Many people feel reassured when their BMI falls in the normal range. The scale shows a healthy number, the ratio of weight to height looks right — and at a time when obesity rates are high, a normal BMI can feel like a significant achievement.
But a growing body of research suggests that BMI alone can miss a substantial metabolic threat. It is entirely possible to carry a normal BMI while harbouring a risk factor that sharply raises the odds of a heart attack or stroke — without any clinical flag being raised, and without realising it.
The gap exists because BMI does not account for where fat is stored. If BMI is not paired with an additional, crucial metric, cardiovascular risk can remain elevated and invisible to standard screening. That metric can be checked at home in under a minute with nothing more than a flexible tape measure.
This article unpacks what slips through the cracks when BMI is the only measure used, what a large international study found when it examined the combination of normal BMI and hidden fat accumulation, and how to take the measurement correctly at home.
Table of Contents
- BMI and Health Risks
- Visceral Fat and Health Risks
- The New Study
- How to Measure Your Risk
- References
BMI and Health Risks
There is a very good reason clinicians pay attention to BMI. It has been linked with a host of negative health outcomes, ranging from type 2 diabetes to heart attacks and strokes.
A meta-analysis examining the relationship between overweight/obesity and the risk of developing type 2 diabetes found that, compared with those of normal weight, the risk was a sobering 7 times as high for individuals whose BMIs fell in the obese range [1].
Deaths linked to heart disease are 2 to 3 times more likely with a BMI of 35 or above [2].
The mechanism is multifactorial, but one of the most important pathways is the way excess body fat drives inflammation. Stored fat is not simply a passive energy reserve — adipose tissue actively pumps out inflammatory compounds, raising levels of inflammatory markers in the blood of people who are overweight.
Research has established that the adipose tissue of lean individuals predominantly secretes anti-inflammatory markers, while in obese individuals, more pro-inflammatory markers are secreted. Overweight and obese individuals show altered serum levels of inflammatory cytokines — including tumor necrosis factor-alpha (TNF-α), C-reactive protein (CRP), interleukins (IL-6, IL-18), resistin, and visfatin.
The evidence is increasingly pointing to chronic inflammation as a key driver of conditions like heart disease [3]. But as research has revealed, not all fat produces the same inflammatory signal — and that distinction is where BMI falls short.
Visceral Fat and Health Risks
A surprising finding has come into focus in recent years: not all fat is created equal. This is precisely why an additional metric beyond BMI is needed.
The fat most easily noticed is the kind stored just under the skin — subcutaneous fat. But a distinct type accumulates deeper inside the body, in the spaces surrounding the heart, liver, intestines, and other organs. This is called visceral fat, often referred to colloquially as belly fat [4].
Subcutaneous fat does not appear to link to type 2 diabetes in the same way. Visceral fat, by contrast, is strongly linked to insulin resistance. A standard deviation increase in visceral adipose tissue mass increases the odds of insulin resistance by 80% [5].
Similarly, the chronic inflammation associated with obesity is primarily driven by visceral fat — not subcutaneous fat [6]. This helps explain why two people with identical BMIs can have very different metabolic risk profiles depending on where their body fat is stored.
This is why BMI alone does not tell the whole story. BMI represents the ratio of weight to height squared, expressed in kilograms and metres. A person weighing 70 kg (approximately 155 pounds) and standing 1.75 metres (approximately 5 feet 9 inches) tall would have a BMI of 22.86 — squarely in the normal weight range.
Yet it is entirely possible for that person to carry a normal BMI while also harbouring excess visceral fat. A common example is someone who appears lean across most of the body but carries a pronounced stomach — a pattern that, particularly in men, is driven by excess visceral fat rather than subcutaneous fat [7].
BMI simply cannot distinguish between these two fat types, because it measures total mass relative to height — not fat distribution. That blind spot is what the additional metric addresses.
The New Study
What are the actual health risks when BMI is normal but significant visceral fat is present? A major study published in JAMA Network Open set out to answer exactly that question [8].
The researchers drew on a comprehensive dataset from the World Health Organization, spanning surveys conducted across 91 countries between 2000 and 2020 — a total of approximately 470,000 participants [8].
The analysis focused specifically on adults with normal weight according to BMI (18.5–24.9) but with a high waist circumference: defined as ≥80 cm for women and ≥94 cm for men [8].
Waist circumference at these thresholds serves as a validated and convenient proxy for visceral fat accumulation. It is also the metric most frequently overlooked in routine clinical practice. Most global guidelines continue to rely on BMI as the primary tool for obesity-related risk assessment — which means the normal-BMI-but-high-waist-circumference group is systematically under-screened.
Within this subgroup, the researchers examined associations with four cardiometabolic markers: blood pressure, type 2 diabetes, total cholesterol, and triglycerides [8]. The findings were clinically significant:
- A 29% higher likelihood of high blood pressure
- An 81% higher likelihood of type 2 diabetes
- A 40% greater risk of high total cholesterol
- A 56% higher risk of elevated triglycerides [8]
The data also revealed that this combination — normal BMI alongside high visceral fat — is far from uncommon. Approximately 1 in 5 adults globally fit this description [8].
The researchers underline that this creates a significant problem. Because waist circumference is so often absent from routine check-ups, and because most screening protocols rely on BMI alone, a large proportion of the population may be carrying elevated cardiometabolic risk without any clinical signal pointing to it [8].
That makes self-measurement not just a useful option, but a practical and important step anyone can take independently — particularly those with a normal BMI who have never had their waist circumference assessed.
How to Measure Your Risk
The measurement is straightforward and can be completed at home — but accuracy depends on measuring in the correct location. The most common mistake is measuring around the widest part of the abdomen or the navel, which can produce inaccurate readings.
Here is the correct procedure:
While standing, locate the very top of the hip bone at the side of the body. This bony landmark — called the iliac crest — is the reference point for the measurement. Using a flexible tape measure, wrap it around the body at this level. Looking in a mirror helps ensure the tape remains level all the way around. Take the reading at the end of a normal, relaxed breath — not after inhaling or pulling in the stomach.
Research has confirmed that self-measured waist circumference at home is approximately as accurate as a measurement taken by a trained technician in a clinical setting [9], making this a reliable screening tool that does not require a clinic visit.
To interpret the result, apply the thresholds established in the WHO-dataset study, relevant for adults with a BMI in the normal range (18.5–24.9):
- Women: ≥80 cm (31 inches)
- Men: ≥94 cm (37 inches) [8]
A waist circumference at or above these thresholds — in a person whose BMI is otherwise normal — places them in the group the study found to carry significantly elevated cardiometabolic risk, including higher odds of high blood pressure, type 2 diabetes, raised cholesterol, and elevated triglycerides [8].
For anyone whose numbers exceed these thresholds, the practical next step is a conversation with a healthcare provider about a more complete metabolic assessment. A fasting blood glucose or HbA1c, a lipid panel (including LDL, HDL, and triglycerides), and a blood pressure check together provide a far fuller picture of cardiovascular health than BMI alone — and can identify areas for lifestyle intervention well before symptoms appear.
References
- https://pubmed.ncbi.nlm.nih.gov/20493574/
- https://www.mdpi.com/2073-4409/10/3/629
- https://www.jacc.org/doi/10.1016/j.jacc.2025.08.047
- https://my.clevelandclinic.org/health/diseases/24147-visceral-fat
- https://pmc.ncbi.nlm.nih.gov/articles/PMC4038351/
- https://www.ahajournals.org/doi/10.1161/CIRCRESAHA.125.327146
- https://pmc.ncbi.nlm.nih.gov/articles/PMC6906176/
- https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2840296
- https://www.nature.com/articles/s41574-019-0310-7
