Let’s talk about fat.

As a Personal Trainer in Pasadena CA I often have to explain to my new clients the meaning behind an individual’s body fat measurement.  So lets talk about fat.

More specifically, let’s talk about the BMI (Body Mass Index). You’ve probably seen a chart of it somewhere: weight on one axis, height on the other. You match up your measurements and find the number that goes with it, and it tells you how “fat” you are. Pretty straightforward, right?


A BMI value of over 30 is considered “obese.” But it doesn’t take into account where your weight comes from – that is, what % of your weight comes from fat. Many athletes classify as overweight or obese in spite of their low body fat percentage, because muscle is denser than fat (so you can pack more mass into the same amount of space). And an individual who lives a very sedentary lifestyle (and therefore low muscle mass) might really be obese but the BMI value would be too low. It was designed to study populations, not individuals. We’re too varied in build for the Body Mass Index to be used by a person who isn’t exactly average.

So let’s use a metric that is more accurate you’ve probably also heard about: Body Fat Percentage (BF%). All it is a ratio of fat in your body to everything else (muscle, bone, etc.). Some fat in your body is actually essential for you to be able to live – it provides protection for your organs, it serves as energy storage, and your brain is mostly made out of it (60%)!

Here’s a basic BF% chart from the American Council on Exercise – note that the values are different for men and women because women naturally have higher fat content (because they’re biologically responsible for having to nourish a growing fetus at some point in their lives, whether or not they want to).

Men Women
“essential fat” 2% – 5% 10% – 13%
“athletes” 6% – 13% 14% – 20%
“fitness” 14% – 17% 21% – 24%
“acceptable” 18% – 24% 25% – 31%
“obese” 25% and higher 32% and higher

“Essential fat” means that absolute minimum for your body to function. A woman at an “essential” level can actually stop menstruating, because her body knows it doesn’t have the energy storage to provide a baby if she were to get pregnant.

If you’re looking for that “ripped” look – aim for the “athletes” percentage range. If you’re just looking to be healthy, the “fitness” or lower percentages in “acceptable” are good targets to aim for. (Note that this chart doesn’t take into account muscle mass, so two people with the same percentage of body fat could have completely different physiques.)

So, how does one measure their BF%? There are several methods of varying levels of accuracy and cost. The simplest (and cheapest) is just to do it by eye. Take photos of yourself and compare them to those on the internet (be wary that the percentages touted are correct, though – maybe check out the photos here.)

If you want to actually take some measurements, you can buy calipers. They’re fairly cheap, and give an estimate of your BF% by pinching various parts of your body. The accuracy depends on the number of data points you give it. If you only take a measurement, say, on your stomach, and that’s where you carry most of your fat, you’re going to get an overestimated BF%. Other measurement styles and calculators online are based off of waist size, and again, tend to be less accurate than the more expensive methods outlined below.

You can buy a body fat scale or monitor that measures the amount of electric current that goes through your body. It’s called Bioelectrical Impedance Analysis and is based off the fact that different tissues in your body have different resistances to current flow. Electricity flows faster through muscle, slower through fat, and by measuring the total resistance with your weight can estimate the percentage of fat you have. It sounds super sciency, but can be easily thrown off by the amount of water you’re carrying or how recently you ate. Also, Consumer Reports tested various models and found them all to be inaccurate.

Then there’s displacement methods – both your weight and your volume are measured (the latter based on how much air or water your body displaces, hence the name) to get a density and, knowing the densities of fat and fat-free mass, derive a fat percentage value. They’re more accurate than the above methods, but studies still show they’re not perfect. They’re also relatively expensive.

Similarly costly is DEXA (Dual Energy X-ray Absorbtiometry) Scanning. It’s more accurate in that it differentiates beyond fat and not fat that the displacement methods do. It was originally designed as a bone-density scan, and so it sorts your body mass into 3 categories – bone, fat, and “other” (including muscle). It can also estimate the body composition of sections of your body, and not just give you a number for the whole thing. But (and there’s always a but) there are still errors in the tech just like above, and some studies show it to be no better on an individual level than the water displacement method. This site actually has a lot of links to studies for the various methods of finding BF% and how inaccurate they can be.

To summarize, no method is perfect. Focus more on consistent loss of body fat than the actual numbers these methods spit out.

So how do I decrease my BF%? Here’s a few tips:

Consume fewer calories than you burn, and limit the carb intake. (Note that if you aren’t strength training/lifting heavy you’re probably going to lose muscle mass as well as fat, so keep up the exercise regimen at the same time!) Strength training – as well as sprinting – also helps lower body fat by making your body continue to burn calories after you work out. Eating fewer carbohydrates will force your body to access its fat reserves. Maybe try your hand at a quasi-Paleo diet.

Remember, the lower your body percentage is starting off at, the more strict your diet and exercise regimen will have to be to see a change. But don’t drop too low or you’ll actually harm your body. “Too much” fat is bad. But no fat can be even worse.

Use the BF% as a guideline to keep your body and fat-filled brain happy and healthy.

By: Pasadena Personal Trainer Ron Le
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