When you’re starting your weight loss journey, there are a lot of new terms that you may come across as you try to familiarize yourself with all the ways that practitioners assess health related to weight.
Terms like body mass index (BMI) or body fat percentage (BF%) get thrown around a lot online, but what should they really mean to you? This page will explore the similarities and differences between BMI vs body fat percentage to help you better understand your health, as well as how these factors relate to your body size.
SIDE NOTE: We should note here that many different studies have shown different accuracy in numbers relating to BMI and BF% calculation. Additionally, each person’s body reacts differently to weight loss, which can impact the accuracy of how these statistics apply to varying health outcomes.
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What is BMI?
Body mass index, or BMI, is a simple, easy-to-calculate formula that allows practitioners to quickly estimate your level of body fat.
However, it’s important to remember that BMI is not the same as body fat percentage calculations. BMI is simply faster and easier to calculate, which is why it’s used by many public health professionals to track things like increased risks for weight-related conditions in certain regions, as well as planning for potential public health needs.
How BMI is Calculated
The BMI formula is your weight (in kilograms) divided by your height (in meters squared). For the imperial measurement, you divide your weight in pounds (lbs) by your height in inches (in) squared, then multiply the result by 703.
These results will be calculated against 4 tiers of measurement:
- Underweight: Any BMI under 18.5
- Normal: BMIs between 18.5 – 26.9
- Overweight: BMIs between 27 – 30
- Obese: Any BMI over 30
SIDE NOTE: It’s important to note that a BMI of 30 is not the threshold for every ethnicity. For example, in Asian populations, a BMI between 25 and 27.5 can be considered obese, depending on the region.
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Limitations of BMI
It’s important to note that BMI doesn’t take into account certain other factors that body fat percentage calculations will, such as age or gender.
BMI calculations also don’t take into account muscle vs fat weight, which is why many athletes may have high BMIs, even though they have low body fat percentages. Or things like bone density, fat distribution, or individual health differences, which can lead to misleading results.
While the old saying ‘muscle weighs more than fat’ isn’t true, BMI measurements don’t differentiate between muscle and fat (i.e., a pound of muscle is treated the same as a pound of fat). This means it won’t accurately reflect the health of certain types of people, like patients under 18, the elderly, and those who are pregnant and/or lactating.
Because your height won’t change as you lose weight, a slim person with a lot of lean muscle could actually weigh the same as someone who looks physically larger but doesn’t have the same level of muscle density. That’s one reason why the number on the scale doesn’t tell the whole story of one’s health.
Despite BMI being a quick-to-use and convenient screening tool based on height and weight, because of its limitations, your practitioner typically considers other elements into account when assessing your health.
What is Body Fat Percentage?
Body fat percentage is an estimate of how much of your total weight is composed of fat versus fat-free mass (which includes your muscles, bones, and water).
While BMI only looks at your total weight relative to your height, body fat tests attempt to ‘see’ inside that weight to provide a more detailed map of your body composition.
Water is a significant variable in the accuracy of tests that measure body fat percentage. If, for example, someone is dehydrated or has just eaten a very salty meal, the body fat scale may give a different answer than normal, because it confuses water fluctuations with tissue changes in your body.
How Body Fat Percentage is Measured
There are a number of different ways to measure body fat percentage, and while some can be expensive or difficult to access, there are a few options here. Although not every test will offer equally accurate or detailed results:
Easily Accessible, Affordable & Slightly Less Accurate Methods
Body Circumference Tests: This is calculated by measuring the circumference of your waist, hips, and neck, along with your weight and your height. This is the least accurate of this level of testing, although it can still provide insights that can be helpful when used in addition to other things, like a regular BMI calculation.
Skin Calipers: This is a special device used by practitioners to measure skin folds at certain areas of your body, and can actually be quite accurate if done at multiple locations on the body by a highly skilled professional with good quality calipers.
Bioelectrical Impedance Analysis (BIA): In this method, a small electrical current is sent through your body to measure the resistance, which is then used to calculate an estimate of your body fat percentage. It is the most accessible and quickest method, though its results can fluctuate based on your hydration, recent meals, or exercise. Additionally, accuracy also varies depending on the quality of the equipment used, with professional vs home equipment varying significantly in accuracy.
Less Accessible, More Expensive & More Accurate
Hydrostatic Weighing: Determines your body density by comparing your weight on land to your weight while submerged in a water tank. While highly accurate, it requires the patient to exhale all air from their lungs while underwater, which can be difficult or uncomfortable for some. It can also be difficult to locate local facilities to access this type of measurement.
Air-Displacement Plethysmography (Bod Pod): To perform this measurement, you must sit in a sealed chamber so that it can measure the density of your body by the volume of air you displace. Also very accurate, but again, this can be difficult to access, depending on the type of testing facilities that are available in your area.
Dual-Energy X-Ray Absorbiometry (DEXA): A DEXA scan is widely considered the most precise single test available. By using two low-level X-ray beams, it provides a highly detailed map of bone mineral density, lean muscle mass, and fat distribution (including dangerous visceral fat) in specific areas of the body. Still, it may be difficult to locate nearby, as it is also done at a special testing facility.
While these professional tests offer improved accuracy, they are often used as ‘milestone’ measurements (e.g., once or twice a year) rather than for weekly tracking, due to their cost and the specialized equipment required.
Healthy Body Fat Percentage Ranges for Men & Women
While there is some overlap, it’s very important to remember that the healthy body fat percentage for men and women isn’t the same. And there is no one consensus on the exact range that men or women have for a healthy body fat percentage, particularly because some studies show that these numbers can change over time. Just as excess body fat carries risks, body fat levels that are too low can also pose significant health concerns.
While ideal ranges can vary based on age and activity level, general clinical estimates for healthy body fat percentages include:
- Men typically range between 11% – 22% body fat
- Women typically range between 20% – 32% body fat
Women naturally maintain a higher percentage of essential body fat, which is the fat required for hormonal regulation and reproductive health. So it’s natural that the healthy body fat percentage for men or women would vary.
These are only generalized figures as well, and it’s extremely important to remember that factors such as genetics, ethnicity, and individual biological predispositions mean that a ‘healthy’ composition can look different for everyone.
Limitations of Body Fat Percentage Measurements
The truth of the matter is that there will always be a margin of error, no matter which type of body fat percentage testing you’ve done.
Science and testing technology are always improving, but even with innovations, testing is something that’s designed to be done generally, so that it can provide accurate results for any type of person who takes the test.
Put simply, one of the biggest limitations of body fat percentage measurements is being able to take every person’s individual health, genetics, age, gender, etc., into account – all simultaneously. Additionally, hydration status and recent meals can influence many of the tests.
This can lead to slightly different results for different people and even variations in the same person on different days, which is why it’s so important to have a practitioner on your team to help you interpret and create actionable insights that also take into account your lifestyle and health goals. Need a practitioner?
BMI vs. Body Fat Percentage: Key Differences
The key differences between BMI and body fat percentage are the number of different factors that are taken into account to provide accuracy in the result.
BMI only uses height and weight, which is great for providing a quick, general answer, but it doesn’t give you a full picture, especially if you have a lot of body mass that isn’t fat.
Body fat percentage testing isn’t perfect, but it often provides a level of accuracy that’s simply not possible with BMI-exclusive testing, since it includes other factors when making estimates.
Which is More Accurate?
Between BMI vs body fat percentage, body fat percentage is the more accurate of the two types of testing. In some cases, significantly more so.
That’s because BMI only takes into account height and weight, while (depending on the type of BF% testing you’re having done) body fat percentage testing takes multiple other elements into account as well.
So, if you’re looking for a more accurate calculation of your body composition, body fat percentage is the way to go.
Who Should Use BMI vs. Body Fat Percentage?
Why not both? Start by using Felix’s BMI calculator to figure out your BMI. It’s free, and it will only take a minute to provide you with the answers you need.
Whether you’re a man or a woman, wanting to improve your health is something to strive for, even if it can sometimes feel like an uphill battle.
Need some support during your weight loss journey? Check out Felix’s Weight Loss Program to see how we can help with your weight management with personalized insights and custom-tailored treatment plans.
How to Improve Your Body Composition
Working towards your best weight, the weight that represents what is most healthy and sustainable for your body, encourages long-term health and realistic lifestyle changes that support overall wellbeing, and is an important goal. Your best weight does not always correspond to a specific number on a scale, a specific BMI, or an exact percentage of body fat.
Healthy nutrition, regular physical activity that includes resistance activities, and getting enough sleep each night are all things that are important for your health journey. We take into account a wide array of information, such as your gender, ethnicity, and body composition (i.e., waist circumference).
This way, we can provide guidance for those who are also at high risk for cardio-metabolic complications that are also associated with increased body mass, so your healthcare practitioner can create a personalized treatment plan for you.
If you’d like to talk to a practitioner about what types of additional weight management tools may be appropriate for you, then consider completing a short online assessment today.
With Felix in your corner, you can take control of your health, all while getting back to living life on your terms – the way it should be.
