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Body Fat Percentage: What is it?

Although many of us understand the importance of body composition compared to the number on the scale, for many of us, the intricacies of body fat percentages and how they are calculated also remain confusing.

Here is a quick-start guide to help you understand what body fat is

as a percentage and how it relates to your goals.

Key Takeaways

  • Body fat percentage represents your fat mass, divided by your total body weight.

  • Body fat percentage is an essential benchmark for progress because we want to retain as much lean body mass as possible during a diet.

  • To prevent overestimating how many calories you need, we calculate energy requirements based on lean body mass rather than total body weight.

  • We calculate protein based on lean body mass to fuel muscle tissue, not fat.

  • All forms of body composition analysis come with flaws and should therefore be used as a benchmark for progress and not regarded as an absolute number.

What is body fat percentage?

Your body fat percentage is the weight of all the fat on your body (fat mass) divided by your total body weight. For example, if you weigh 176lbs and have 22lbs of body fat; your body fat percentage is 12.5%.

Why measure your body fat percentage?

Measuring your body fat percentage allows you to track your fat loss progress over time. You can also use it to calculate how much lean body mass (LBM) you have, which is the total weight of your body minus all your fat mass.

A common misunderstanding is that LBM only refers to muscle when it describes everything apart from body fat. So, in addition to muscle, it also includes your organs, bones, skin, body water, and food weight.

When creating a meal plan, I have pattened software that calculates your daily targets based on how much LBM you have, rather than total body weight.

This distinction is essential because body fat and LBM do not have the same energy or nutrient requirements. For example, each day, your body burns roughly 12 kCal per pound, maintaining its current amount of LBM.

In contrast, although your fat cells are more than just passive storage sites for fat and perform several essential functions, like hormone production, they have a relatively low maintenance cost of 2 kCal per pound.

If you are relatively lean, this is not really an issue. For example, if you weigh 80kg and have 10% body fat, whether you decide to use 176lbs or 158lbs (your LBM) to create your meal plan will not make a big difference.

However, if you carry a lot more body fat (upwards of 30%), calculating your calorie

requirements based on your total body weight will overestimate how many calories you need.

This also applies to other nutrition targets that I tend to set relative to body weight, such as protein. The primary role of protein is structural, which means that your body uses it to build and repair components of your LBM, such as muscle. As a result, it makes sense to set your protein target relative to how much LBM you have rather than body fat, which does not require large amounts of protein.

How to measure your body fat percentage?

The only way to directly measure your body fat is via cadaver analysis (dissection of a dead human body), which has some obvious

practical limitations.

All other methods of body fat testing only estimate how much body fat you have. Each body fat assessment tool is based on a a different set of assumptions, and you cannot compare your results between them.

Skinfold caliper testing

The skinfold caliper technique is based on the assumption that there is a relationship between the thickness of skinfolds (which includes the 'pinchable' subcutaneous fat beneath your skin) at various sites around your body and your total body fat.

Of all the available options, skinfold testing is the most cost-effective and practical body fat assessment method available to personal trainers. The primary limitation of skinfold calipers is that measurement reliability depends on the skill and experience level of the operator.

Measuring just 1cm away from a defined measurement site produces significant differences in measurement values. As a result, I do not recommend using skinfold testing unless you have access to a personal trainer who has relevant qualifications and experience taking measurements.

High-tech methods

Two examples of more high-tech options are dual-energy X-ray absorptiometry (DXA) and hydrostatic weighing. A DXA scan is a special type of X-ray that

sends low-dose X-rays through your body and measures the absorption rates of different body tissues. The rationale is that body fat and LBM has different absorption properties, which allows them to be isolated and measured.

Hydrostatic weighing (also known as underwater weighing) involves comparing your dry weight on land to your underwater weight. Components of LBM like bone and muscle are denser than water, whereas fat is less dense.

As a result, if two people weigh the same on dry land, but one has more body fat, the fatter person will weigh less underwater. Put simply, fat floats and muscle sinks!

While DXA and hydrostatic weighing may be more accurate than some low-tech options, they are expensive and impractical (require you to visit a research laboratory or clinic) to create a meal plan and monitoring short-term changes in your body composition.

However, DXA scans can be helpful at the start and end of your transformation if you want to learn more about your body composition.

Bathroom scales

Bioelectrical impedance (BIA) is the technical name for the technology found in body weight scales that also estimate your body fat percentage. It works by sending a small electrical signal through your body and measuring the

resistance of different body tissues to the signal.

The scale then estimates your body fat percentage because the current flows more easily through parts of your body that have a high water content (e.g. muscle and blood) than it does those with low water content (e.g. bone or fat).

A big problem with BlA devices is that they are susceptible to changes in your body's water balance. Exercise, food, drink, and whether or not you have been to the toilet can all affect the reliability of your results.

Overall, there is limited research to support the accuracy of consumer-grade devices, so I recommend only using your scales to weigh yourself.

Tape measurements

The tape measurement method involves measuring the circumference of various sites around your body and inputting the results into one of several prediction equations.

One of the most popular equations was developed by the U.S. Navy who, needed a

quick, inexpensive, and reasonably accurate method of assessing the body composition of their personnel.

The Navy developed individual equations for men and women, which take into account gender differences in body fat distribution.

The major advantages of the tape measurement method are that it is simple to perform and only requires a tape measure.

Final words

No matter what type of body fat measurement option you use, we recommend you test as soon as possible after setting a health or fitness goal and continue to monitor regularly. Testing regularly helps you monitor your progress and make sure your program is working for you.



My name is Steven Goldstein

With over 10 years of experience in the fitness industry, I have worked with clients of all ages and fitness levels. From professional athletes to individuals aiming to lose weight, I have helped countless people achieve their goals and improve their overall health through customized training and nutrition plans.

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Consistency leaves clues

Hundreds of clients of all ages, backgrounds, and abilities have put their health in our hands over the years and achieved truly remarkable results. 

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