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Should You Trust the Reading You Get from Body Fat Scales?

Body Fat Scales

 

Body fat scales are popular these days, especially among bodybuilders and people who exercise. A standard scale gives you your total body weight but says nothing about your body composition. Your total body weight comes from muscle, fat, bone tissue, and water weight. If you lose a few pounds, you hope it’s body fat, but there’s no way to know with a standard scale. That’s why body fat scales are growing in popularity.

A body fat scale measures your body weight, but also tells you your body fat percentage using bioelectrical impedance. When you stand on a body-weight scale, the scale sends a low-energy electrical current that travels up one leg and down the other. Based on how quickly the current moves, the scale calculates your body fat percentage. It can do this because the electrical current moves faster through fat than through muscle.

Unfortunately, these scales have limitations. One of the biggest is that body fat scales are sensitive to how well hydrated you are. If you’ve been drinking lots of fluid and are even a bit overhydrated, the scale can give you a falsely low body fat percentage reading. Likewise, if you’re dehydrated, it will overestimate your body fat percentage.

This is What Body Fat Scales Are Most Useful For

Body fat scales have limitations if you’re looking for an absolute reading of your body fat percentage. What they are useful for is monitoring for changes in body fat percentage. The key is to step on the scale first thing in the morning after urinating, so the conditions are standardized. When you wake up in the morning, you haven’t eaten a meal or drunk water for a significant time.

If you record first morning readings each morning, you can see whether the values are going up or down. This will give you a better idea of how your body fat percentage is trending. Still, it’s not an absolute measure of body fat.

Even if you measure your body fat percentage first thing in the morning, the value could be off if you ate a substantial meal the night before, especially if it contained lots of salt. If you’re female, where you are in your menstrual cycle can also affect the readings. By keeping a record of the measurements, you can see how the values vary at different times of the month.

So, don’t use the scale as the be-all-end-all for your body fat measurements. It’s best for picking up trends and changes, rather than absolute values. You can also use a body fat scale in conjunction with skin calipers for more accuracy.

More Accurate Ways to Measure Body Fat

The biggest thing body fat scales have going for them is convenience and accessibility. The gold standard for measuring body fat percentage is called a DXA scan. You might be familiar with DXA scans since they’re also used to measure bone density. But you must go to a center that offers this test, and you will be exposed to a small dose of radiation. So, it’s not practical for monitoring changes in your body fat percentage.

There are other ways to measure body fat percentage, like hydrostatic weighing. For this method, you get into a water tank, and a technician determines how much water your body displaces in the tank. They can extrapolate your body fat percentage from that. Still, it’s not a test you can do at home or one you can use to follow your body fat percentage on a week-by-week basis.

There’s also a technique called the Bod Pod that some gyms offer. It’s like hydrostatic weighing, except you get into an air-filled chamber. The technician alters the air pressure in the chamber and calculates your body fat percentage based on the relationship between volume and air pressure within the pod. It’s a fairly accurate way to measure body fat percentage but can be expensive.

Calipers for Measuring Body Fat Percentage

Investing in a pair of calipers is the least expensive way to measure your body fat percentage, but it takes more skill than stepping on a scale, and accuracy depends on how experienced you are. If a well-trained person does the measurement, body fat percentage measurement errors can range from 3.5% to 5%.

Calipers measure subcutaneous fat, the fat underneath the skin, not body fat as a whole. There are two types of calipers: mechanical and digital.

Mechanical calipers use a sliding mechanism and measure the thickness of the skin. Digital models are comparable to mechanical models, except they have a digital readout.

The best part about caliper measurements is they are quick and easy to do, and you don’t need special machines. Just make sure you get a caliper that measures in millimeters, not inches, if you want an accurate reading.

Calipers aren’t as accurate as other methods and can be hard to read if you’re not used to doing it. You’ll also need to measure skin thickness at seven sites and average them together to get an accurate reading.

The Bottom Line

Body fat scales can’t tell you your absolute body fat percentage, but they are a simple way to follow changes in your body fat percentage over time. The cons are their lack of absolute accuracy and the fact that they cost between $50.00 and $100.00. However, that’s a lot less than the cost of a DXA scan or hydrostatic weighing. It might be worth it if you’re trying to determine how your body fat percentage changes over time and aren’t looking for a highly accurate measurement of body fat percentage.

References:

  • Biomed Res Int. 2014; 2014: 475659.
  • Body composition (Lukaski) Body composition : health and performance in exercise and sport / edited by Henry C. Lukaski. Boca Raton : CRC Press/Taylor & Francis Group, 2017.
  • Nutrition in Clinical Practice, vol. 19, no. 5, pp. 443-446, 2004.
  • “DXA/DEXA beats BMI: Using an X-ray Exam to Measure Body ….” 29 Oct. 2015, radiology.ucsf.edu/blog/dxadexa-beats-bmi-using-x-ray-exam-measure-body-composition-fat-loss.
  • “How to measure body fat: Accurate methods and ranges.” 12 Sept. 2019, medicalnewstoday.com/articles/326331.
  • Wells JC, Fewtrell MS. Measuring body composition. Arch Dis Child. 2006;91(7):612-617. doi:10.1136/adc.2005.085522..

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