Body Fat: How To Check It & How To Lose It

Updated: 4 days ago

A spare tyre, the flabby bits, a muffin top, junk in the trunk. Whatever you call it excess body fat can be detrimental to your health and increase your risk of disease. Everyone wants to feel happy and beautiful in their skin but it is important to not let being body positive get in the way of being healthy. This is not ‘fat shaming’ or bullying. This is about giving you the facts and advice you need to lower your risk of disease and be as healthy as possible. But what exactly is body fat for? How can you see how much you have? And how can you get rid of excess fat? These are the questions we’ll answer in this post and more.

What Is Body Fat?

The foods and drinks you consume are converted into energy through digestion to drive all the physiological processes going on in your body. If you eat more than you need, your body converts any excess into body fat, which is then stored within your fat cells around your body for later use. Fat is stored in 2 different places, under the skin (a.k.a. subcutaneous fat) and around the organs (a.k.a. visceral fat). Subcutaneous fat is the fat most people worry about because it covers the muscles and prevents them from having that toned, lean, healthy appearance. However, subcutaneous fat is generally quite low risk to your health. On the other hand, visceral fat is the fat you don’t see, it sits around your organs and is much more dangerous to your health. It is important to know the difference between the 2 types as some methods for assessing body fat levels can only measure subcutaneous fat and may not give an accurate indication of how much body fat you have. Regardless of whether the fat is stored under the skin or around the organs, fat is typically stored in fat cells. The number of fat cells you have is usually fixed on reaching adulthood but how much fat is within each cell can fluctuate greatly. When you rapidly lose weight and then binge out afterward (e.g. when you slim down for a holiday then eat in excess all week), you can trigger the growth of new fat cells, which can make dieting harder in the future. In obese populations, fat can completely fill the cells and fat deposits can start to occur outside of fat cells in random locations around the body. This is why some very large people may have more fat on their belly, or on their thighs, or on their arms, or just about anywhere. I have even seen excess fat deposits in a person’s forehead!

When you lose body fat you keep the same number of fat cells but they will shrink down in size. When fat cells shrink they increase the hormone leptin (a.k.a. the hunger hormone), causing you to feel more hungry and more tempted by food cravings. The ability to store energy for later use is an evolutionary advantage to help survive droughts and famine. However, in the western world, droughts and famine are not a concern and our access to food is 24/7. Nature though hasn’t had time to catch up with this and the backup system for storing fat has not changed. Your capacity to store fat is unlimited and why people can grow to insane sizes. That’s why the world’s heaviest person was able to get to a staggering 635 kg (1,400 lbs)! Now that you know what body fat is for and why you can store so much of it, it’s time to look at ways you can measure your body fat percentage so you can stay in the best of health and/or enhance your performance.

How Do You Measure Body Fat?

There are a number of methods for measuring body fat including tape measure girths, bioelectrical impedance (used in labs, medical centres, gym, and home scales), skinfold calipers (used mostly by personal trainers and sport scientists), hydrostatic weighing or air displacement techniques (used by sports teams and scientists), and DEXA or MRI (favoured by bodybuilders and the gold standard in body composition measurements).

Height to Weight Ratios (i.e. BMI)

Estimating a healthy weight from BMI calculations can be a good guide for most people who are not very active with larger than average amounts of muscle mass. However, trying to calculate an accurate estimate of body fat from a height to weight ratio is not possible.

Chart courtesy of


Measuring the girth of key areas of the body can be an accessible method for estimating your body fat levels that requires no expertise and no specialist equipment. These girth measurements are then used to calculate your estimated body fat percentage or track weight loss/muscle gain progress. However, body fat calculations using these types of measurements can be easily skewed in those who are engaged in high amounts of cardiovascular exercise or have much higher levels of muscle mass. Measurements include:

Photo courtesy of McArdle, Katch, and Katch, Exercise Physiology, 7th Edition

While I would not recommend using this method for tracking changes in body fat it is better than nothing. Therefore, if you wish to calculate your body fat percentage using this method, just google a body fat girth calculator for an easy user-friendly option.

Skin Folds

Skinfold fat measurements work by grabbing a pinch of fat at key sites on the body with a thickness measurement tool called a skinfold caliper. These thickness measurements are then plugged into an equation to estimate your body fat percentage. This technique is often favoured by personal trainers and sport scientists but does require a high level of skill to perform well. In fact, if done correctly it takes quite a while because each skin fold needs to be taken at least 3 times until a median result is produced, each area should be left for 3 - 5 minutes between skin folds to allow the fatty tissue to return to it’s resting state, and a minimum of 3 sites need to be performed (ideally 7 or more) to get an accurate result. In addition to the technical skill required, this technique also tends to under-predict body fat percentage values as it only measures subcutaneous fat levels. This is why sometimes you will hear of some celeb, social media influencer, or athlete claiming to be 1% body fat or similar which isn’t a realistic amount as approx. 3 - 5% body fat is essential fat and most individuals outside of professional bodybuilders will never be this lean (or even want to be).

Bioelectrical Impedance

Bioelectrical impedance analysis (BIA) works by sending a small amount of electricity through your body and recording how long the current takes to travel through you. As your body fat is made up of less than 10% water it does not conduct electricity very well and slows the passing of electricity through your body. Your muscle mass however has over 70% water and conducts electricity very well. Therefore, the faster the electricity gets through, the less body fat you have. This is the same technology you’ll find in many home scales, machines at local pharmacies, or at medical centres and sports facilities. However, the way they work can vary greatly. For example, some send the electrical current through just your legs, others just your arms, and the best kind involves sending multiple currents through the whole body. These are a great option for tracking your progress at home but here are some tips to ensure your results are as accurate as possible:

  • Complete the measurement first thing in the morning before eating and after emptying your bladder.

  • Complete the measurement at the same time every time and in just your underwear or naked.

  • Try to take the measurement 3+ days per week and calculate an average for tracking week on week.

BODPOD / Hydrostatic Weighing

These techniques involve placing you within a sealed chamber and measuring the amount of either air or water that is displaced by your body. The test takes around 3 - 5 minutes and is much more accurate than the above-described techniques. You are required to wear tight-fitting clothing for the greatest accuracy and may need to hold your breath for a short time. The amount of air or water displaced can then be used to calculate your body fat percentage using complex algorithms. This form of body fat measurement is typically favoured by professional athletes and sports teams and is conducted mostly in university sport science or human performance labs. The test can be quite expensive and hard to find a site to perform the test for individuals and as a result, is not a great option for most people.


Dual-Energy X-ray Absorptometry (DEXA or DXA) is the gold standard in body composition analysis and works by passing a specialist x-ray machine over your body while lying down on a medical couch. The technique can take quite some time and does come with the danger of exposing you to x-ray radiation. Originally designed for, and still used for assessing bone density, this test is often favoured by bodybuilders who want the most accurate results possible for measuring body composition. Prices of DEXA scans have decreased massively in the last 5 years and now a scan can be done for less than £100. However, due to the associated health risks and costs, bioelectrical analysis is still the best and most affordable option for tracking your body fat percentage changes on a regular basis, when following the best practice tips listed above.

How Do You Lose Body Fat?

Anyone who has ever been on a diet can tell you that there are many different ways to lose excess weight but very few work long term. In fact, the majority of weight-loss diets are often successful in the first instance but 6 months later, dieters have regained their lost weight and 2 - 3 years later they are heavier than when they started. To save yourself the heartache of constant yo-yo weight loss, make sure you follow the below core principles of effective and long-term weight loss:

  • You must be in a calorie deficit (i.e. the calories you consume are less than the amount you “burn off”).

  • Don’t lose weight too quickly (aim to lose no more than 0.5 - 1% of your bodyweight weight per week).

  • Engage in resistance training 2+ times/week (getting active is essential for weight loss and maintenance, but resistance training is the best for sparing your lean muscle mass while losing weight).

  • Eat more protein (aim to eat 1.6 - 2.2 grams, per kg of bodyweight, per day of protein. This helps you feel fuller for longer and maintain your lean muscle mass).

For a more detailed breakdown on how to lose weight and track your progress, check out our weight loss blog here or get in touch with one of our coaches here for 1-to-1 coaching that’s bespoke to your goals, preferences, and needs. If you’re more of a “do-it-yourself” kind of person, you may be interested in my book Eat Move Perform: Volume 1 - Nutrition & Supplements where you can find all the tools you need to create your own healthy and nutritious diet plan.

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