Beyond the Scale: You Can Do Better BMI and Body Weight

This article is from the Bodyweight section of our Library.

You’ve read that weightlifting is good for health and losing fat  — that’s true. So, you’ve been going to the gym consistently for months. Your clothes fit better, you notice it in the mirror, you feel stronger, and your friends are even making comments about it. 

But when you step on the scale? The number has barely moved — or worse, it's gone up. Frustrated, you wonder if all your hard work has been for nothing: “I’ve not even lost any weight”. 

Here's the truth: the scale is lying to you. And so is your Body Mass Index (BMI) if your doctor bothers to look at that sort of thing.

These popular metrics, while simple and widely used, fundamentally misunderstand what health and fitness progress actually look like. 

We’ll explain how and why these measurements (often) fail, and what you should look at instead.

The BMI Problem:

A 200-Year-Old Tool That Never Fit

BMI was developed in the 1830s by Belgian statistician Adolphe Quetelet. It was not created to measure how fat or how fit a person is; it was created to study “population” trends across thousands of different people all at the same time.

The formula is deceptively simple: take your body weight in kilograms and divide it by your height in meters squared. A BMI over 30 classifies you as obese, while over 25 means overweight.

While BMI correlates reasonably well with health risks across “populations” (i.e., thousands of people all analysed together), it has critical flaws when used at the individual level.

The fundamental issue? BMI cannot distinguish between fat mass and fat-free mass (which includes muscle, bone, organs, and water). It treats all weight equally, when clearly it's not (from a health perspective).

Consider this: if you gain 5 kilograms of healthy muscle through strength training, this is something nearly every scientist and medical expert would agree is beneficial for your health and metabolism. 

However, despite the applause, your BMI will actually increase, suggesting you've become less healthy.

The Exercise Paradox

This limitation becomes particularly problematic for people who are exercising regularly, especially weightlifting, as it’s particularly efficient at stimulating muscle growth. 

Over the course of a training program, you can typically expect increases in skeletal muscle mass to occur alongside decreases in fat mass — a highly desirable outcome.

And in fact, some positive effects of exercise on obesity are actually caused by increases in skeletal muscle, which is a primary site to store excess carbohydrate and increases resting and non-resting energy expenditure.

Yet because changes in muscle mass and BMI are positively correlated, BMI is inappropriate for assessing progress in people who are exercising.

If you’re thinking this doesn’t make sense, you’re right. Yes, the medical community will advise you to exercise for weight loss, then, at the same time, use a flawed measure to assess your progress. Bizarre.

Let me illustrate with a real-world example:

Imagine an obese patient weighing 100 kg (220 pounds) who is 1.8 meters (5 feet 11 inches). Their body fat is 40% (40 kg of fat and 60 kg of fat-free mass), and they have a BMI of 31 31 kg/m².

Over several months of exercise training, they lose 5 kg (11 lbs) of fat while simultaneously gaining 5 kg (11 lbs) of muscle — an excellent outcome representing significant body recomposition.

What happens to their BMI? Absolutely nothing. It remains at 31 kg/m²; they’re still classified as “obese” even though their body fat percentage has dropped from 40 to 35%, and their health will have improved dramatically.

Now, worse: imagine that they only lost 5 kg of fat, they would have reduced their BMI from 31 to 29 kg/m². They would no longer be defined as obese (just overweight), despite not losing a single extra gram of fat, and their body fat would’ve only dropped from 40 to 37%.

It can technically get even worse. Imagine that person skips the gym and loses 5 kg of muscle. They’ll have been moved out of the obese category by their doctor, but their body fat would have gone up from 40 to 42%.

These “paradoxes” reveal why BMI fails as a measure for monitoring progress for people who are exercising.

Any reduction in fat or body fat percentage can be completely offset by concurrent increases in muscle mass, making BMI changes misleading or even discouraging for people doing exactly what they should be doing.

Beyond Fat and Muscle

The problems with scale weight extend even further. Your body weight fluctuates significantly based on factors that have nothing to do with actual fat gain or loss:

Water and Carbohydrate

Even if you’re drinking the same amount of water every day, the amount of water in your body can vary by several pounds day-to-day based on your sodium intake, hormones, inflammation, menstrual cycle, stress, and medication.

After eating carbohydrate-rich meals, your body stores carbohydrate for energy (“glycogen”) in muscles and the liver. Each gram of glycogen stored in your muscle takes 3–4 grams of water with it.

This is why low-carb diets produce rapid initial “weight loss” after a few days — it's primarily water and glycogen, not fat.

Starting a new exercise program often causes temporary “water retention” in your muscles to repair and adapt. This means you could be burning fat while the scale stays the same or even increases due to water weight — another way the scale misleads you about your actual progress.

Two People, Same BMI, Two Different Health Profiles

BMI also fails to account for where fat is stored, which profoundly affects health risk. Two different people with identical BMIs can have vastly different body compositions and health profiles. 

One person might carry most of their fat subcutaneously (under the skin), while another may have a lot of dangerous visceral fat around internal organs.

Visceral fat is metabolically active and strongly associated with cardiovascular disease, type 2 diabetes, and other health complications. Subcutaneous fat, while not ideal in excess, is relatively benign. BMI treats these two types of fat equally, missing a crucial distinction for health.

The concept of "metabolically healthy obesity” or “fat but fit” illustrates this further. While uncommon, some people are classified as obese by BMI but have normal health markers — maybe because they exercise regularly and have a lot of muscle despite also carrying extra fat.

Given these substantial limitations, what should you track to assess genuine health and fitness progress?

The correct answer depends on your goals, resources, and preferences, but there are several alternatives to consider that are more informative than BMI or scale weight alone.

We’ll start with the simplest, most accessible methods you can use at home first.

Waist Circumference: Simple and Effective

Waist circumference offers a practical alternative that better predicts health risk than BMI. 

A waist measurement over 40 inches (102 cm) for men or 35 inches (88 cm) for women — or more than half your height, regardless of sex — indicates abdominal obesity and increased disease risk.

Why this works better: Waist circumference correlates strongly with abdominal fat and visceral fat. It also remains relatively unaffected by muscle gain from exercise, unlike BMI.

For people participating in exercise programs, where muscle increases occur primarily in the upper body and limbs, hip and waist measurements can provide a viable, accurate alternative to BMI.

How to measure correctly:

• Use a flexible measuring tape, not one you use for measuring the skirting board.

• Measure first thing in the morning before eating

• Find the narrowest part of your torso (usually just above the belly button)

• Keep the tape parallel to the floor

• Breathe normally and measure after a natural exhale

• Don't suck in or compress your abdomen

• Measure at the same location each time

Track this measurement weekly. A cheap measuring tape may be the most valuable progress-tracking tool you can buy. Although it’ll be less accurate, the fit of your trousers or belt will tell the same story.

Progress Photos and Measurements

Never underestimate the power of visual documentation. There’s a reason why marketers use the before and after photos to sell their products.

Progress photos, taken under consistent conditions, can provide good visual evidence of body composition changes that scales and BMI completely miss.

How to take effective progress photos:

• Wear the same minimal clothing each time (swimsuit or underwear)

• Use the same lighting and location

• Take front, side, and back views

• Shoot at the same time of day (morning is ideal)

• Use the same camera distance and angle

• Don't judge day-to-day — compare photos months apart

To confirm what you think you’re seeing in the photos, combine them with body measures (other than your waist) using your measuring tape.

Measure your chest, upper arms, thighs, hips, or calves. These measurements can hint at where you're losing fat or building muscle, providing a more complete picture than a single number can.

The Bigger Picture: Other Measures

Health isn't just about how you look or what you weigh — it's about what your body can do. Tracking some simple “performance” metric can provide some good supporting information and additional motivation. Examples include:

• Strength gains: How much weight can you lift? Are you progressing on key exercises?

• Endurance: How far or long can you run, walk, cycle, or swim?

• Function: Can you play with your kids longer? Carry more groceries? Get off the floor easier?

• Energy levels: How do you feel throughout the day?

• Sleep quality: Are you sleeping better? Are you sleeping longer?

• Resting heart rate: Lower is generally better? Take a 15-second measure.

These functional improvements often come before the more visible physical changes and can tell you that your exercise program is working, even when the scale doesn’t budge.

Metabolic Health Markers: What's Happening Inside

Here's a crucial realisation: fat loss isn't always medically essential if your metabolic health markers are good. 

Direct health measures provide the most important information of all — what's actually happening in your body. Blood pressure, blood sugar, blood lipids, and inflammation can all be used to determine if you may need to lose fat, and can be used to track progress.

Losing muscle, glycogen, and water may shift the scale weight, but it is unlikely to improve any of these health markers. 

It is also possible to have a high BMI or body weight and be perfectly healthy (termed “metabolically benign obesity”) — more reasons why the scale doesn't tell the complete story.

Body Fat: The Technical Gold Standard

Here's something that should be obvious but often isn't: obesity is defined by having “excessive body fat”, yet we typically don't measure body fat to diagnose or track it. Bizarre.

This is like diagnosing anaemia without checking blood iron levels.

Body fat percentage is the most common way of expressing the amount of body fat you have. It really tells you what “proportion” of your total weight comes from fat versus fat-free “lean tissue” (like muscle, bone, organs, water).

This is the metric that truly reflects whether you're improving body composition, regardless of what happens to total body weight. It accounts for changes in muscle AND fat. Healthy values range from 10-20% for men and 20-30% for women.

How to Measure Body Fat:

Bioelectrical Impedance Analysis (BIA): Found in smart scales and handheld devices, BIA sends a weak electrical current through your body. Fat and muscle conduct electricity differently, allowing the device to estimate your body composition.

Pros: Inexpensive, convenient, can track trends at home.

Cons: Accuracy varies significantly based on hydration status, recent meals, exercise, and device quality. Absolute numbers may be off by several percentage points.

Best use: Tracking changes in the numbers rather than what the numbers actually are. Measure under consistent conditions (same time of day, hydration level).

Skinfold Callipers: A trained practitioner pinches your skin at specific sites and measures the thickness with callipers, then uses some equations to estimate your body fat.

Pros: Relatively inexpensive, portable.

Cons: Accuracy depends heavily on the skill of the person who’s doing it. It is difficult to do it on yourself consistently, and less accurate for very thin or very fat people.

Best use: When performed by an experienced practitioner for periodic assessments

DEXA scan (Dual-Energy X-ray Absorptiometry): This is the clinical gold standard. Originally developed to measure bone density, DEXA scans use low-dose X-rays to precisely measure bone mass, fat mass, and lean mass throughout your entire body.

Pros: Highly accurate, shows exactly where fat is located (or has been lost/gained), measures visceral fat, reveals muscle distribution, provides bone density data

Cons: More expensive ($50-150 per scan), requires travelling to a facility, and involves some radiation exposure.

Best use: Baseline assessment and periodic check-ins (every 3–12 months) to track comprehensive body composition changes.

Hydrostatic (Underwater) Weighing: Considered very accurate, this method weighs you underwater to determine body density and calculate your body fat.

Pros: Highly accurate when done properly.

Cons: Uncomfortable for many people, requires specialised equipment and facilities, and is inconvenient.

Best use: Research settings or baseline assessments if DEXA unavailable

Putting it All Together

Although some measures are better than others, no single metric can be used to get the whole picture of what is happening to your body. So why not take are few of them at the same time? 

Waist circumference and body weight can be measured weekly. Progress photos and body size measurements can be done monthly. 

Then, if you need them, can afford them, and have access to them, maybe you can include more technical measures, like professional body composition assessment or blood work, which can be taken every quarter, annually or biannually.

Bottom Line

While BMI is a cheap and practical tool for screening or epidemiology, it's not appropriate for monitoring individual progress or health, specifically for anyone who is, or about to start, exercising regularly.

A simple alternative, waist circumference, is a better measure. And can be used alongside body weight to indicate that the scale changes are actually beneficial for health.

Of course, more technical, professionally administered measures are available (to some people). But simpler, cheaper progress photos, how your clothes fit, and your performance metrics can also be used to track or confirm progress.

So next time you’re on the scale, remember: it’s just one data point that doesn’t always reflect your true health status by itself. There are other measures available that more accurately reflect your health.

Progress is progress, whether the scale agrees (or not).

Disclaimer: No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.