How are you feeling in your own skin?
Dietary habits: Are you nourishing your body with whole, unprocessed foods? Or are you choosing fast foods and ultra processed options that lack fiber and nutrients?

Key Takeaways

Ultimately, a smart scale can be a useful tool for tracking progress overtime. It is important to remember it does have its limitations, especially when it comes to less reliable metrics like bone density. Use it as one piece of information, but don’t forget to check in on all of the other metrics of health.

If you are concerned about bone density, you should speak with your doctor and they might recommend a bone scan. If you notice your mood slipping every time you step on the scale or if you find that you are honed in on a specific number it might be time to ditch the scale and just focus on how you are feeling. Above all, don’t let a hunk of metal be the thing that defines your self worth!