170cm and 68kg Feels Normal — Until BMI Says Overweight

I walked out of my annual checkup feeling pretty good about myself. 170cm, 68kg — that's a perfectly average build, right? Then the doctor pointed at a number on my results sheet: BMI 23.5. Overweight. I laughed, assuming it was a mistake. It wasn't. By Korean health standards, I had officially crossed the line into overweight territory. The weird part? By WHO international standards, I was still normal.

That moment sent me down a rabbit hole. What exactly is BMI? Why do Korea and the WHO disagree on what's overweight? And should I actually be worried about a number that can't tell the difference between muscle and fat? Turns out, the answers are simpler than I expected — and genuinely useful once you understand them.

What Is BMI, Exactly?

BMI stands for Body Mass Index. It's a single number that tells you whether your weight is proportionate to your height. A Belgian mathematician named Adolphe Quetelet came up with the formula back in the 1830s, and nearly 200 years later, hospitals worldwide still use it. The concept is dead simple: take your weight in kilograms and divide it by your height in meters, squared.

That's it. No blood tests, no fancy equipment, no doctor's appointment needed. Just two numbers you already know. The result gives you a rough estimate of where you fall on the spectrum from underweight to obese. It's not perfect — and we'll get into why — but it's a solid starting point.

The BMI Formula

The math is straightforward. You convert your height to meters, square it, then divide your weight by that number. If you're 170cm, that's 1.70 meters. Square that and you get 2.89. Divide your weight by 2.89 and you have your BMI. Let's walk through a real example.

See the problem already? The same BMI of 23.5 gets two completely different labels depending on which standard you use. This isn't a glitch — there's a real medical reason for it, which we'll cover next.

Korean BMI Categories vs WHO Standards

Here's where it gets interesting. Korea uses stricter cutoffs than the WHO. If you've ever Googled your BMI and felt relieved to see "normal," you might have been looking at WHO standards without realizing Korean health guidelines draw the line earlier.

The key difference: WHO says overweight starts at 25, but Korea says it starts at 23. That two-point gap isn't arbitrary. Research shows that East Asian populations tend to carry more visceral fat — the dangerous kind that wraps around internal organs — at lower BMI levels compared to Western populations. The WHO Asia-Pacific regional office actually recommended these lower thresholds, and Korea, Japan, China, and Taiwan all adopted similar standards.

Why BMI Gets It Wrong Sometimes

BMI has a fundamental flaw: it can't tell the difference between muscle and fat. A 180cm rugby player weighing 95kg gets the same BMI score as someone of the same height and weight who never exercises. Their health profiles could be worlds apart, but BMI treats them identically.

Age is another blind spot. As you get older, you naturally lose muscle mass and gain fat. A 65-year-old with a BMI of 22 might look healthy on paper, but their body composition could have shifted dramatically — less muscle, more fat — while the number stayed the same.

Gender matters too. Women naturally carry more body fat than men. A BMI of 23 means different things for male and female bodies, but the formula doesn't account for this at all. And fat distribution — arguably the most important factor for health risk — is completely invisible to BMI. Belly fat is far more dangerous than fat stored in the hips or thighs, but BMI can't tell the difference.

Better Metrics to Check Alongside BMI

If BMI is just the starting point, what's the full picture? Three additional measurements give you a much more accurate read on your health.

First: waist circumference. This is the simplest way to estimate visceral fat. Measure at belly-button height with a tape measure. For men, anything over 90cm is a red flag. For women, over 85cm. These are the Korean guidelines. Even if your BMI is normal, a large waist circumference can signal hidden health risks.

Second: body fat percentage. If you've ever used an InBody machine at a gym or clinic, that's what it measures. Healthy ranges are roughly 10-20% for men and 18-28% for women. It's not perfectly accurate, but it tells you far more than BMI about what's actually going on inside your body.

Third: waist-to-height ratio. This one is beautifully simple — your waist should be less than half your height. If you're 170cm, keep your waist under 85cm. This metric works across ages and genders, which makes it especially practical.

Using BMI the Smart Way

So should you ignore BMI entirely? No. It's a quick, free, no-equipment screening tool that gives you a rough sense of where you stand. The key is knowing what it can and can't tell you.

Use BMI as a starting point, not an endpoint. If your number falls outside the normal range, that's a signal to dig deeper — get your body fat measured, check your waist circumference, talk to a doctor. If your BMI is normal but you have a large waist or you're sedentary, don't assume you're in the clear.

And if you're Korean or of East Asian descent, use the Korean/Asian-Pacific standards, not the WHO ones. That two-point difference between BMI 23 and 25 isn't academic — it reflects real differences in how your body stores fat and responds to metabolic risk.