The Hidden Risk: Normal Weight Obesity
When most people think of obesity, they imagine something obvious — someone who looks clearly overweight. But there’s a form of obesity that can hide in plain sight, even in people whose weight looks “normal” on the outside.
It’s called normal weight obesity — sometimes nicknamed TOFI, short for Thin Outside, Fat Inside.
What Is Normal Weight Obesity?
This happens when someone has a normal body mass index (BMI) but a high amount of visceral fat — the unhealthy fat stored deep in the belly, wrapped around the organs.
That’s different from subcutaneous fat, which sits under the skin. While subcutaneous fat can be visible, visceral fat is the kind that raises your risk for serious health problems.
You can also be classified as obese by body fat percentage:
Men: More than 25% body fat
Women: More than 32% body fat
That means you can look “normal weight” by BMI but still be in the obesity range when it comes to actual fat content in your body.
Why It Happens
A big reason is low muscle mass. Muscle is protective for your health, and some people have naturally less of it — whether from genetics, aging, or inactivity.
Certain populations — especially East Asian and South Asian — tend to have less muscle mass and more visceral fat at lower body weights. This condition is more common in these groups but can happen to anyone, regardless of background.
Why BMI Isn’t the Whole Story
BMI is a quick screening tool, but it doesn’t measure fat vs. muscle. Similarly, high BMI also may not give the full picture but more on that another time.
For most people:
Overweight = BMI 25–29.9
Obese = BMI 30 or higher
For many Asian populations:
Overweight = BMI 23 or higher
Obese = BMI 25 or higher
That means someone with a “healthy” BMI in the U.S. might already be at higher risk in other parts of the world.
Why It Matters
People with normal weight obesity have a higher risk of:
Type 2 diabetes and prediabetes
High blood pressure
Heart disease
Fatty liver disease
The danger is that both patients and doctors may overlook the problem because it doesn’t fit the usual image of obesity.
How to Check for It
You can’t tell just by looking. Better ways to measure include:
Body composition scan — often done with a special scale (bioelectrical impedance) or a DEXA scan.
Waist circumference — over 40 inches in men or 35 inches in women suggests higher risk.
Waist-to-height ratio (WHtR) — a newer, simple test. Your waist should be less than half your height.
0.50–0.59 = elevated risk
0.60 or higher = high risk
The Bottom Line
Even if the scale says you’re a “normal” weight, your body composition could be telling a different story.
If you’re having issues like high blood sugar, high blood pressure, or abnormal cholesterol despite not appearing overweight, talk to your doctor about whether normal weight obesity could be the reason.
References:
WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet. 2004;363(9403):157–163. doi:10.1016/S0140-6736(03)15268-3
Romero-Corral A, Somers VK, Sierra-Johnson J, et al. Normal weight obesity: a risk factor for cardiometabolic dysregulation and cardiovascular mortality. European Heart Journal. 2010;31(6):737–746. doi:10.1093/eurheartj/ehp487
Ashwell M, Gunn P, Gibson S. Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: systematic review and meta-analysis. Obesity Reviews. 2012;13(3):275–286. doi:10.1111/j.1467-789X.2011.00952.x