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What's the deal with body fat percentages?

Why look at body fat? What do we need to know about it and how can we use body fat measurements to help us remain healthy?

By checking our body fat readings we can find out how much of our weight is healthy muscle rather than organ-smothering fat. Some tools can even help us gauge where our fat stores lie, although as we can’t control the weight loss from those specific areas this may ultimately be a mixed blessing. Body fat, the amount of fat stored in our body, can seem similar to Body Mass Index (BMI). As healthy body fat percentages for women hover around 18-30% in comparison to BMI of 18-25 many people confuse the two readings but they give very different information. An accurate body fat reading is far more useful than a BMI calculation as it gives insight into what the body mass contains.

Taking regular body fat readings also helps us understand how effective our exercise regimes are. With a well planned training routine it’s possible to gain muscle while losing fat. A kilo of muscle is around a third smaller than a kilo of fat so you may find yourself losing weight slowly even though your belt may now fasten on a tighter notch. In this case, your body fat percentage will have dropped before your BMI reading changes. When you start to understand the change in body composition, in this case the shift in the ratio of fat to muscle, it allows you to make sense of a slow but healthy weight loss. This is often key to keeping you engaged in your health change.

Body fat is difficult to measure. Hospitals have special machines called DEXA scanners and water displacement tools which can read these amounts extremely accurately but the NHS may have more important uses for them than to let you go for a fat measuring field trip.

Many home use weighing scales have a body fat device called bioelectrical impedence analysis (BIA) but readings can waver. There has been much research into the accuracy of this method of testing and most has concluded that BIA results should be interpreted with caution, especially with regards to medical practice. If you already use a BIA device for body fat measurement you can be reasonably sure that even if the reading it gives is not precise it is still effective as a comparison from month to month.

A preferred method for competitive sports trainers is the use of calipers which pinch the skin to measure the fat and allows fat stores to be compared at different parts of the body. Calipers can be purchased for home use and come with all the information required to turn the measurements into a full body fat reading. Taking accurate caliper readings will require a close friend with time on their hands but with practise will give a clear percentage which can be retested regularly. If you are keen to use body fat measurements as part of your health change plan this is a relatively quick and accurate method.

Finally, the US Navy developed the most simple and repeatable body fat measurement system which is done by comparing the size of your neck to your waist and hips. Studies have shown it to be accurate to around 3% when compared to Dexa type body scans used by hospitals. The equation looks a little tricky but there are plenty of calculator websites which will guide you through the process.

So what should your body fat readings be? Here's a table from the American College of Sports Medicine to help you out.

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