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How To Measure Body Fat

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When it comes to losing weight and tracking progress, most people use the scale. However, this may not be the best way to track your progress, especially as you get close to your target weight. Body fat and body measurements offer a far better way to track your progress. So why is it important to track body fat?

Losing Weight is Not the Same as Losing Fat

The problem with scales is that they don't tell us anything about our body composition and body fat level. Focusing purely on weight can be misleading: you don't know whether you are losing fat, muscles or even water.

In fact, water loss is a natural result of carbohydrate withdrawal and is the biggest contributor to weight loss during the initial phase of the ketogenic diet. That's why you may experience an initial rapid weight loss. Give it a couple of weeks before you start measuring your body fat and keep measuring every few weeks.

Ketogenic diets have a muscle-sparing effect and will help you preserve and build lean mass. However, muscle loss may occur if you don't eat enough protein and/or you don't eat enough fat and therefore calories. Make sure you are eating enough to avoid any unwanted muscle loss. You should never feel hungry when you follow a ketogenic diet.

How To Measure Body Fat

Body Fat Helps Calculate Protein Intake Accurately

Knowing your body fat is essential for calculating your macros accurately: your protein intake is determined by your lean mass - not total weight. That's why it's important to know your body fat so your lean mass can be calculated.

Once you know your body fat, you can use our Keto Calculator to find out your macros.

You May Gain Weight with Exercise

If you exercise, your overall weight may go up. Don't panic and remember, compared to body fat, muscles are heavier and more compact. The more muscle your gain, the more likely you will experience a weight gain. If you think your weight has been stalling as you get close to you target weight, focus on your body fat, not your weight.

Below is an example of men and women who have similar body fat content but different body composition and different weight. Even though their body fat is similar, a muscular individual weighs more than a thin individual. In fact, the total body weight and Body Mass Index (BMI) of a muscular individual can be the same as that of an overweight sedentary person. That's why I rarely weigh myself - I only track my measurements and body fat.

Not seeing any progress? Ditch the scales and track your body fat instead!

How to Measure Body Fat

Skinfold Calipers and Body Fat Calculator

My preferred way to measure body fat is with skinfold calipers. They measure the thickness of the skin and therefore subcutaneous fat at specific areas of your body. Depending on the methodology you use, you can either do it yourself or ask a friend to help you. Some formulas require 9 areas of measurement, while others require only 3 areas. The numbers are then compared to a large statistical number of skinfold measurements and used to calculate total body fat.

How To Measure Body Fat

Skinfold calipers are inexpensive, easy to use and can be fairly accurate. The accuracy is dependent on a person's unique body fat distribution and several other factors: age, areas that are measured, racial differences, or visceral fat that can't be measured using this method (only subcutaneous fat is measured). Although calipers may not give you an accurate reading of total body fat percentage, they are a reliable measure of body composition change over a period of time. Always measure at the same location and using a fixed pressure to get most accurate results.

To help you calculate your body fat percentage using skinfold calipers, we developed a free online Body Fat Calculator. It only requires four measurements to estimate your body fat level. Once you know your body fat level, you can use our Keto Calculator to calculate your macros accurately.

Visual Estimates

You can get an approximate number by using comparison photos. This is not an accurate way of measuring body fat but will give you a rough idea of your body fat level.

Visual Estimates for Women

How To Measure Body Fat

Image courtesy of

Visual Estimates for Men

How To Measure Body Fat

Image courtesy of

Bioelectrical Impedance Analysis (BIA)

In simple terms, the principle behind the BIA method is using two conductors attached to your body, sending a small current through and measuring the resistance between the two conductors. The resistance between fat, muscle and skeletal tissue varies and that's how BIA measures body fat.

Although BIA has shown some promising results, the devices using this technology (scales and handheld analysers) produce inaccurate results because they only measure a small part of your body and approximate the rest of it. The way BIA scales work is that they send a current up one leg and down the other. If you are pear-shaped, your measured body fat can be a lot higher than your actual body fat. Similar to BIA scales, handheld BIA analysers only measure part of your body (the upper part). DMS-BIA is a new technology that could potentially respond to these issues.

DXA (Dual-energy X-ray absorptiometry) and Other Methods

DXA also known as  DEXA scans are primarily used for measuring bone mineral density. Additionally, they can be used to measure total body composition and body fat content. DXA is an accurate way to measure body fat but can be expensive ($60 to $100 per scan) as compared to getting skinfold calipers ($7).

Apart from DXA which is the gold standard of body fat measuring, there is  Hydrostatic Weighing and  Near-Infrared Interactance. Both offer accurate results but are pricey and not easily available.

Bottom line: If you decide to measure and track body fat and can't afford DXA, use skinfold calipers. Do not use BIA scales and handheld devices that offer body fat measuring. Calipers are inexpensive, easy to use and can be fairly accurate.

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Martina Slajerova
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Martina Slajerova

I changed the way I ate in 2011, when I was diagnosed with Hashimoto’s, an autoimmune disease that affects the thyroid. I had no energy, and I found it more and more difficult to maintain a healthy weight.

That’s when I decided to quit sugar, grains, and processed foods, and to start following a whole-foods-based ketogenic approach to food.

About the Reviewer

This article has been reviewed by Franziska Spritzler, RD, CDE who is a qualified expert. At KetoDiet we work with a team of health professionals to ensure accurate and up-to-date information. You can find out more on the About us page.

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